Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Exploring the resistance against root parasitic plants in Arabidopsis and tomato
    Cheng, Xi - \ 2017
    Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): C.P. Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463437004 - 305
    plants - parasitic plants - arabidopsis thaliana - solanum lycopersicum - host parasite relationships - plant growth regulators - resistance - planten - parasitaire planten - arabidopsis thaliana - solanum lycopersicum - gastheer parasiet relaties - plantengroeiregulatoren - weerstand
    Root parasitic plant species such as broomrapes (Orobanche and Phelipanche spp.) and witchweeds (Striga spp.) are notorious agricultural weeds. They cause damage to crops by depriving them of water, nutrients and assimilates via a vascular connection. The difficulty in controlling root parasitic weeds is largely due to their intricate lifecycle and partially underground lifestyle. Their life cycle includes processes such as germination of the seed, the formation of the vascular connection with the host, the growth and development of the parasite after attachment and the emergence of shoots and flowers aboveground. The germination of many parasitic plants is induced by strigolactones that were recently shown to also be signalling compounds that stimulate mycorrhizal symbiosis. In addition, in the past few years, their role in plant development and plant defense has been established revealing them as a new class of plant hormones that exert their function likely in interaction with other hormones.
    Biosynthesis, regulation and biological role of strigolactones in rice
    Moura Luis Cardoso, C.S. De - \ 2014
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Carolien Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789462570917 - 166
    oryza sativa - rijst - striga - parasitaire planten - rizosfeer - lactonen - gigaspora rosea - biosynthese - oryza sativa - rice - striga - parasitic plants - rhizosphere - lactones - gigaspora rosea - biosynthesis

    In her thesis Catarina Cardoso studied strigolactone biosynthesis in rice. Strigolactones are multifunctional compounds produced by plants. They are plant hormones that regulate plant architecture, but in addition plants release strigolactones into the soil to communicate and initiate beneficial symbiosis with arbuscular mycorrhizal (AM) fungi. Parasitic plants of the genera Striga, Orobanche and Phelipanche take advantage of this communication to also recognize their hosts and infest them. These parasites infect crops and cause significant economic losses in Mediterranean regions and especially in Sub Saharan Africa where they put food security at risk. Catarina found there is large variation in strigolactone biosynthesis between the two major rice groups (indica and japonica) and located the genes responsible for this. She also showed that the different strigolactones produced by rice have a differential impact on AM fungi and seeds of parasitic plants. These findings suggest that it is possible to select crop varieties that can interact with AM fungi, without inducing parasitism. The knowledge generated in this study can contribute to the urgent need to control the worldwide parasitic weed problems. At the same time strigolactones also control plant development and the results of this study may resuylt in tools to develop better yielding and sustainable crops.

    Elucidation of strigolactone biosynthesis in the host plant rice and the signal perception in the parasitic plant Striga hermonthica
    Zhang, Y. - \ 2014
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Carolien Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789462570191 - 208
    striga hermonthica - parasitaire planten - biosynthese - signaaltransductie - oryza sativa - rijst - enzymen - plantenfysiologie - striga hermonthica - parasitic plants - biosynthesis - signal transduction - oryza sativa - rice - enzymes - plant physiology

    Strigolactones (SLs) are a newly identified class of plant hormones regulating plant architecture, including shoot and root branching. Plants also secrete blends of SLs into the rhizosphere, where they stimulate colonisation of the host roots by arbuscular mycorrhizal (AM) fungi, beneficial organisms for the host. But SLs also induce the seed germination of root parasitic plants, such as Striga, which can have a big negative impact on crop yield. A better insight in how the different SLs are synthesized by the host and how the parasitic plant Striga perceives them could help to develop crops with proper AM colonisation and Striga resistance at the same time. In this thesis, two cytochrome P450 enzymes responsible for the last step in SL formation and SL structural diversification in rice were identified. In addition, the F-Box protein MAX2 of Striga (ShMAX2), a SL signalling component, was characterised, representing the first example from a root parasitic plant species, which is paving the way for furthering our understanding of how SLs are perceived by these parasites. The knowledge gained in this thesis brings us a significant step closer to the possibility to improve crop breeding strategies for parasitic weed resistance.

    CAROTENOID CLEAVAGE DIOXYGENASE 7 modulates plant growth, reproduction, senescence, and determinate nodulation in the model legume Lotus japonicas
    Liu, J. ; Novero, M. ; Charnikhova, T. ; Ferrandino, A. ; Schubert, A. ; Ruyter-Spira, C.P. ; Biofante, P. ; Lovisolo, C. ; Bouwmeester, H.J. - \ 2013
    Journal of Experimental Botany 64 (2013)7. - ISSN 0022-0957 - p. 1967 - 1981.
    strigolactone analog gr24 - f-box protein - leaf senescence - germination stimulants - seed-germination - parasitic plants - key component - am fungi - arabidopsis - rice
    Strigolactones (SLs) are newly identified hormones that regulate multiple aspects of plant development, infection by parasitic weeds, and mutualistic symbiosis in the roots. In this study, the role of SLs was studied for the first time in the model plant Lotus japonicus using transgenic lines silenced for CAROTENOID CLEAVAGE DIOXYGENASE 7 (LjCCD7), the orthologue of Arabidopsis More Axillary Growth 3. Transgenic LjCCD7-silenced plants displayed reduced height due to shorter internodes, and more branched shoots and roots than the controls, and an increase in total plant biomass, while their root:shoot ratio remained unchanged. Moreover, these lines had longer primary roots, delayed senescence, and reduced flower/pod numbers from the third round of flower and pod setting onwards. Only a mild reduction in determinate nodule numbers and hardly any impact on the colonization by arbuscular mycorrhizal fungi were observed. The results show that the impairment of CCD7 activity in L. japonicus leads to a phenotype linked to SL functions, but with specific features possibly due to the peculiar developmental pattern of this plant species. It is believed that the data also link determinate nodulation, plant reproduction, and senescence to CCD7 function for the first time.
    The tomato CAROTENOID CLEAVAGE DIOXYGENASE8 (SlCCD8) regulates rhizosphere signaling, plant architecture and affects reproductive development through strigolactone biosynthesis
    Kohlen, W. ; Charnikhova, T. ; Lammers, M. ; Pollina, T. ; Toth, P. ; Haider, I. ; Pozo, M.J. ; Maagd, R.A. de; Ruyter-Spira, C.P. ; Bouwmeester, H.J. ; Lopez-Raez, J.A. - \ 2012
    New Phytologist 196 (2012)2. - ISSN 0028-646X - p. 535 - 547.
    arbuscular mycorrhizal fungi - tiller bud outgrowth - phosphate deficiency - parasitic plants - orobanche spp. - arabidopsis - gene - mutant - germination - rice
    •Strigolactones are plant hormones that regulate both above- and belowground plant architecture. Strigolactones were initially identified as rhizosphere signaling molecules. In the present work, the tomato (Solanum lycopersicum) CAROTENOID CLEAVAGE DIOXYGENASE 8 (SlCCD8) was cloned and its role in rhizosphere signaling and plant physiology assessed by generating knock-down lines. •Transgenic SlCCD8 plants were generated by RNAi-mediated silencing. Lines with different levels of strigolactone reduction – confirmed by UPLC-MS/MS – were selected and their phenotypes investigated. •Lines exhibiting reduced SlCCD8 levels displayed increased shoot branching, reduced plant height, increased number of nodes and excessive adventitious root development. In addition, these lines exhibited reproductive phenotypes such as smaller flowers, fruits, as well as fewer and smaller seeds per fruit. Furthermore, we show that strigolactone loading to the xylem sap is possibly restricted to orobanchol. •Infestation by Phelipanche ramosa was reduced by 90% in lines with a relatively mild reduction in strigolactone biosynthesis and secretion while arbuscular mycorrhizal symbiosis, apical dominance and fruit yield were only mildly affected. This demonstrates that reduction of strigolactone biosynthesis could be a suitable tool in parasitic weed management. Furthermore, our results suggest that strigolactones are involved in even more physiological processes than so far assumed.
    Genetic variation in strigolactone production and tillering in rice and its effect on Striga hermonthica infection
    Jamil, M. ; Charnikhova, T. ; Houshyani Hassanzadeh, B. ; Ast, A. van; Bouwmeester, H.J. - \ 2012
    Planta 235 (2012)3. - ISSN 0032-0935 - p. 473 - 484.
    arbuscular mycorrhizal fungi - parasitic plants - germination stimulants - phosphate deficiency - am fungi - sorghum - arabidopsis - signals - auxin - inhibition
    Tillering in cereals is a complex process in the regulation of which also signals from the roots in the form of strigolactones play an important role. The strigolactones are signalling molecules that are secreted into the rhizosphere where they act as germination stimulants for root parasitic plants and hyphal branching factors for arbuscular mycorrhizal fungi. On the other hand, they are also transported from the roots to the shoot where they inhibit tillering or branching. In the present study, the genetic variation in strigolactone production and tillering phenotype was studied in twenty rice varieties collected from all over the world and correlated with S. hermonthica infection. Rice cultivars like IAC 165, IAC 1246, Gangweondo and Kinko produced high amounts of the strigolactones orobanchol, 2'-epi-5-deoxystrigol and three methoxy-5-deoxystrigol isomers and displayed low amounts of tillers. These varieties induced high S. hermonthica germination, attachment, emergence as well as dry biomass. In contrast, rice cultivars such as Super Basmati, TN 1, Anakila and Agee displayed high tillering in combination with low production of the aforementioned strigolactones. These varieties induced only low S. hermonthica germination, attachment, emergence and dry biomass. Statistical analysis across all the varieties confirmed a positive correlation between strigolactone production and S. hermonthica infection and a negative relationship with tillering. These results show that genetic variation in tillering capacity is the result of genetic variation in strigolactone production and hence could be a helpful tool in selecting rice cultivars that are less susceptible to S. hermonthica infection.
    The relationship between strigolactones and Striga hermonthica infection in cereals
    Jamil, M. - \ 2012
    Wageningen University. Promotor(en): Harro Bouwmeester. - S.l. : s.n. - ISBN 9789461731388 - 184
    graansoorten - striga hermonthica - parasitaire planten - wortelexudaten - cereals - striga hermonthica - parasitic plants - root exudates

    Cereal production in Africa is under increasing constraint due to the obligate, out-crossing, hemiparasitic weed Striga hermonthica (Del.) Benth, a member of the Scrophulariaceae family. Striga parasitizes roots of cereals like sorghum, pearl millet, maize and upland rice. It has infested about 40% of the African agricultural land, resulting in severe yield losses or even complete crop failure worth US billion per annum. The subsistence farmers or approximately 300 million African people lose about 20-80% of their crop because of this weed. This considerable damage by Striga is due to the fact that existing control measures are often ineffective. Since much of the damage occurs underground during the early stages of parasitism, there is a need to develop control strategies that target the weed prior to attachment and emergence. A crucial step in the lifecycle of Striga is the induction of germination by strigolactones, signalling molecules secreted by the roots of its host. These strigolactones could be an important target to control this weed at the pre attachment phase. Control methods targeted at the germination and attachment phase, based on low strigolactones, might prove to be more effective and result in reduced infestation of this weed in cereal crops. In present thesis we studied the relationship between strigolactones and Striga infection in cereals and explored opportunities for lowering Striga damage at the germination or attachment phase. To this end different aspects like strigolactone biosynthetic inhibitors, genetic variation for strigolactone production, and the effect of fertilizers on strigolactone production were investigated in laboratory studies and – when possible - in the field in Kenya and Mali.

    The first investigation was on the use of carotenoid inhibitors to see the possibilities of strigolactone reduction in the roots of plants by blocking carotenoid biosynthesis. We postulated in this study that the (mild) inhibition of carotenoid biosynthesis by carotenoid inhibitors, could lead to a reduced production of strigolactones and decreased Striga germination and infection. Very low concentrations of four different carotenoid inhibitors (fluridone, norflurazon, clomazone and amitrole) were applied to rice either through irrigation or through foliar spray. Irrigation application of all carotenoid inhibitors and spray application of amitrole significantly decreased strigolactone production. Application of carotenoid inhibitors caused 61-75% reduction in Striga germination and 65-94% reduction in Striga attachment. The study shows thatthe reducing effect of carotenoid inhibitors (which, in much higher concentrations are widely used as herbicides) on strigolactone secretion and subsequent Striga germination and attachment may be developed into an attractive Striga control technology.

    Another experiment was aimed at assessing the pre-attachment Striga resistance based on low strigolactone production. We hypothesized that low strigolactones producing crop cultivars might possess pre-attachment Striga resistance due to less germination. For this purpose a set of 18 upland cultivars of NERICA and their parents were screened for strigolactones production and Striga infection parameters like germination, attachment, emergence and Striga dry biomass. NERICA 1 and CG14 produced significantly less strigolactones and showed less Striga infection while NERICAs 7, 8, 11 and 14 produced the highest amounts of strigolactones and showed the most severe Striga infection. This study shows that genetic variation for pre-attachment Striga resistance exists in NERICA rice due to variation in strigolactones. This could be highly relevant for breeding programs aimed at the development of Striga resistant cultivars. In another similar study we hypothesized that variation in strigolactone production in rice might be interconnected with the tillering phenotype and that this link could affect Striga infection. In this study the genetic variation was tested in a series of rice varieties collected from all over the world for strigolactone production, tillering phenotype and Striga infection. Rice cultivars like IAC 165, IAC 1246, Gangweondo and Kinko produced high amounts of the strigolactones, displayed low amounts of tillers and induced high Striga germination, attachment, emergence as well as Striga biomass. In contrast to this, rice cultivars such as Super Basmati, TN 1, Anakila and Agee showed low production of strigolactones and also low Striga germination and infection but high tillering. These results show that genetic variation in strigolactone production results in variation in tillering and also in Striga infection. The tillering phenotype could possibly be used as an easy indicator of the strigolactone production in a breeding programme for Striga resistance.

    Some experiments were also designed with the aim to quantify the relationship between strigolactones and Striga germination and attachment and to explore the mechanism responsible for the reported reduction in Striga parasitism in the field after fertilizer application. Different levels of nitrogen and phosphorous were applied under greenhouse conditions using rice, maize and sorghum. For maize and sorghum, a parallel study was carried out under field conditions in Kenya and Mali to study the translation of greenhouse results to the field. Application of N and P effectively suppressed Striga infection in the greenhouse in all three crop species and the reduction strongly correlated with reduced secretion of strigolactones into the rhizosphere and the Striga germination induced by these exudates. Although the field results with maize in Kenya were less consistent than in the greenhouse, especially with respect to P effect, still there was a trend that fertilizer application reduced Striga infection. These results show that the positive effect of fertilizer against Striga is at least partly due to a reduction in strigolactone production and as a consequence of that lower Striga germination and subsequent attachment.

    Overall it can be concluded that there is a good correlation between strigolactones andStriga germination, attachment and biomass. We found this using strigolactone biosynthesis inhibitors, genetic variation and using fertilizer application. These technologies can hence be exploited as an important tool to target Striga at a very early phase of its life cycle. The practical field application of these strategies requires further research but could lead to effective Striga control components that can be used in Integrated Striga Management.

    Strigolactones: a new musician in the orchestra of plant hormones
    Kohlen, W. ; Ruyter-Spira, C.P. ; Bouwmeester, H.J. - \ 2011
    Botany : an international journal for plant biology 89 (2011)12. - ISSN 1916-2790 - p. 827 - 840.
    arbuscular mycorrhizal fungi - root-system architecture - dependent auxin gradients - tiller bud outgrowth - arabidopsis-thaliana - phosphate starvation - apical-dominance - parasitic plants - cross-talk - phosphorus deficiency
    Strigolactones are known as germination stimulants for seeds of root parasitic plants of the Orobanchaceae and as the presymbiotic branching factor for arbuscular mycorrhizal fungi. They were also recently identified as a new class of plant hormones and have been the subject of many studies, leading to much advancement in our knowledge of how these molecules are involved in controlling plant development. In the first place, this concerns their role in the inhibition of shoot branching, but a number of studies have also revealed a role for strigolactones in shaping root system architecture or have suggested involvement of strigolactones in seed germination, hypocotyl elongation, and reproductive development. In all these studies, the interaction of strigolactones with other plant hormones such as auxin, abscisic acid, and ethylene is becoming clear. In this review we discuss the progress over the past 5 years in our understanding of the physiological role of strigolactones in the regulation of plant development. Keywords: strigolactones, plant horm
    Strigolactone Biosynthesis in Medicago truncatula and Rice Requires the Symbiotic GRAS-Type Transcription Factors NSP1 and NSP2
    Liu, W. ; Kohlen, W. ; Lillo, A. ; Camp, R. op den; Ivanov, S. ; Hartog, M. ; Limpens, E.H.M. ; Jamil, M. ; Smaczniak, C. ; Kaufmann, K. ; Yang, W.C. ; Hooiveld, G.J.E.J. ; Charnikhova, T. ; Bouwmeester, H.J. ; Bisseling, T. ; Geurts, R. - \ 2011
    The Plant Cell 23 (2011)10. - ISSN 1040-4651 - p. 3853 - 3865.
    arbuscular mycorrhizal fungi - affymetrix genechip data - tiller bud outgrowth - quality assessment - lotus-japonicus - germination stimulants - transduction pathway - phosphate deficiency - parasitic plants - red-clover
    Legume GRAS (GAI, RGA, SCR)-type transcription factors NODULATION SIGNALING PATHWAY1 (NSP1) and NSP2 are essential for rhizobium Nod factor-induced nodulation. Both proteins are considered to be Nod factor response factors regulating gene expression after symbiotic signaling. However, legume NSP1 and NSP2 can be functionally replaced by nonlegume orthologs, including rice (Oryza sativa) NSP1 and NSP2, indicating that both proteins are functionally conserved in higher plants. Here, we show that NSP1 and NSP2 are indispensable for strigolactone (SL) biosynthesis in the legume Medicago truncatula and in rice. Mutant nsp1 plants do not produce SLs, whereas in M. truncatula, NSP2 is essential for conversion of orobanchol into didehydro-orobanchol, which is the main SL produced by this species. The disturbed SL biosynthesis in nsp1 nsp2 mutant backgrounds correlates with reduced expression of DWARF27, a gene essential for SL biosynthesis. Rice and M. truncatula represent distinct phylogenetic lineages that split approximately 150 million years ago. Therefore, we conclude that regulation of SL biosynthesis by NSP1 and NSP2 is an ancestral function conserved in higher plants. NSP1 and NSP2 are single-copy genes in legumes, which implies that both proteins fulfill dual regulatory functions to control downstream targets after rhizobium-induced signaling as well as SL biosynthesis in nonsymbiotic conditions.
    Regulation of biosynthesis and transport of strigolactones and their effect on plant development
    Kohlen, W. - \ 2011
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Carolien Ruyter-Spira. - [S.l.] : S.n. - ISBN 9789461730145 - 192
    plantengroeiregulatoren - groeiremmers - plantenontwikkeling - plantenfysiologie - biosynthese - parasitaire planten - wortels - plant growth regulators - growth inhibitors - plant development - plant physiology - biosynthesis - parasitic plants - roots

    Strigolactonen zijn van carotenoïden afkomstige signaalmoleculen, aanvankelijk geïdentificeerd als de kiemstimulantia voor wortelparasieten van de Orobanchaceae familie en pre-symbiotisch signaal voor arbusculaire mycorrhiza (AM) schimmels. Strigolactonen zijn aangetoond in de wortelextracten en exudaten van diverse plantensoorten. Recent zijn strigolactonen - of hun afgeleiden - geïdentificeerd als plantenhormoon betrokken bij de regulatie van de plantarchitectuur. Het lijkt erop dat strigolactonen vooral in de wortels worden geproduceerd, maar de exacte plaats van strigolacton biosynthese is onbekend. Niettemin is het waarschijnlijk dat strigolactonen vanuit de wortels naar de scheut worden getransporteerd waar zij hun remmende werking op okselknopuitgroei, in samenwerking met auxine en cytokinines, uitoefenen. Tot nu toe zijn strigolactonen in de scheut van planten niet of nauwelijks aangetoond.

    Ook de biosynthese van strigolactonen is nog niet volledig opgehelderd. Een onbekend carotenoid substraat wordt opeenvolgend geknipt door CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7) en CAROTENOID CLEAVAGE DIOXYGENASE 8 (CCD8). Hiernaast, zijn twee enzymen, MORE AXILLARY GROWTH 1 (MAX1) and DWARF 27 (D27), betrokken bij de biosyntheses van strigolactonen, maar hun exacte rol is onbekend.

    In hoofdstuk 1, worden de wortelparasitaire planten van de Orobanchaceae familie en de problemen welke zij veroorzaken in de landbouw geïntroduceerd. Verder wordt de rol van strigolactonen in de levenscyclus van deze parasieten en in AM symbiose besproken. Daarnaast, wordt de recent ontdekte hormonale functie van strigolactonen in de plantarchitectuur, hun biosynthese, hormonale signalering en de twee gangbare theorieën over hoe strigolactonen een rol spelen bij apicale dominantie beschreven.

    Van 5-deoxystrigol wordt gedacht dat dit het eerste echte strigolacton afkomstig van de strigolacton biosynthese route is. Aangenomen wordt dat 5-deoxystrigol via een aantal - al dan niet enzymatische - stappen de precursor is voor alle andere bekende strigolactonen. In hoofdstuk 2, wordt de biosynthese van solanacol in de wortel van tomaat (Solanum lycopersicum) beschreven. Solanacol heeft een aromatische A-ring en daardoor is de biosyntheses van dit strigolactone via 5-deoxystrigol niet voor de hand liggend. Op basis van de aanwezigheid van andere strigolactonen in tomaat (orobanchol, orobanchyl acetate, twee 7-hydroxy-orobanchol isomeren, 7-oxo-orobanchol en vier didehydro-orobanchol isomeren) speculeren wij hoe solanacol door een series van enzymatische hydroxylatie-dehydroxylatie reacties, de migratie van een methyl groep en de introductie van dubbele bindingen van 5-deoxystrigol afgeleid kan zijn.

    In hoofdstuk 3bespreken we de klonering van een tomaat CAROTENOID CLEAVAGE DIOXYGENASE 8(SlCCD8) en demonsteren dat een reductie in CCD8 expressie leid tot een reductie van strigolactonen in de wortel extracten, exudaten en het xyleem sap. Alle lijnen tonen excessieve zijscheutgroei, zijn korter en hebben meer internodes. Ook demonstreren wij dat de sterkte van al deze fenotypes correleert met de concentratie orobanchol in het xyleem sap. Verder tonen we aan dat een milde reductie in strigolacton biosynthese en de gerelateerde secretie naar de rhizosphere voldoende is om parasitisme door Phelipanche ramosa met 90% te verminderen. Dit zonder de apicale dominantie of AM symbiose te sterk nadelig te beïnvloeden. Verder melden we enkele additionele fenotypes in de reproductieve ontwikkeling van tomaat (zoals kleinere bloemen, vruchten en zaden) - normaliter geassocieerd met gereduceerde auxine niveaus. We demonstreren verlaagde niveaus van vrij auxine in deze organen, wat er op wijst dat deze fenotypes mogelijk een consequentie zijn van het ontbreken van het regulerende effect van strigolactonen op het auxine niveau.

    Het goed beschreven plant hormoon abscissine zuur (ABA) is net als de strigolactonen afkomstig van de carotenoïden. Eerdere experimenten binnen onze groep wezen uit dat een mutatie in 9-cis-epoxycarotenoid dioxygenase (NCED) – een sleutel enzym betrokken bij de ABA biosyntheses – leidt tot een reductie in de strigolacton productie. Dit gaf aanleiding tot onderzoek naar de relatie tussen ABA en strigolactonen. De resultaten van dit onderzoek worden omschreven in hoofdstuk 4. Wij demonstreren dat applicatie van de carotenoid cleavage dioxygenase (CCD) inhibitor D2 het strigolacton niveau verlaagt, maar geen effect heeft op de ABA concentraties. Echter, in planten behandeld met abamineSG – een remmer van de 9-cis-epoxycarotenoid dioxygenases (NCEDs) - en in de ABA deficiënte mutanten notabilis, sitiens en flacca (mutanten in twee verschillende enzymatische stappen van de ABA biosynthese), zijn de niveaus van zowel ABA als strigolactonen gereduceerd. Onze resultaten duiden op een correlatie tussen ABA niveaus en strigolacton biosynthese en wijzen op een mogelijke rol van ABA in de regulatie van strigolacton biosynthese.

    In hoofdstuk 5wordt de rol van twee GRAS-type transcriptie factoren (NSP1 en NSP2) in de regulatie van strigolacton biosynthese besproken. In peulvruchten hebben deze transcriptie factoren een essentiële rol in de door Rhizobium Nod factor geïnduceerde nodulatie. In dit hoofdstuk tonen we aan dat NSP1 en NSP2 ook vereist zijn voor de strigolactone biosynthese in Medicago truncatula (Medicago) enrijst. Hiervoor is Medicago opgezet als een modelplant voor stigolacton analyse. Ook tonen wij aan dat het strigolactonenmengsel van M. truncatulabestaat uit dedihydro-orobanchol (major) en orobanchol (minor). In dit werk identificeren we voor het eerst transcriptie factoren welke de biosynthese van strigolactonen reguleren. Wij tonen aan dat NSP1 de strigolacton biosynthese reguleert door middel van de regulatie van de expressie van D27. Een in vitro binding studie toont dat MtD27 eenprimair doel van MtNSP1 kan zijn. Verder tonen wij aan dat MtNSP2 essentieel is voor de conversie van orobanchol naar dedihydro-orobanchol. Het feit dat NSP1 en NSP2 vereist zijn voor strigolacton biosynthese in zowel rijst als Medicago - soorten die twee verschillende fylogenetische geslachten vertegenwoordigen welke ongeveer 150 miljoen jaar geleden ontstaan zijn – brengt ons tot de aanname dat de regulatie van de strigolacton biosynthese door NSP1 en NSP2 als een voorouderlijke functie in hogere planten is geconserveerd.

    In hoofdstuk 6bestuderen we strigolacton biosynthese in Arabidopsis thaliana (Arabidopsis). Strikte controle van de groeicondities en optimalisatie van de analytische protocollen voor strigolacton analyse maakte de detectie van orobanchol, orobanchyl acetaat en 5-deoxystrigol in Arabidopsis mogelijk. In dit hoofdstuk tonen wij aan dat de relatie tussen fosfaat tekort en de inductie van strigolacton biosynthes ook in deze soort aanwezig is. Dat is opmerkelijk omdat Arabidopsis geen AM symbiose aangaat in tegenstelling tot de meeste andere landplanten. Het ontbreken van AM symbiose in Arabidopsis is daarom mogelijk een verloren eigenschap. Wij speculeren dat de exudatie van strigolactonen naar de rhizosfeer – wat Arabidopsis zij het in lage hoeveelheden nog steeds doet - een overblijfsel is van deze voorouderlijke eigenschap welke door Arabidopsis verloren is. Echter, onze resultaten demonstreren dat de verhoging van de strigolacton biosynthese in Arabidopsis onder fosfaat tekort dient om de groei van de zijscheuten te verminderen onder deze suboptimale condities. Wij speculeren dat dit mogelijk een evolutionair voordeel schept welke de nieuwe stuwende kracht is voor het behoud van fosfaat-tekort geïnduceerde verhoging van de strigolacton biosynthese in Arabidopsis, aangezien AM symbiose niet meer aanwezig is.We tonen aan dat orobanchol getransporteerd wordt in het xyleem sap en dat de concentratie hiervan omhoog gaat onder fosfaat tekort. Verder leveren we analytisch bewijs dat MAX1 is vereist voor de biosynthese van orobanchol.

    Een nieuwe functie van strigolactonen in de regulatie van wortelarchitectuur in tomaat en Arabidopsis is recent ontdekt. In hoofdstuk 7tonen we dat een reductie in strigolacton biosynthese en/of perceptie - als vertoond in de max1,2,4 mutanten - leidt tot een reductie in de lengte van het primaire wortelmeristeem. We demonstreren dat toediening van het synthetische strigolacton GR24 dit fenotype in alle max mutanten - uitgezonderd de strigolacton ongevoelige mutant max2 – kan herstellen.De toediening van GR24 onder toereikende fosfaat condities reduceert het totale aantal laterale wortels per plant - hun ontwikkeling wordt gestopt in fase vijf van de laterale wortel primordium initiatie. Ook tonen wij aan dat hogere concentraties GR24 de initiatie van deze laterale wortel primordia compleet blokkeren wat leidt tot het instorten van het primaire wortelmeristeem.Echter, als GR24 samen met exogeen auxine (NAA) wordt toegediend heeft het een stimulerend effect op de laterale wortelontwikkeling en -uitgroei. Daaraan analoog, onder fosfaatbeperkende condities stimuleert de verhoging van endogene strigolacton niveaus (hoofdstuk 6) in wild type planten een snellere uitgroei van laterale wortel primordia vergeleken met de strigolacton-deficiënte mutanten. Verder demonstreren wij dat – onder toereikende fosfaat condities - GR24 toediening aan het wortelsysteem van Arabidopsis leidt tot een lagere auxineconcentratie in de bladeren. Gecombineerd wijzen deze resultaten erop dat strigolactonen lokale auxine gradiënten modificeren en zo invloed uitoefenen op de wortel architectuur. Daardoor zal het netto resultaat van de strigolactone werking op de ontwikkeling van het wortelstelsel afhangen van de auxine status van een plant. Wij denken dat een uiterst fijn gereguleerde balans tussen auxine en strigolactonen de basis vormt voor het mechanisme dat de wortel-scheut ratio van een plant reguleert, bijvoorbeeld onder fosfaat limiterende condities.

    Hoofdstuk 8is een samenvatting en discussie van de meest belangrijke resultaten verkregen gedurende het werk gepresenteerd in dit proefschrift. Er wordt getracht de nieuw verkregen kennis te integreren met de huidige kennis van strigolactonen. Zowel op het gebied van hun hormonale eigenschappen als hun rol als rhizosfeer signaal. In dit hoofdstuk word verder vooruit gekeken naar de perspectieven van het onderzoek aan strigolactonen. Speciale aandacht wordt besteed aan de relatie met het probleem van de parasitaire planten.

    Strigolactones are transported through the xylem and play a key role in shoot architectural response to phosphate deficiency in nonarbuscular mycorrhizal host Arabidopsis
    Kohlen, W. ; Charnikhova, T. ; Qing, L. ; Bours, R.M.E.H. ; Domagalska, M. ; Beguerie, S. ; Verstappen, F.W.A. ; Leyser, O. ; Bouwmeester, H.J. ; Ruyter-Spira, C.P. - \ 2011
    Plant Physiology 155 (2011)2. - ISSN 0032-0889 - p. 974 - 987.
    root-system architecture - germination stimulants - seed-germination - parasitic plants - indole-3-acetic-acid levels - phosphorus deficiency - auxin transport - orobanche spp. - rms1 mutant - am fungi
    The biosynthesis of the recently identified novel class of plant hormones, strigolactones, is up-regulated upon phosphate deficiency in many plant species. It is generally accepted that the evolutionary origin of strigolactone up-regulation is their function as a rhizosphere signal that stimulates hyphal branching of arbuscular mycorrhizal fungi. In this work, we demonstrate that this induction is conserved in Arabidopsis (Arabidopsis thaliana), although Arabidopsis is not a host for arbuscular mycorrhizal fungi. We demonstrate that the increase in strigolactone production contributes to the changes in shoot architecture observed in response to phosphate deficiency. Using high-performance liquid chromatography, column chromatography, and multiple reaction monitoring-liquid chromatography-tandem mass spectrometry analysis, we identified two strigolactones (orobanchol and orobanchyl acetate) in Arabidopsis and have evidence of the presence of a third (5-deoxystrigol). We show that at least one of them (orobanchol) is strongly reduced in the putative strigolactone biosynthetic mutants more axillary growth1 (max1) and max4 but not in the signal transduction mutant max2. Orobanchol was also detected in xylem sap and up-regulated under phosphate deficiency, which is consistent with the idea that root-derived strigolactones are transported to the shoot, where they regulate branching. Moreover, two additional putative strigolactone-like compounds were detected in xylem sap, one of which was not detected in root exudates. Together, these results show that xylem-transported strigolactones contribute to the regulation of shoot architectural response to phosphate-limiting conditions.
    Arbuscular mycorrhizal symbiosis decreases strigolactone production in tomato.
    Lopez Raez, J.A. ; Charnikhova, T. ; Fernandez, I. ; Bouwmeester, H.J. ; Pozo, M.J. - \ 2011
    Journal of Plant Physiology 168 (2011)3. - ISSN 0176-1617 - p. 294 - 297.
    parasitic plants - fungi - infection - biosynthesis - inhibition - signals - roots - acid
    Strigolactones are a new class of plant hormones emerging as important signals in the control of plant architecture. In addition, they are key elements in plant communication with several rhizosphere organisms. Strigolactones are exuded into the soil, where they act as host detection signals for arbuscular mycorrhizal (AM) fungi, but also as germination stimulants for root parasitic plant seeds. Under phosphate limiting conditions, plants up-regulate the secretion of strigolactones into the rhizosphere to promote the formation of AM symbiosis. Using tomato as a model plant, we have recently shown that AM symbiosis induces changes in transcriptional and hormonal profiles. Using the same model system, here we analytically demonstrate, using liquid chromatography–tandem mass spectrometry, that strigolactone production is also significantly reduced upon AM symbiosis. Considering the dual role of the strigolactones in the rhizosphere as signals for AM fungi and parasitic plants, we discuss the potential implications of these changes in the plant interaction with both organisms.
    Does abscisic acis affect strigolactone biosynthesis?
    Lopez-Raez, J.A. ; Kohlen, W. ; Charnikhova, T. ; Mulder, P.P.J. ; Undas, A.K. ; Sergeant, J. ; Verstappen, F. ; Bugg, T.D.H. ; Thompson, A.J. ; Ruyter-Spira, C.P. ; Bouwmeester, H.J. - \ 2010
    New Phytologist 187 (2010)2. - ISSN 0028-646X - p. 343 - 354.
    arbuscular mycorrhizal fungi - parasitic plants - germination stimulants - arabidopsis-thaliana - phosphorus stress - mutant notabilis - orobanche spp. - tomato plants - water-stress - wild-type
    Strigolactones are considered a novel class of plant hormones that, in addition to their endogenous signalling function, are exuded into the rhizosphere acting as a signal to stimulate hyphal branching of arbuscular mycorrhizal (AM) fungi and germination of root parasitic plant seeds. Considering the importance of the strigolactones and their biosynthetic origin (from carotenoids), we investigated the relationship with the plant hormone abscisic acid (ABA). Strigolactone production and ABA content in the presence of specific inhibitors of oxidative carotenoid cleavage enzymes and in several tomato ABA-deficient mutants were analysed by LC-MS/MS. In addition, the expression of two genes involved in strigolactone biosynthesis was studied. The carotenoid cleavage dioxygenase (CCD) inhibitor D2 reduced strigolactone but not ABA content of roots. However, in abamineSG-treated plants, an inhibitor of 9-cis-epoxycarotenoid dioxygenase (NCED), and the ABA mutants notabilis, sitiens and flacca, ABA and strigolactones were greatly reduced. The reduction in strigolactone production correlated with the downregulation of LeCCD7 and LeCCD8 genes in all three mutants. The results show a correlation between ABA levels and strigolactone production, and suggest a role for ABA in the regulation of strigolactone biosynthesis.
    Bias and conflict in phylogenetic inference of myco-heterotrophic plants: a case study in Thismiaceae
    Merckx, V. ; Bakker, F.T. ; Huysmans, K. ; Smets, B.F. - \ 2009
    Cladistics-The International Journal of the Willi Hennig Society 25 (2009)1. - ISSN 0748-3007 - p. 64 - 77.
    long-branch attraction - 18s rdna sequences - parasitic plants - nucleotide substitution - flowering plants - tree selection - molecular-data - gene-transfer - data sets - burmanniaceae
    Due to morphological reduction and absence of amplifiable plastid genes, the identification of photosynthetic relatives of heterotrophic plants is problematic. Although nuclear and mitochondrial gene sequences may offer a welcome alternative source of phylogenetic markers, the presence of rate heterogeneity in these genes may introduce bias/systematic error in phylogenetic analyses. We examine the phylogenetic position of Thismiaceae based on nuclear 18S rDNA and mitochondrial atpA DNA sequence data, as well as using parsimony, likelihood and Bayesian inference methods. Significant differences in evolutionary rates of these genes between closely related taxa lead to conflicting results: while parsimony analyses of 18S rDNA and combined data strongly support the monophyly of Thismiaceae, Bayesian inference, with and without a relaxed molecular clock, as well as the Swofford-Olsen-Waddell-Hillis (SOWH) test confidently reject this hypothesis. We show that rate heterogeneity in our data leads to long-branch attraction artifacts in parsimony analysis. However, using model-based inference methods the question of whether Thismiaceae are monophyletic remains elusive. On the one hand maximum likelihood nonparametric bootstrapping and parametric hypothesis tests fail to support a paraphyletic Thismiaceae, on the other hand Bayesian inference methods (both without and with a relaxed clock) significantly reject a monophyletic Thismiaceae. These results show that an adequate sampling, the use of rate homogeneous data, and the application of different inference methods are important factors for developing phylogenetic hypotheses of myco-heterotrophic plants
    Susceptibility of the Tomato Mutant High Pigment-2dg (hp-2dg) to Orobanche spp. Infection
    Lopez Raez, J.A. ; Charnikhova, T. ; Mulder, P.P.J. ; Kohlen, W. ; Bino, R.J. ; Levin, I. ; Bouwmeester, H.J. - \ 2008
    Journal of Agricultural and Food Chemistry 56 (2008)15. - ISSN 0021-8561 - p. 6326 - 6332.
    arbuscular mycorrhizal fungi - striga-hermonthica - parasitic plants - resistance - germination - roots - strigolactones - biosynthesis - biogenesis - genotypes
    The consumption of natural products with potential health benefits has been continuously growing, and enhanced pigmentation is of major economic importance in fruits and vegetables. The tomato hp-2dg is an important mutant line that has been introgressed into commercial tomato cultivars marketed as lycopene rich tomatoes (LRT) because of their enhanced fruit pigmentation, attributed to higher levels of carotenoids, including lycopene. Strigolactones are signaling compounds that mediate host finding in root parasitic plants and are biosynthetically derived from carotenoids. Considering the high carotenoid content of the hp-2dg mutant, we studied its susceptibility to the root parasite Orobanche. In a field experiment, the average number of Orobanche aegyptiaca plants growing on hp-2dg was surprisingly significantly reduced compared with its isogenic wild-type counterpart. In vitro assays and LC-MS/MS analysis showed that this reduction was associated with a lower production of strigolactones, which apparently renders the high-carotenoid hp-2dg mutant less susceptible to Orobanche
    Ondergrondse communicatie: de driehoeksrelatie gastheerplant, parasitaire plant en mycorrhiza-schimmel
    Kohlen, W. ; Bouwmeester, H.J. - \ 2007
    Gewasbescherming 38 (2007)4. - ISSN 0166-6495 - p. 145 - 149.
    detectie - zintuiglijke waarneming - waardplanten - parasitaire planten - striga - mycorrhizaschimmels - scrophulariales - interacties - plantenvoeding - wortels - bodemflora - symbiose - detection - organolepsis - host plants - parasitic plants - striga - mycorrhizal fungi - scrophulariales - interactions - plant nutrition - roots - soil flora - symbiosis
    De ontdekking van strigolactonen laat zien dat planten op grote schaal ondergronds communiceren. Planten produceren die strigolactonen niet om te communiceren met de parasitaire planten, maar met de mycorrhiza schimmels en mogelijk ook andere voor de plant nuttige organismen. De parasitaire planten hebben een mechanisme ontwikkeld om deze communicatie af te luisteren en te gebruiken in hun eigen voordeel. Om het grote belang van deze stoffen verder te onderzoeken heeft Harro Bouwmeester begin 2006 van NWO een Vici-fellowship ontvangen ter waarde van 1.2 miljoen euro. Met een onderzoeksgroep, waartoe ook auteur Wouter Kohlen behoort, probeert hij de genen in kaart te brengen die zijn betrokken bij de productie van strigolactonen en inzicht te krijgen in hoe ze gereguleerd worden. Ook wil het team weten hoe de strigolactonen worden waargenomen door de parasitaire planten en hoe deze stoffen de interactie tussen de gastheer en beide bezoekers - parasitaire planten en mycorrhiza schimmels - reguleren. De bedoeling is dat het onderzoek niet alleen het begrip zal verbeteren van hoe gastheren communiceren met mycorrhiza schimmels en parasitaire planten, maar ook zal bijdragen aan het verminderen van een reusachtig probleem in Afrika, waar in vele landen Striga de oorzaak is van catastrofale oogstverliezen
    Striga hermonthica seed bank dynamics: process quantification and modelling
    Mourik, T.A. van - \ 2007
    Wageningen : Wageningen University and Research Centre (Tropical Resource Management Papers 92) - ISBN 9789085851295 - 123
    striga hermonthica - parasitic plants - parasitic weeds - weed control - integrated pest management - seed banks - buried seeds - dynamics - sorghum - millets - mali - niger - striga hermonthica - parasitaire planten - parasitaire onkruiden - onkruidbestrijding - geïntegreerde plagenbestrijding - zaadbanken - begraven zaden - dynamica - sorghum - gierst - mali - niger
    Nieuwe inzichten in de interactie tussen sorghum en het parasitaire onkruid Striga hermontica
    Ast, A. van - \ 2006
    Gewasbescherming 37 (2006)6. - ISSN 0166-6495 - p. 275 - 278.
    striga hermonthica - parasitaire planten - striga - orobanchaceae - waardplanten - sorghum - graansoorten - ziektebestrijdende teeltmaatregelen - onkruidbestrijding - cultuurmethoden - bodemvruchtbaarheid - gewasbescherming - afrika - striga hermonthica - parasitic plants - striga - orobanchaceae - host plants - sorghum - cereals - cultural control - weed control - cultural methods - soil fertility - plant protection - africa
    Striga hermonthica (Del.) Benth. is een parasitaire plant uit de Orobanchaceae familie. De soort komt van oorsprong voor in Afrika en hecht zich aan de wortels van belangrijke voedselgewassen als maïs, sorghum, gierst en rijst. In grote delen van Afrika heeft Striga zich ontwikkeld tot de belangrijkste groeireducerende factor. Veelvuldig is waargenomen dat de problemen met Striga toenemen wanneer de bodemvruchbaarheid afneemt
    The influence of time and severity of Striga infection on the Sorghum bicolor - Striga hermonthica association
    Ast, A. van - \ 2006
    Wageningen University. Promotor(en): Martin Kropff, co-promotor(en): Lammert Bastiaans. - Wageningen : s.n. - ISBN 9789085043997 - 154
    striga hermonthica - striga - parasitaire planten - onkruiden - sorghum bicolor - sorghum - infectie - aantasting - onkruidbestrijding - plantenecologie - ecofysiologie - striga hermonthica - striga - parasitic plants - weeds - sorghum bicolor - sorghum - infection - infestation - weed control - plant ecology - ecophysiology
    Keywords: Striga hermonthica , Sorghum bicolor , infection time, infection level, tolerance.

    This thesis presents the results of a study on the interaction between the parasitic weed Strigahermonthica (Del.) Benth. and sorghum ( Sorghum bicolor [L.] Moench). The main objective of the study was to investigate the effects of time and level of Striga infection on the interaction between host plant and parasite. Consequences for sorghum performance and the growth and development of the parasite were examined. A comparison between two sorghum cultivars differing in level of Striga tolerance, revealed that the absence of a negative effect of Striga infection on photosynthetic rate and a delayed time of first Striga infection both contributed to the lower extent of yield reduction of the tolerant cultivar. Likewise, in an experiment with a wide range of Striga seed infestation levels, it was observed that higher soil infestations levels did not only result in a higher Striga infection level, but also in an advanced time of first Striga infection.The importance of time of infection was further investigated in a pot experiment in which the time of infection was artificially delayed.Striga parasitism and reproduction, and the detrimental effects of Striga on crop performance could be strongly reduced by delaying the time of first infection. Prospects of reducing Striga parasitism by means of cultural control methods that are based on the principle of a delayed onset of Striga attachment were assessed. In a pot experiment, the combination ofshallow soil tillage, deep planting and the use of transplantsresulted in a four-week delay in first emergence of the parasite, a strongly reduced infection level of the sorghum host and highly improved sorghum yields. Evaluation of these methods under field conditions resulted in a 85% reduction in Striga -infection level, but as no delay in time of parasite infection was established, no beneficial effect on crop yield was obtained. Potential causes of the absence of a delay in Striga infection time under field conditions were discussed and alternative options for establishing a delayed infection in the field were proposed.
    The influence of time and severity of Striga infection on the Sorghum bicolor - Striga hermonthica association
    Ast, A. van - \ 2006
    Wageningen : Wageningen University and Research Centre (Tropical resource management papers no. 77) - ISBN 9789085850588 - 154
    striga hermonthica - striga - parasitaire planten - onkruiden - sorghum bicolor - sorghum - infectie - aantasting - onkruidbestrijding - plantenecologie - ecofysiologie - striga hermonthica - striga - parasitic plants - weeds - sorghum bicolor - sorghum - infection - infestation - weed control - plant ecology - ecophysiology
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