An alternative bioassay for Synchytrium endobioticum demonstrates the expression of potato wart resistance in aboveground plant parts
Vossenberg, Bart van de; Gent-Pelzer, Marga van; Boerma, M. ; Gouw, Lucas P. van der; Lee, Theo van der; Vossen, Jack - \ 2019
Wageningen University and Research
PRJEB30662 - ERP113139 - Synchytrium endobioticum
The obligate biotrophic chytrid species Synchytrium endobioticum is the causal agent of potato wart disease. Currently 39 pathotypes have been described based on their interaction with a differential set of potato varieties. Wart resistance and pathotyping is performed using bioassays in which etiolated tuber sprouts are inoculated. Here we describe an alternative method in which aboveground plant parts are inoculated. Susceptible plants produced typical wart symptoms in developing, but not in fully expanded, aboveground organs. Colonization of the host by S endobioticum was verified by screening for resting spores by microscopy and by molecular techniques using TaqMan PCR and RNAseq analysis. When applied to resistant plants, none of these symptoms were detectable. Recognition of S. endobioticum pathotypes by differentially resistant potato varieties was identical in aboveground plant parts and the tuber-based bioassays. This suggests that S. endobioticum resistance genes are expressed both in etiolated “belowground” sprouts and green aboveground organs. RNAseq analysis demonstrated that the symptomatic aboveground materials contain less contaminants compared to resting spores extracted from tuber-based assays. This reduced microbial contamination in the aboveground bioassay could be an important advantage to study this obligate biotrophic plant-pathogen interaction. As wart resistance is active in both below and above ground organs, the aboveground bioassay can potentially speed up screening for S. endobioticum resistance in potato breeding programs as it omits the requirement for tuber formation. In addition, possibilities arise to express S. endobioticum effectors in potato leaves through agroinfiltration, thereby providing additional phenotyping tools for research and breeding.
The linear mitochondrial genome of the quarantine chytrid Synchytrium endobioticum; insights into the evolution and recent history of an obligate biotrophic plant pathogen
Vossenberg, Bart van de; Brankovics, Balázs ; Nguyen, H.D.T. ; Gent-Pelzer, Marga van; Smith, D. ; Przetakiewicz, J. ; Kreuze, J.F. ; Boerma, M. ; Leeuwen, G.C.M. van; André Lévesque, C. ; Lee, Theo van der - \ 2018
Wageningen University and Research
PRJEB24465 - ERP106293 - Synchytrium endobioticum
Species of the Chytridiomycota, also known as chytrids, belong to a basal lineage in the fungal kingdom inhabiting terrestrial and aquatic environments. Most of the described chytrids are free-living saprophytes, but several species cause important diseases. Examples are Batrachochytrium dendrobatidis responsible for the world wide amphibian decline and Synchytrium endobioticum the causal agent of potato wart disease. Synchytrium endobioticum has an obligate biotrophic lifestyle and isolates can be differentiated based on their virulence on a differential set of potato cultivars, referred to as pathotypes. Quarantine measures have been implemented worldwide to control the disease and to prevent its spread. To determine taxonomical relationships, and to gain insights into the evolution and recent history of introductions of this plant pathogen we assembled and annotated the complete mitochondrial genome of S. endobioticum and generated mitochondrial genomes for five additional chytrid species. The mitochondrial genome of S. endobioticum pathotype 1(D1) strain MB42 is a linear 72,865 bp molecule with terminal inverted repeats that encodes 14 core genes typically found on fungal mitochondrial genomes. Based on single nucleotide polymorphisms the 30 S. endobioticum isolates sequenced could be clustered in four distinct mitochondrial lineages, indicating multiple introductions of the pest to the European main land. These lineages comprise different pathotypes suggesting that pathotypes 2(G1) and 6(O1) have emerged at least twice independently. Variations for polymorphic sites within a strain were observed demonstrating that S. endobioticum strains represent in fact a community of different genotypes. Such a community was shown to be complex and stable over time, but we also demonstrate that the population may shift rapidly based on selection for virulence on a specific R gene from the host.