What drives fruit growth?
Okello, R.C. ; Heuvelink, E. ; Visser, P.H.B. de; Struik, P.C. ; Marcelis, L.F.M. - \ 2015
Functional Plant Biology 42 (2015)9. - ISSN 1445-4408 - p. 817 - 827.
individual cucumber fruits - tomato fruit - cell-size - lycopersicon-pimpinellifolium - dna endoreduplication - carbon availability - hormone-levels - qtl detection - plant fruit - organ size
Cell division, endoreduplication (an increase in nuclear DNA content without cell division) and cell expansion are important processes for growth. It is debatable whether organ growth is driven by all three cellular processes. Alternatively, all could be part of a dominant extracellular growth regulatory mechanism. Cell level processes have been studied extensively and a positive correlation between cell number and fruit size is commonly reported, although few positive correlations between cell size or ploidy level and fruit size have been found. Here, we discuss cell-level growth dynamics in fruits and ask what drives fruit growth and during which development stages. We argue that (1) the widely accepted positive correlation between cell number and fruit size does not imply a causal relationship; (2) fruit growth is regulated by both cell autonomous and noncell autonomous mechanisms as well as a global coordinator, the target of rapamycin; and (3) increases in fruit size follow the neocellular theory of growth.
Genotype-by-temperature interactions may help to maintain clonal diversity in asterionella formosa (Bacillariophyceae)
Gsell, A.S. ; Domis, L.N.D. ; Przytulska-Bartosiewicz, A. ; Mooij, W.M. ; Donk, E. van; Ibelings, B.W. - \ 2012
Journal of Phycology 48 (2012)5. - ISSN 0022-3646 - p. 1197 - 1208.
diatom ditylum-brightwellii - fresh-water phytoplankton - reaction norms - phenotypic plasticity - genetic-variation - centric diatom - cell-size - environment interactions - marine-phytoplankton - skeletonema-costatum
Marine and freshwater phytoplankton populations often show large clonal diversity, which is in disagreement with clonal selection of the most vigorous genotype(s). Temporal fluctuation in selection pressures in variable environments is a leading explanation for maintenance of such genetic diversity. To test the influence of temperature as a selection force in continually (seasonally) changing aquatic systems we carried out reaction norms experiments on co-occurring clonal genotypes of a ubiquitous diatom species, Asterionella formosa Hassall, across an environmentally relevant range of temperatures. We report within population genetic diversity and extensive diversity in genotype-specific reaction norms in growth rates and cell size traits. Our results showed genotype by environment interactions, indicating that no genotype could outgrow all others across all temperature environments. Subsequently, we constructed a model to simulate the relative proportion of each genotype in a hypothetical population based on genotype and temperature-specific population growth rates. This model was run with different seasonal temperature patterns. Our modeling exercise showed a succession of two to several genotypes becoming numerically dominant depending on the underlying temperature pattern. The results suggest that (temperature) context dependent fitness may contribute to the maintenance of genetic diversity in isolated populations of clonally reproducing microorganisms in temporally variable environments.
A Caenorhabditis elegans Wild Type Defies the Temperature-Size Rule Owing to a Single Nucleotide Polymorphism in tra-3
Kammenga, J.E. ; Doroszuk, A. ; Riksen, J.A.G. ; Hazendonk, E. ; Spiridon, L.N. ; Petrescu, A.J. ; Tijsterman, M. ; Plasterk, R.H.A. ; Bakker, J. - \ 2007
Plos Genetics 3 (2007)3. - ISSN 1553-7404
quantitative trait loci - secondary structure prediction - life-history puzzle - drosophila-melanogaster - body-size - cell-size - c-elegans - transcription factor - sex-determination - cold-acclimation
Ectotherms rely for their body heat on surrounding temperatures. A key question in biology is why most ectotherms mature at a larger size at lower temperatures, a phenomenon known as the temperature¿size rule. Since temperature affects virtually all processes in a living organism, current theories to explain this phenomenon are diverse and complex and assert often from opposing assumptions. Although widely studied, the molecular genetic control of the temperature¿size rule is unknown. We found that the Caenorhabditis elegans wild-type N2 complied with the temperature¿size rule, whereas wild-type CB4856 defied it. Using a candidate gene approach based on an N2 × CB4856 recombinant inbred panel in combination with mutant analysis, complementation, and transgenic studies, we show that a single nucleotide polymorphism in tra-3 leads to mutation F96L in the encoded calpain-like protease. This mutation attenuates the ability of CB4856 to grow larger at low temperature. Homology modelling predicts that F96L reduces TRA-3 activity by destabilizing the DII-A domain. The data show that size adaptation of ectotherms to temperature changes may be less complex than previously thought because a subtle wild-type polymorphism modulates the temperature responsiveness of body size. These findings provide a novel step toward the molecular understanding of the temperature¿size rule, which has puzzled biologists for decades.