Endopolyploidy and fitness compensation following herbivory in globally-distributed ecotypes and cell-cycle mutant lines

Background/Question/Methods

Endoreduplication is an important process in the maturation of cells, where an increase in cellular ploidy via repeated DNA replications without mitosis increases cell size and thus aids in the expansion and differentiation of the cell. Previous studies have demonstrated a correlation between the generation of endopolyploidy by endoreduplication and fitness compensation of plants following the removal of apical dominance by herbivory, where an increase in cellular ploidy throughout the plant is associated with increased seed and silique production in Arabidopsis thaliana Columbia, while a lower prevalence of endoreduplication in Landsberg erecta is associated with equal siliques and fewer seeds. A linear trend was also present in a Columbia x Landsberg erecta cross producing recombinant inbred lines. Here, using flow cytometry to measure cellular ploidy, we investigated this trend in globally distributed, genetically disparate populations of Arabidopsis thaliana to test the generalizability of the correlation between endoreduplication and fitness compensation following herbivory. Further, by knocking out and overexpressing ILP1, a gene that regulates endoreduplication, we directly manipulated endoreduplication in the Columbia ecotype to determine if there is a direct causal link between endoreduplication and fitness compensation.

Results/Conclusions

We report that there is a linear trend between endoreduplication and fitness compensation in globally distributed ecotypes of Arabidopsis thaliana, where increasing cellular ploidy by endoreduplication was positively associated with measures of fitness (silique and seed production). The persistence of the trend despite the inclusion of greater genetic diversity further supports the general correlation between endoreduplication and fitness compensation. In an effort to establish a direct link between these traits, we used cell-cycle mutant lines to manipulate endoreduplication in plants under herbivory. We report that repressing endoreduplication by knocking out ILP1, and likewise promoting endoreduplication by ILP1 overexpression, directly affects the regrowth and fitness compensation of Columbia plants following herbivory. Our results thus suggest that the endoreduplication pathway and the fitness pathway are directly related, whether via shared genetic pathways or by genetic pathways that influence both processes via some common link.