Paf1c defects challenge the robustness of flower meristem termination in Arabidopsis thaliana

While accumulating evidence suggests that gene regulation is highly stochastic, genetic screens successfully uncovered master developmental regulators, questioning the relationship between transcriptional noise and intrinsic robustness of development. Here we use the Arabidopsis Paf1c mutant vip3, which is impaired in several RNA Pol II-dependent transcriptional processes, to identify developmental modules that are more or less resilient to large-scale genetic perturbations. We find that the control of flower termination is not as robust as classically pictured. In Angiosperms, the floral female organs, called carpels, display determinate growth: their development requires the arrest of stem cell maintenance. In vip3 mutant flowers, carpels displayed a highly variable morphology, with different degrees of indeterminacy defects up to wild-type size inflorescence emerging from carpels. This phenotype was associated with a variable expression of two key regulators of flower termination and stem cell maintenance in flowers, WUSCHEL and AGAMOUS. This phenotype was also highly dependent on growth conditions. Altogether, these results highlight the surprisingly plastic nature of stem cell maintenance in plants, and its Paf1c dependence.