Epigenetic Regulation of Phase Transitions in Arabidopsis thaliana
Trindade I, Schubert D, Gaudin V – 2017
In plants the adult organs are not determined during embryogenesis. Throughout their life cycle, plants undergo different developmental changes, which require deep alterations in the overall gene expression patterns. The timing at which these phase changes occur can have a strong impact on plant viability and fitness and therefore needs to be tightly regulated to assure they take place under optimal conditions. On the other hand, in Arabidopsis thaliana, once a transition is initiated, it is usually stable, independently of the surrounding environment, suggesting it should be memorized. Over the last years, several studies have shown that epigenetics plays an important role in the regulation of phase transitions in plants. For instance, Arabidopsis mutants where the repressive trimethylation of lysine 27 of histone 3 (H3K27me3) is absent were shown to germinate and further revert into calli-like structures bearing somatic embryos. Moreover, this histone mark has recently been shown to also regulate the transition from vegetative to reproductive development, as some mutants with reduced H3K27me3 levels are incapable of memorizing floral inducible stimuli, when transferred to suboptimal conditions. On the other hand, the epigenetic modifications need to be reset at the end of each generation, to ensure the normal development of the progeny. In fact, plants have developed an entire reprogramming machinery that culminates at gametogenesis, where a genome-wide resetting of gene programs takes place. In this chapter we summarize recent findings on different layers of epigenetic regulation during Arabidopsis major developmental transitions: embryo to seedling, juvenile to adult and vegetative to reproductive. We present phase-specific regulatory mechanisms and highlight common aspects throughout development and the importance of resetting at the end of each generation.