A novel role for PRC2 activity in light signalling in Arabidopsis thaliana

Abstract

Light is the major regulator of plant development, controlling a number of key stages throughout the plant life cycle. One of these is the transition from skotomorphogenesis to photomorphogenesis in seedlings upon exposure to light. Perception of light via a suite of photoreceptors initiates a massive reorganisation at the transcriptional, translational and post-translational levels across the seedling. In recent years, increasing evidence has also been presented showing epigenetic changes also play a crucial role in this process. The work in this thesis seeks to contribute to this growing field by identifying that the Polycomb Repressive Complex 2 (PRC2) plays a key role in photomorphogenesis via the deposition of H3K27me3, mediated by the histone methyltransferase CURLYLEAF (CLF).

Phenotypic and genetic analysis shows that CLF activity is upregulated by blue light in a CRY1-dependent manner, and that loss of CLF leads to elongated hypocotyls – a classic phenotypic trait which has been long used to identify deficiencies in light signalling. RNA-seq and ChIP-qPCR analysis indicates that CLF inhibits hypocotyl elongation via the deposition of the silencing chromatin modification H3K27me3 at expansins and XTH genes. It is also shown that CLF further contributes to the enhancement of auxin signalling in cotyledons via the H3K27me3-mediated silencing of AUX/IAA and GH3 genes. Additional phenotypic analysis indicates that CLF also plays a role in other auxin-regulated processes such as phototropism. Finally, a candidate interaction is identified between CLF and the skotomorphogenesis-promoting transcription factor PIF4, indicating an intriguing possible mechanism for CLF regulation during light responses.