Unravelling the function of chromatin remodellers in response to environmental stresses

Plants need to perceive a vast range of light qualities to modulate their developmental trajectory accordingly. High red:far red light ratio is a crucial signal that plants perceive through phytochrome B (phyB), important to regulate hypocotyl elongation during photomorphogenesis and to control flowering time. For this reason, many pathways concur with the signalling processes downstream of phytochromes. Epigenetics machineries are highly involved in all biological processes of eukaryotes, playing a fundamental role in plant development and responses, including light responses. HISTONE DEACETYLASE COMPLEX 1 (HDC1) is a scaffold protein that is part of HISTONE DEACETYLASE 6 (HDA6) and HDA19 complexes currently known to regulate abiotic stress responses such as salt stress tolerance. Histone deacetylase complexes are known to interact with other epigenetic machineries, such as Polycomb Repressive Complex 2 (PRC2). PRC2 is the H3K27me3-depositing complex whose catalytic subunit CURLY LEAF (CLF) and SWINGER (SWN) are mainly active in post-embryonic phases. The aim of this project is to investigate the role of HDC1 and PRC2 catalytic subunits CLF and SWN in red light responses. HDC1 has been observed to act during red light-mediated photomorphogenesis by negatively regulating it. Results suggest its role in deacetylating phyB locus and physically protecting from degradation the photomorphogenesis negative regulator PHYTOCHROM INTERACTING FACTOR 4 (PIF4). Furthermore, HDC1 binding to shared photomorphogenesis-related genes seems to be necessary for PIF4 binding and transcriptional activation. CLF and SWN, on the other hand, appear to be both involved in photoperiodic flowering time control, acting in opposite ways upon red light exposure. Altogether, these results suggest a preferential function of HDC1 and PRC2 catalytic subunits under red light, hinting at a possible relationship. Future studies will aim at further elucidating this interaction, employing targeted epigenomic editing techniques to understand the hierarchy between epigenetic marks especially in response to abiotic stimuli.