Unravelling the function of chromatin remodellers in response to environmental stress

Light is an essential cue for plants, effectively regulating multiple molecular and physiological mechanisms (Li et al., 2021). Phytochrome B (PhyB) is the photoreceptor specialised in perceiving high red:far red-light ratio, which in turn also activates PhyB and allows its translocation to the nucleus (Kim et al., 2023). In the nucleus, upon light, PhyB notably interacts with PHYTOCHROME INTERACTING FACTOR 4 (PIF4), a transcription factor involved in hypocotyl elongation, triggering its degradation and allowing the process known as photomorphogenesis (Pham et al., 2017). Epigenetic marks and chromatin regulation are deeply tied with transcriptional regulation, playing a fundamental role in environmental cues perception. Among those, histone deacetylase complexes formed by catalytic subunits Histone Deacetylase 6 (HDA6) and HDA19 are known to participate to abiotic stress perception and photoperiodic flowering (Ning et al., 2019; Chen et al., 2010). Interestingly, both complexes share a non-catalytic subunit known as HISTONE DEACETYLASE COMPLEX 1 (HDC1), which mimics their deacetylating function in these processes (Perrella et al., 2024). Here, we aim to explore the involvement of HDC1 in photomorphogenesis and its interplay with downstream light signalling components. Our findings suggest that HDC1 is a negative regulator of photomorphogenesis that primarily responds to red light (Fang et al., 2025). HDC1 does not only act through deacetylation, but it also directly interacts with PIF4 and promotes its accumulation. Moreover, ChIP analyses reveal that HDC1-mediated deacetylation is a requisite for PIF4 binding to its targets. ATAC-seq experiments show that HDC1 is not determinant for chromatin accessibility, while loss of PIF4 greatly affects its dynamics. Meta-analysis of publicly available datasets suggest that PIF4-dependent DNA accessibility may be required for the recruitment of the bZIP transcription factor ABRE-binding factor 3 (ABF3), thus revealing a novel interplay between chromatin remodelling and transcription in plants.