Histone Deacetylase Complex 1 and histone 1 epigenetically moderate stress responsiveness of Arabidopsis thaliana seedlings

Summary Early responses of plants to environmental stress factors prevent damage but can delay growth and development in fluctuating conditions. Optimising these trade‐offs requires tunability of plant responsiveness to environmental signals. We have previously reported that Histone Deacetylase Complex 1 (HDC1), which interacts with multiple proteins in histone deacetylation complexes, regulates the stress responsiveness of Arabidopsis seedlings, but the underlying mechanism remained elusive. Here, we show that HDC1 attenuates transcriptome re‐programming in salt‐treated seedlings, and we identify two genes (LEA and MAF5) that inhibit seedling establishment under salt stress downstream of HDC1. HDC1 attenuates their transcriptional induction by salt via a dual mechanism involving H3K9/14 deacetylation and H3K27 trimethylation. The latter, but not the former, was also abolished in a triple knockout mutant of the linker histone H1, which partially mimics the hypersensitivity of the hdc1‐1 mutant to salt stress. Although stress‐induced H3K27me3 accumulation required both H1 and HDC1, it was not fully recovered by complementing hdc1‐1 with a truncated, H1‐binding competent HDC1 suggesting other players or independent inputs. The combined findings reveal a dual brake function of HDC1 via regulating both active and repressive epigenetic marks on stress‐inducible genes. This natural ‘anti‐panic’ device offers a molecular leaver to tune stress responsiveness in plants. See also the Commentary on this article by Archacki, 241: 7–9.