Histone deacetylase complex 1 modulates sepal length through the ethylene-ROS module.

HDC1 represses the expression of protein phosphatase genes to promote the activity of key ethylene biosynthetic enzymes, which in turn enhances ROS accumulation during sepal maturation, ultimately influencing sepal length. Organ size is precisely regulated during development to ensure proper function. The sepal must maintain an appropriate size throughout its growth to protect the developing flower bud until blooming. However, the mechanisms regulating sepal size during its maturation remain poorly understood. Here, we identify the histone deacetylase complex 1 (HDC1) as a regulator of sepal size during maturation in Arabidopsis thaliana. Through genetic, transcriptomic, and physiological analyses, we revealed that during sepal maturation, HDC1 repressed the expression of protein phosphatase 2As (PP2As) encoding genes through histone H3 deacetylation, which led to the dephosphorylation and activation of enzymes essential in ethylene biosynthesis. Increased ethylene levels facilitate ROS accumulation to promote sepal maturation and terminate sepal cell elongation, thereby regulating sepal length. Collectively, our study revealed that ethylene and ROS signaling are involved in the HDC1-mediated sepal length regulation during maturation, providing new insights into the molecular mechanisms that govern organ size during development in plants.