HISTONE DEACETYLASE COMPLEX 1 modulates sepal length through the ethylene-ROS module

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. Despite its significance, the mechanisms regulating sepal size during its maturation remain poorly understood. Here we identify the HISTONE DEACETYLASE COMPLEX 1 (HDC1) as a positive regulator of sepal size during maturation in Arabidopsis thaliana. hdc1 mutation prolongs sepal elongation due to delayed sepal maturation, thus hindering flowers from opening timely. Transcriptomic and proteomic analyses reveal that both plant hormone ethylene and reactive oxygen species (ROS) signaling are involved in the HDC1s modulation of sepal size during maturation. Further genetic and chemical data show that during sepal maturation, HDC1 upregulates ethylene levels to promote ROS accumulation, thereby regulating the cessation of sepal growth. Collectively, our study revealed that HDC1 integrates ethylene and ROS signaling to regulate sepal maturation, providing new insights into the molecular mechanisms that govern organ size during maturation in plants.