Histone deacetylation links jasmonic acid signaling to flower size control in rose.

Flower size is a key ornamental trait in roses (Rosa spp.), determined by coordinated regulation of cell proliferation and expansion. Although jasmonic acid (JA) influences plant growth, its role in flower size control remains unclear. Here, we showed that methyl jasmonate (MeJA) treatment reduces flower size in Rosa chinensis, accompanied by elevated expression of the JA-responsive transcription factor RcMYC2. Silencing RcMYC2 resulted in larger flowers due to enhanced petal cell expansion and upregulation of cell expansion-related genes. Mechanistically, RcMYC2 directly bound to the promoter of the expansin gene RcEXPA8 and repressed its transcription via its interaction with the Mediator subunit RcMED25. Consistently, MeJA failed to reduce flower size in RcMED25-silenced plants. Upon JA signal activation, RcMYC2 recruited RcMED25 and the histone deacetylase RcHDA8 to the RcEXPA8 promoter, leading to transcriptional repression via histone deacetylation and restriction of petal cell expansion. These findings demonstrate that histone deacetylation links JA signaling to flower size control, providing new insights into hormone-mediated regulation of organ growth in ornamental plants.