Abstract
Abstract
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.