Involvement of Arabidopsis histone acetyltransferase HAC family genes in the ethylene signaling pathway.

Epigenetic modifications play a fundamental role in regulating chromatin dynamics and gene expression. The level of histone acetylation is controlled by two functionally antagonistic enzymes, namely histone acetyltransferase (HAT) and histone deacetylase (HDAC). CREB-binding protein (CBP)/p300 proteins, a subfamily of highly conserved HATs, are involved in various physiological events including proliferation, differentiation and apoptosis. In this work, we study the poorly known function of their homologous genes, the HAC genes, in Arabidopsis. We found that hac1-involved mutants displayed pleiotropic phenotypes, in particular hypersensitivity to ethylene both in the dark and in the light. We also found that the transcriptional levels of ethylene-responsive genes are significantly higher in the hac1hac5 double mutant than in wild-type plants. Moreover, an ethylene synthesis inhibitor cannot release the triple responses of hac mutants. These results suggest that HACs are involved in the ethylene signaling pathway.