Histone Deacetylase CpHDA3 Is Functionally Associated with CpERF9 in Suppression of CpPME1/2 and CpPG5 Genes during Papaya Fruit Ripening

Histone deacetylase (HDAC) performs important functions in plant growth and development, including fruit ripening. As a complex biological process, fruit ripening involves the histone acetylation modification of ripening-associated genes. Histone deacetylase genes (HDACs) have been well studied in Arabidopsis and rice, but the biological functions of HDACs in papaya are poorly understood. In the present work, three CpHDACs, belonging to the RPD3/HDA1 subfamily, were identified from papaya and named as CpHDA1, CpHDA2, and CpHDA3. CpHDA1 and CpHDA2 were induced by propylene, while CpHDA3 was propylene-repressed. Moreover, CpHDA3 protein could physically interact with CpERF9 and enhance the transcriptional repression activities of CpERF9 to downstream genes CpPME1, CpPME2 and CpPG5. Histone acetylation levels of CpPME1 and CpPG5 were increased during fruit ripening. Taken together, these results suggested that CpERF9 recruits CpHDA3 to form a histone deacetylase repressor complex to mediate pectin methylesterase and polygalacturonase genes expression during papaya fruit ripening and softening.