Ethylene Response Factor MdERFd4 Regulates Programmed Cell Death in Postharvest Apple Fruit Partially by Interacting with Vacuolar Processing Enzyme Gene MdVPEγ2

Abstract

Group VIII ethylene response factors (ERFs) are known to induce programmed cell death (PCD). Vacuolar processing enzyme (VPE) is central to PCD. However, whether and how they interact to regulate PCD remains unknown. We identified MdERFd4, a subgroup VIII-a ERF, which directly binds to the MdVPEγ2 promoter and represses its transcription. Transient overexpression of MdERFd4 or MdVPEγ2 in tobacco leaves and stable overexpression of either in Arabidopsis induced PCD and senescence. Transient overexpression of either gene in apple and tomato fruits promoted PCD and ripening. Compared with apples and tobacco leaves transiently overexpressing MdERFd4 alone, those with simultaneous silencing of MdVPEγ2 displayed attenuated PCD, indicating that MdERFd4 regulates PCD partially via transcriptional modulation of MdVPEγ2. Ethylene negatively regulates MdERFd4 expression but positively regulates MdVPEγ2 expression during apple ripening, suggesting ethylene may modulate PCD via these two genes. Our findings would help decode the molecular mechanism of PCD in postharvest fruits.