Abstract

Calmodulin-like protein (CML) is one of calcium sensor proteins that are responsible for receiving, translating and transmitting calcium signaling to downstream targets. In this research, it was observed that CpCML46 exhibits an expression profile strongly associated with papaya fruit ripening. The transient overexpression and virus-induced gene silencing (VIGS) assays demonstrated that CpCML46 acts as a positive player in enhancing papaya fruit ripening. The heterologous overexpression of CpCML46 in tomato also promotes the ripening of fruits and promotes the transcription of ripening-associated genes. CpCML46 interacts with the transcription factor CpERF12, which acts as a transcriptional suppressor, with its expression level progressively declining during fruit ripening. Ethephon (ETH) treatment inhibits its expression while 1-methylcyclopropene (1-MCP) treatment promotes it. CpERF12 binds to and inhibits the promoter activities of the ethylene signal transduction-related gene CpETR2-like , and the cell wall degradation and remodeling-related genes CpPE , CpPE12 and CpEXPA11 . The interaction of CpCML46 and CpERF12 reduced the inhibitory effect of CpERF12 on downstream target genes. Transient overexpression of CpERF12 inhibited the ripening process of papaya fruits, repressed the expression of CpETR2-like , CpPE , CpPE12 and CpEXPA11 . The present work reveals that CpCML46 not function as canonical calcium sensor, but interact with CpERF12 to form a CpCML46-CpERF12 regulator module, involved in the ethylene signal to mediate papaya fruit ripening.