<i>CmPYL5</i> Mediates Melon Fruit Ripening via Regulation of <i>CmPP2CA6</i> Gene Pathway

Pyrabactin resistance1-like (PYL) receptors are essential for activating abscisic acid (ABA) signalling and play critical roles in plant growth and development. Melon (Cucumis melo) is a horticultural crop cultivated worldwide, yet the molecular functions of CmPYL in melon remain largely unexplored. We performed in situ hybridisation and transcriptomic analysis to investigate the expression patterns of the CmPYL gene in melon. CmPYL5 exhibits specifically high expression levels during the development of melon ovules and fruits. Overexpression of CmPYL5 in melon significantly promotes fruit ripening, advancing 3-5 days compared to WT. Transcriptomic analysis showed that fruit ripening-related genes are significantly altered in the CmPYL5-Oe melon. Silencing of CmPYL5 and overexpression of a Protein Phosphatase-type 2C A6 (CmPP2CA6) gene, which is a negative regulatory component in the ABA signal pathway, both delayed the fruit ripening and affected the accumulation of ethylene, ABA, carotenoids and chlorophyll in melon. Protein interaction assays showed that CmPYL5 and CmPP2CA6 directly interacts in the cell membrane, leading to the inhibition of CmPP2CA6 phosphatase activity. The transcription factors CmABF2 and CmABF4 directly bind to CmPP2CA6 promoter and then activate its transcription. These findings illustrate a novel CmPYL5-CmPP2CA6 gene regulation pathway modulating melon fruit ripening.