MaHSFA2c modulates high temperature-inhibited chlorophyll breakdown in banana fruit by directly inducing the transcription of the E3 ligase gene MaBAH1

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Bananas (Musa acuminata, AAA group) ripening at temperatures higher than 24 °C prevent yellow skin development, resulting in green ripening, and significantly affecting the commercial potential of the fruit. Our recent study discovered that high temperature (HT) triggers the E3 ubiquitin ligase MaBAH1 to degrade MaMYB60, thereby suppressing MaMYB60's transactivation of chlorophyll catabolic genes. However, the mechanism by which HT stimulates MaBAH1 expression remains unknown. In this study, a heat shock transcription factor, termed MaHSFA2c, was identified as an upstream regulator of MaBAH1. MaHSFA2c gene expression and protein levels were up-regulated in green-ripened fruit at 30 °C compared to yellow-ripened fruit at 20 °C. MaHSFA2c directly activated the transcription of MaBAH1. Importantly, silencing MaHSFA2c in banana fruit suppressed MaBAH1 expression, reducing MaBAH1-mediated MaMYB60 degradation. This promoted MaMYB60's activation of chlorophyll degradation, thereby weakening green-ripening at HT. In the context of banana fruit, we have demonstrated the existence of a dynamic regulatory module consisting of MaHSFA2c and MaBAH1 that manages chlorophyll catabolism inhibition under HT. These findings enhance our understanding of the transcriptional regulation involved in the loss of fruit quality due to temperature stress and are expected to aid in developing strategies to manage banana green-ripening.

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