CmHY5 and CmWRKY28 regulate sucrose accumulation in oriental melon under supplemental red light

Low light is one of the main environmental factors influencing the content of soluble sugar in oriental melon fruit under protected cultivation. As a supplementary light source, light-emitting diodes have been widely used to improve fruit quality. However, the regulatory mechanism of light quality on oriental melon fruit quality remains unclear. Here, the high sucrose melon fruit was treated with different light qualities during the development stage in a greenhouse, and the results showed that red light significantly increased the sucrose content and upregulated the expression of sucrose transport and metabolism-related genes (CmSUT2, CmSWEET10, and CmSUS2) in melon fruit. In addition, CmWRKY28 was found using a yeast single-hybrid cDNA library, which responded to red light treatment and could bind to the promoters of CmSUT2, CmSWEET10, and CmSUS2 to activate their expression. Moreover, CmHY5 acted as a positive regulator of sucrose accumulation by directly binding to CmSUT2 and CmWRKY28 promoters. CmHY5 also interacted with CmWRKY28 at the protein level to participate in the regulation of sucrose accumulation. Taken together, these findings revealed that red light induced CmHY5 and CmWRKY28 to positively regulate the expression of target genes, promoting the accumulation of more sucrose in melon fruit. This study provided new insights into alleviating the effects of low-light conditions on melon fruit quality.