CmHY5-CmWRKY23/69-CmGH9B3 module mediates red light promoted graft union healing of melon grafted onto squash

Grafting is extensively utilized in melon (Cucumis melo L.) cultivation to improve environmental tolerance and disease resistance. Our previous studies identified CmGH9B3, encoding β-1,4-glucanase, as a key factor promoting cell adhesion during graft union formation in melon scions grafted onto squash rootstocks. However, the upstream regulatory mechanisms controlling CmGH9B3 expression remained unclear. Here, we demonstrate that LED red light significantly enhances graft union healing by activating a transcriptional module involving CmHY5, CmWRKY23, CmWRKY69, and CmGH9B3. Specifically, the light-responsive transcription factor CmHY5 was induced by LED red light and activated the expression of CmWRKY23 and CmWRKY69. These WRKY transcription factors were directly bound to the CmGH9B3 promoter, promoting its expression to accelerate vascular reconnection and graft healing. Our findings establish a mechanistic link between light signaling and graft union formation via the CmHY5-CmWRKY23/69-CmGH9B3 regulatory module, offering practical targets to improve grafting efficiency in melon cultivation.