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

Grafting is extensively utilized in melon (<i>Cucumis melo</i> L.) cultivation to improve environmental tolerance and disease resistance. Our previous studies identified <i>CmGH9B3</i>, 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 <i>CmGH9B3</i> 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 <i>CmGH9B3</i>. 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 <i>CmGH9B3</i> 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-<i>CmGH9B3</i> regulatory module, offering practical targets to improve grafting efficiency in melon cultivation.