嫁接是提高西瓜抗性的重要措施，在生产上已经得到广泛应用。愈合是嫁接生物学的核心科学问题，然而，我们对西瓜嫁接愈合的机理还知之甚少。课题组前期研究发现砧木子叶能调控西瓜嫁接愈合，而且和IAA（吲哚-3-乙酸，生长素的主要生物活性成分）相关，但是详细机理不明确。本项目以西瓜自嫁为研究系统，通过砧木子叶切除、外源IAA、IAA运输抑制剂施用、qRT-PCR和RNA原位杂交等手段，重点分析负责IAA运输的PIN基因在砧木子叶叶肉、叶脉和叶柄，砧木和接穗嫁接切口的表达，与砧木和接穗嫁接切口IAA含量、细胞分裂和分化、愈伤组织形成和维管束桥连通相联系，明确砧木子叶IAA调控西瓜嫁接愈合的关键途径，筛选出候选PIN基因。通过CRISPR/Cas9基因编辑和嫁接技术，对候选基因进行功能鉴定，获得关键PIN基因。本项目的完成可为从砧木子叶角度调控西瓜的嫁接愈合提供理论支撑，丰富植物嫁接愈合的基本理论。

Grafting is an important approach to increase watermelon stress tolerance; it is widely applied in practice. Healing is the core scientific question of grafting biology, however, we know little about the mechanism of watermelon grafting healing. Previously, our group found that the rootstock cotyledon can regulate the grafting healing of watermelon, and it is related to IAA (Indole-3-acetic acid, the major biologically active form of auxin), however, the detailed mechanism remains unclear. In this project, the self-grafted watermelon will be used as the experiment system, by using the techniques such as rootstock cotyledon excision, application of exogenous IAA, IAA transport inhibitors, qRT-PCR and RNA in situ hybrization, the expression of PIN genes in the rootstock cotyledon mesophyll, vein and petiole, as well as grafting cut of rootstock and scion will be investigated, and linked with the IAA content, cell division and differentiation, callus formation, and vascular bundle connection in the grafting cut of rootstock and scion, the key IAA pathway and candidate PIN genes of rootstock cotyledon mediating watermelon grafting healing will be identified. Further, by using CRISPR/Cas9 gene editing and grafting techniques, the function of candidate PIN genes will be identified, and the key PIN genes will be confirmed. The implementation of this project can provide the theoretical basis for the regulation of watermelon grafting healing from the rootstock cotyledon aspect, and can enrich the basic theory of plant grafting healing biology.