Grafting Modulates Bottle Gourd Flavor via WRKY23- <i>GS1</i> and PHR1- <i>ALMT8</i> Pathways

Grafting in Cucurbitaceae is known to enhance agronomical traits; however, its impact on the underlying fruit flavor quality remains elusive. This study elucidates the biochemical and molecular mechanisms by which pumpkin rootstock alters the content of flavor-related compounds in bottle gourd fruit, conferring Fusarium wilt resistance and increased yield. Sensory-related metabolites were significantly impacted: grafted fruits exhibited increased glutamate content and elevated accumulation of malic and oxalic acids. Mechanistically, grafting induced the LsWRKY23 expression to directly activate LsGS1, a key gene in glutamate biosynthesis. Concurrently, elevated fruit phosphorus levels in grafted plants inhibit LsPHR1 to downregulate the expression of LsALMT8, a malate transporter gene, thereby reducing organic acid exudation. These results delineate a dual regulatory pathway, involving the LsWRKY23-LsGS1 and LsPHR1-LsALMT8 modules through which grafting orchestrates key flavor attributes. This study provides novel insights into rootstock-scion-mediated modulation of fruit flavor chemistry and identifies potential metabolic engineering targets for Cucurbitaceae crop improvement.