<scp>CmMYBML1</scp> ‐ <scp>CmTGA1</scp> ‐ <scp> <i>CmTPS1</i> </scp> module regulates Chrysanthemum ( <i>Chrysanthemum morifolium</i> ) resistance to the aphid <i>Macrosiphoniella sanbourni</i>

Terpenoids represent one of the most varied groups of secondary metabolites and are essential in numerous biological functions in plants, especially in response to biotic stress. However, the molecular mechanisms underlying the biosynthesis of sesquiterpenes in response to aphid infestation and the impact of sesquiterpenes on aphid feeding behavior remain unclear. Here, we focus on CmTPS1 as a starting point to analyze its catalytic activity in the synthesis of sesquiterpenes. Then, the transcriptional regulatory mechanisms of sesquiterpenes and their role in the defense of chrysanthemum against aphids were explored. After aphid feeding, the methyl jasmonate content in chrysanthemum increased, and the CmMYBML1 expression was upregulated. CmMYBML1 directly binds to the CmTGA1 promoter and activates its expression, and CmTGA1 directly binds to the promoter of the chrysanthemum sesquiterpene synthase gene CmTPS1 and promotes its expression. The cascade regulates the synthesis of various sesquiterpenes, including β-Caryophyllene, β-Copaene, (E)-β-Farnesene, Germacrene D, and Aromadendrene, ultimately enhancing the chrysanthemum's defense against aphids. This study is the first to show that the CmMYBML1-CmTGA1-CmTPS1 module regulates sesquiterpene biosynthesis in response to aphid feeding. Our findings provide new insights into a novel regulatory network by which plants modulate the synthesis of sesquiterpenes to defend against herbivores in chrysanthemum.