Loss‐of‐Function Mutation in CER 2‐ LIKE 1 Reduced Accumulation of Cuticular Wax and Susceptibility to Thrips in Welsh Onion

ABSTRACT Cuticular waxes can form a hydrophobic barrier on aerial plant surfaces, which is essential for mediating plant‐environment interactions by providing protection against both biotic and abiotic stresses. In this study, a cuticular wax mutant ( gl ) was identified and characterised in Welsh onion ( Allium fistulosum L.), exhibiting a functional deficiency in AfCER2‐LIKE1 . Loss of AfCER2‐LIKE1 function was attributed to a retrotransposon insertion in the promoter region and a frameshift mutation in the coding sequence. In the mutant gl , the loss of function of AfCER2‐LIKE1 (AfCER2‐ LIKE1 gl ) leads to a significant reduction in wax components above C28. Further analysis of yeast heterologous expression showed that AfCER2‐LIKE1 gl is unable to form a complex with AfKCS11 (3‐ketocyl‐CoA, KCS), regulating the elongation of very‐long‐chain fatty acids (VLCFAs) from C28 to C30. Furthermore, the mutant gl showed enhanced resistance to thrips infestation, which served as an observation validated by both field trials and controlled laboratory experiments. Collectively, these findings elucidate the role of CER2‐LIKE1 in regulating VLCFA biosynthesis in Welsh onion and provide insight into the association between cuticular wax and insect resistance. These results offer a theoretical basis for the development of thrips‐resistant germplasm through molecular breeding strategies and suggest potential applications for crop improvement.