Comparative metabolomics elucidates the early defense response mechanisms to Plutella xylostella infestation in Brassica napus.

Plutella xylostella (diamondback moth; DBM) is a significant pest of Brassica crops, causing billions of dollars in annual global damage and developing resistance to many insecticides. Climate change is increasing the frequency and severity of infestations by influencing the moth's reproduction and expanding its range, leading to increased crop losses. In this study, we examined the early metabolomic responses of four Brassica napus accessions to DBM infestation, focusing on identifying the metabolic basis of tolerance. Phenotypic analysis showed that R4220 and R4415 were highly susceptible, with remaining leaf areas of 27 and 38%, respectively, while the tolerant accessions R4637 and R5064 retained 85 and 91% of their leaf area post-infestation. Metabolomic profiling revealed a distinct separation between tolerant and sensitive accessions under both control and infested conditions. Notably, tolerant accessions exhibited differential accumulation of metabolites, with abundant metabolites belonging to lipid and lipid-like molecules, organic acids and derivatives, and benzenoids. Additionally, 31 metabolites were found to be consistently expressed at higher levels in tolerant accessions as compared to sensitive ones, notably tridecanedioic acid, 3,5-dihydroxyphenylglycine and benzoxazine-6-carboxylic acid. Furthermore, KEGG analysis revealed that pathways such as phenylpropanoid biosynthesis, aminoacyl-tRNA biosynthesis and ABC transporters were enriched, indicating their critical roles in the defense mechanisms. This comprehensive analysis of metabolomic alterations provides valuable insights into the biochemical pathways underpinning insect tolerance in rapeseed, potentially guiding the development of more resilient cultivars and leading a pathway to improve crop farming for sustainable agriculture.