Mechanisms underlying the response of different resistant quinoa cultivars to Spodoptera exigua feeding

Spodoptera exigua is the main pest that harms quinoa. Its larvae feed on leaves, flowers, and grains, seriously affecting the quality and yield of quinoa. However, faced with the feeding of S. exigua, some quinoa cultivars have the characteristics of avoiding or reducing damage and having compensatory ability after being harmed. This study aims to dissect the defensive responses of quinoa cultivars with differing resistance levels to feeding by S. exigua.

We compared defensive metabolites and transcriptomes among high-resistant (HR), medium-resistant (MR) and highly-susceptible (HS) quinoa genotypes, and verified gene function via heterologous transformation.

The contents of linoleic acid, α-linolenic acid, 12-OPDA, JA and JA-Ile were significantly elevated in MR and HR genotypes. Transgenic Arabidopsis restricted larval feeding, retarded growth and lowered survival of S. exigua. The expression of CqMYC2L1 varied greatly among resistance groups, indicating a potential correlation between JA pathway metabolites. Subcellular localization verified that the CqMYC2L1 protein localizes to the nucleus, and dual-luciferase (LUC/REN) assays confirmed its transcriptional repressive activity. Heterologous overexpression of CqMYC2L1 in Arabidopsis significantly elevated the levels of JA, JA-Ile, 12-OPDA, total alkaloids, phenolic acids and lipids, and CqMYC2L1 (4.15-fold) showed significant induction to varying degrees. Exogenous JA rapidly activated the transcription and protein abundance of CqMYC2L1, consistent with JA accumulation, and Western blot validated the stable expression of CqMYC2L1 protein.

CqMYC2L1 is associated with JA-mediated defensive metabolism, which enhances the accumulation of alkaloids, phenolic acids and lipids to deter S. exigua.