Comparative metabolomics analysis reveals secondary cell wall thickening as a barrier to resist Aspergillus flavus infection in groundnut

Abstract

AbstractAflatoxin contamination caused by Aspergillus flavus significantly threatens food safety and human health. Resistance to aflatoxin is a highly complex and quantitative trait, but the underlying molecular and biochemical mechanisms are poorly understood. The present study aims to identify the resistance‐related metabolites in groundnut that influence the defense mechanism against aflatoxin. Here, metabolite profiling of resistant (55–437) and susceptible (TMV‐2) groundnut genotypes, which exhibited contrasting levels of resistance to A. flavus growth and aflatoxin accumulation under pathogen‐ or mock‐inoculated treatments, was undertaken using liquid chromatography and high‐resolution mass spectrometry (LC‐HRMS). Non‐targeted metabolomic analysis revealed key resistance‐related metabolites belonging to phenylpropanoids, flavonoids, fatty acids, alkaloids, and terpenoid biosynthetic pathways. The phenylpropanoids ‐ hydroxycinnamic acid amides (HCAAs) and lignins were among the most abundantly accumulated metabolites in the resistant genotype compared to the susceptible genotype. HCAAs and lignins are deposited as polymers and conjugated metabolites to strengthen the secondary cell wall, which acts as a barrier to pathogen entry. Further, histochemical staining confirmed the secondary cell wall thickening due to HCAAs and lignin depositions. Quantitative real‐time PCR studies revealed higher expressions of phenylalanine ammonia‐lyase (PAL), 4‐coumarate: CoA ligase (4CL), cinnamoyl CoA reductase (CCR2), cinnamoyl alcohol dehydrogenase (CAD1), agmatine hydroxycinnamoyl transferase (ACT), chalcone synthase (CHS), dihydroflavonol 4‐reductase (DFR) and flavonol synthase (FLS) in the pathogen‐inoculated resistant genotype than in the susceptible genotype. This study reveals that the resistance to aflatoxin contamination in groundnut genotypes is associated with secondary cell wall thickening due to the deposition of HCAAs and lignins.