Decoding nature's defense dance: Mechanistic insights into biochemical and metabolic shifts in Cajanus cajan and Cajanus platycarpus during combat with the lepidopteran pest Helicoverpa armigera provide evidence for non-host plant immunity

Abstract

This study provides intriguing mechanistic insights into the innate immunity of the pigeonpea wild relative, Cajanus platycarpus, in comparison to the cultivated Cajanus cajan, based on biochemical and metabolic changes during Helicoverpa armigera infestation. Over a 96 h herbivory challenge, both species exhibited 164 metabolites, with 54 undergoing significant alterations. In C. platycarpus, primary carbohydrates such as sucrose, glucose, galactose, and mannose decreased, while structural carbohydrates like xylose, talose, and tagatose accumulated, indicating cell wall damage in C. cajan. Notably, C. platycarpus down-regulated most amino acids except for phenylalanine, which is crucial for the synthesis of defense compounds. The linoleic/linolenic acid pathway, which produces jasmonic acid, was exclusively identified in C. platycarpus, highlighting active defense. As herbivory continued, levels of galactinol, mannitol, and pinitol significantly increased in C. platycarpus, while sorbitol and xylitol levels rose in C. cajan. Essentially, C. platycarpus reduced nutrient availability to insects, enhanced specific defense hormones and pathways, and maintained reactive oxygen species (ROS) equilibrium. These findings offer significant potential for understanding the biology of the wild relative and developing innovative strategies for herbivore control and food sustainability.