Proteomic Profiling of Medicago sativa Leaves upon Spodoptera litura (Lepidoptera: Noctuidae) Invasion: Activation of Defense Pathways and Photosynthetic Resource Reallocation

Abstract

Alfalfa (Medicago sativa L.) is a high-quality perennial leguminous forage that plays vital roles in livestock industry development and ecological restoration. However, Spodoptera litura (Fabricius, 1775) (Lepidoptera: Noctuidae) severely impairs alfalfa yield and quality. At present, systematic proteomic analyses characterizing the expression profiles and regulatory networks of key insect-resistant proteins under herbivory stress remain limited. The objective of this study is to identify the critical anti-insect factors and resolve the regulatory networks controlling alfalfa adaptation to herbivory. In this study, leaf proteomes were compared between plants infested by S. litura for 24 h and non-infested controls. A total of 6427 proteins were identified, including 586 differentially abundant proteins (DAPs). Functional enrichment analyses revealed that these DAPs were significantly enriched in pathways such as phenylpropanoid biosynthesis, flavonoid biosynthesis, α-linolenic acid metabolism and photosynthesis. Herbivory by S. litura increased the abundance of proteins associated with the phenylpropanoid pathway (e.g., PAL, 4CL, and COMT) and core enzymes involved in jasmonic acid (JA) biosynthesis (e.g., LOX2S, AOC, and OPR), whereas multiple photosynthesis-related proteins (e.g., psaB, petE, and ATPF0B) were decreased in abundance. This study elucidates the regulatory network governing insect defense in alfalfa at the proteomic level, providing valuable protein targets and theoretical support for molecular breeding of insect-resistant alfalfa.