Additive and epistatic interactions between AKR and AIN loci conferring bluegreen aphid resistance and hypersensitivity in Medicago truncatula

Aphids, including the bluegreen aphid (BGA; Acyrthosiphon kondoi), are important pests in agriculture. Two BGA resistance genes have been identified in the model legume Medicago truncatula, namely AKR (Acyrthosiphon kondoi resistance) and AIN (Acyrthosiphon induced necrosis). In this study, progeny derived from a cross between a resistant accession named Jester and a highly susceptible accession named A20 were used to study the interaction between the AKR and AIN loci with respect to BGA performance and plant response to BGA infestation. These studies demonstrated that AKR and AIN have additive effects on the BGA resistance phenotype. However, AKR exerts dominant suppression epistasis on AIN-controlled macroscopic necrotic lesions. Nevertheless, both AKR and AIN condition production of H₂O₂ at the BGA feeding site. Electrical penetration graph analysis demonstrated that AKR prevents phloem sap ingestion, irrespective of the presence of AIN. Similarly, the jasmonic acid defense signaling pathway is recruited by AKR, irrespective of AIN. This research identifies an enhancement of aphid resistance through gene stacking, and insights into the interaction of distinct resistance genes against insect pests.