Arbuscular mycorrhizal symbiosis alters plant gene expression and aphid weight in a tripartite interaction

Mutualistic root associations with arbuscular mycorrhizal (AM) fungi are known to alter interactions with insects aboveground. In this study, we investigated whether root symbiosis with Rhizophagus irregularis modulates alterations in Medicago truncatula that affect pea aphid’s (Acyrthosiphon pisum) fitness. The results indicate that aphid colony weight increased after feeding on shoots of high R. irregularis-colonized plants relative to non-mycorrhizal controls. Moreover, when given a choice, aphid adults preferred high R. irregularis-colonized plants compared to non-mycorrhizal plants. Interestingly, we identified genes strongly regulated by aphid feeding in shoots (β-1,3 glucanase, thaumatin-like protein, ethylene response factor (ERF) 1, gibberellin (GA) 20-oxidase, and GA 2-oxidase), by AM symbiosis in roots (oxo-phytodienoic acid reductase, ERF1, and GA 20-oxidase), and a gene (GA 2-oxidase) exclusively induced in roots during this tripartite interaction. Our data provide novel information about changes in plant gene expression during aphid-plant-AM fungus interactions, and serve as foundation for future transcriptome studies.