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

<p>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 <i>Rhizophagus irregularis</i> modulates alterations in <i>Medicago truncatula</i> that affect pea aphid’s (<i>Acyrthosiphon pisum</i>) fitness. The results indicate that aphid colony weight increased after feeding on shoots of high <i>R. irregularis</i>-colonized plants relative to non-mycorrhizal controls. Moreover, when given a choice, aphid adults preferred high <i>R. irregularis</i>-colonized plants compared to non-mycorrhizal plants. Interestingly, we identified genes strongly regulated by aphid feeding in shoots (<i>β-1,3 glucanase</i>, <i>thaumatin-like protein</i>, <i>ethylene response factor (ERF) 1</i>, <i>gibberellin (GA) 20-oxidase</i>, and <i>GA 2-oxidase</i>), by AM symbiosis in roots (<i>oxo-phytodienoic acid reductase</i>, <i>ERF1</i>, and <i>GA 20-oxidase</i>), and a gene (<i>GA 2-oxidase</i>) 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.