Rhizobacteria prime the activation of defence and nutritional responses to suppress aphid populations on barley

Interactions between plant and soil microbes are widespread and modulate plant-insect herbivore interactions. Still, it remains unclear how these shapes the overall plant defence responses and the mechanisms involved. Here, we performed bioassays with barley (Hordeum vulgare) plants to study the underlying molecular pathways induced by two rhizobacteria, Acidovorax radicis or Bacillus subtilis, against the phloem feeding aphid Sitobion avenae over three timepoints. Root colonization by A. radicis or B. subtilis suppressed aphid populations on barley. Analysis of differentially expressed genes and co-expressed gene modules revealed a combination of rhizobacteria and aphid induced plant responses. Aphid feeding triggered distinct plant responses in rhizobacteria-inoculated barley compared to controls, in phytohormone, glutathione, and phenylpropanoid pathways within 24 hours. By day 7, stronger responses were observed in phenylpropanoid and nutrient pathways. By day 21, changes occurred in flavonoid pathways and genes related to tissue damage and repair. Our study suggests that rhizobacteria inoculation of barley against aphids is dynamic and acts through several molecular pathways to induce plant resistance (defences) and tolerance (nutrition and growth) to aphids. Future research holds promise for exploiting these interactions for sustainable crop protection and pest management in agriculture.