Molecular dissection of rice phytohormone signaling involved in resistance to a piercing-sucking herbivore

Phytohormone, particularly jasmonate (JA) and salicylate (SA) signaling, plays a central role in plant responses to herbivore and pathogen attack. Generally, SA mediates resistance responses against biotrophic pathogens and phloem-feeding insects, while JA mediates responses against necrotrophic pathogens and chewing insects. The phytohormonal responses mediating rice resistance to a piercing-sucking herbivore, the brown planthopper (BPH), remains unknown. Here, we combined transcriptome analysis, hormone measurements, genetic analysis and a field study to address this issue. Infestation by BPH adult females resulted in significant transcriptional reprograming. The upregulated genes were enriched in the JA signaling pathway. Consistently, the concentrations of JAs, but not SA, were dramatically increased in response to BPH attack. Two JA-deficient lines (AOC and MYC2 knockout) and two SA-deficient lines (nahG overexpression and NPR1 knockout) were constructed. BPH performed better on JA-deficient lines than on wild-type (WT) plants, but similarly on SA-deficient and WT plants. During BPH attack, the accumulation of defensive secondary metabolites was attenuated in JA-deficient lines compared with WT plants. Moreover, MYC2 mutants were more susceptible to planthoppers than WT plants in nature. This study reveals that JA signaling functions in rice defense against BPH.

Automated summary

The phytohormone JA plays a crucial role in rice defense against the brown planthopper, while SA does not have a significant impact. Infestation by brown planthopper activates the JA signaling pathway and leads to accumulation of defensive secondary metabolites. JA-deficient lines are more susceptible to brown planthoppers, and MYC2 mutants are more vulnerable to brown planthopper infestation in nature.