Brassinosteroids Mediate Susceptibility to Brown Planthopper by Integrating with Salicylic Acid and Jasmonic Acid Pathways in Rice.

Improved knowledge of the interactions between plants and insects will facilitate better insect control in crops. Brassinosteroids (BRs) play a vital role in plant growth, developmental processes, and responses to pathogen infection, but the role of BRs in interactions between plants and insects remain largely unknown. In this study, we characterized a negative role of BRs in rice defense against brown planthopper (BPH, Nilaparvata lugens) and examined its underlying mechanisms. We found that BPH infestation suppressed the BR pathway while successively activating the salicylic acid (SA) and jasmonic acid (JA) pathways. In addition, BR-overproducing mutants and plants treated with 24-epibrassinolide (BL) showed increased susceptibility to BPH, whereas BR-deficient mutants were more resistant than the wild-type. BRs down-regulated the expression of genes related to the SA pathway and reduced SA content while genes related to the JA pathway were up-regulated and JA content increased after BPH infestation. Furthermore, BR-mediated suppression of the SA pathway was impaired both in JA-deficient and JA-insensitive mutants. Our results demonstrate that BRs promote the susceptibility of rice plants to BPH by modulating the SA and JA pathways.