High Levels of Phenylpropanoid-Associated Metabolites Are Important Defence Mechanisms of Rice Against Phloem-Feeding...

In rice, some varieties exhibit high resistance to planthoppers. However, the mechanisms underlying this superior resistance remain largely unknown. Here, we found that compared to the variety Yuefeng (YF), brown planthopper (BPH, Nilaparvata lugens) exhibited significantly less feeding and weight gain, slower development, and lower survival rate and fecundity on the variety JN08. JN08 plants had higher phosphorylation levels of constitutive and BPH-induced mitogen-activated protein kinase (MPK) 4 and 6 than YF plants. They also showed quicker and stronger jasmonic acid (JA) and jasmonoyl-isoleucine response to BPH at early stages of infestation as well as higher constitutive and/or BPH-elicited levels of H₂O₂, most tested phenolamides and some tested flavonoids than YF plants. Bioassays showed that four of phenylamides, N-cinnamoylputrescine, N-p-coumaroylagmatine, N-p-coumaroyl-N'-feruloylputrescine and N-feruloyltyramine, all of which had higher levels in JN08 plant than YF plants, had a significant effect on the survival and/or growth of BPH nymphs. Moreover, overexpressing OsPAL1 (phenylalanine ammonia-lyase1), a gene encoding a rate-limiting enzyme in the phenylpropanoid biosynthesis pathway, in rice significantly reduced BPH performance. These results demonstrate that phenylpropanoid-associated metabolites, such as phenylamides and flavonoids, probably regulated by OsMPK4/6-mediated JA and H₂O₂ signalling pathways, play an important role in regulating rice resistance to BPH.