Role of jasmonate (JA) and salicylate (SA) pathways in rice defense against herbivore insects

The jasmonate (JA) and salicylate (SA) signaling pathways play a key role in plant defense responses against herbivorous insects in dicotyledon plants. However, their precise defense function in monocotyledon plants, especially in rice (Oryza sativa L.) is largely unknown. We silenced OsCOI1, OsAOS and OsPAL in rice plants via RNA interference (RNAi) to determine the role of JA and SA signaling pathways in rice defense against rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, and brown planthopper (BPH) Nilaparvata lugens, a phloem-feeding insect. In wild-type rice plants (WT), the transcripts of OsCOI1 and OsAOS were strongly and continuously up-regulated by LF infestation and methyl jasmonate (MeJA) treatment, but not by BPH infestation. The content of the trypsin protease inhibitor (TrypPI), the enzymatic activities of polyphenol oxidase (PPO) and peroxidase (POD) were enhanced in response to both LF and BPH infestation, but the activity of lipoxygenase (LOX) was only induced by LF. The RNAi lines with repressed expression of OsCOI1 showed reduced resistance against LF, while OsPAL RNAi lines showed reduced resistance against BPH. Our results suggest that JA pathway is responsive to  chewing insects, while SA pathway is responsive to phloem-feeding insects in rice plants.