Studys On Several Important Characteristics Of Defense Responses In Rice Induced By The Brown Planthopper Nilaparvata Lugens

When attacked by herbivores,plants can recognize herbivore-associated molecular patterns and then activate defense-related signaling transduction pathways,thereby resulting in the production of specific defense responses.In this process,specific defense-related signaling pathways activated by different herbivores play an important role in defense responses in plants.Therefore,it is important to understand which defense-related signaling pathways were activated by an herbivore.Nilaparvata lugens(rice brown planthopper,BPH)is one of the most important insect pests in rice(Oryza sativa).It has been well documented that BPH infestation can induce rice plants to produce defense responses by altering levels of jasmonic acid(JA),jasmonic acid-isoleucine(JA-Ile),salicylic acid(SA),ethylene and hydrogen peroxide in rice.However,whether BPH infestation also elicits calcium(Ca2+)signaling and which components located at downstream of defense-related signaling pathways were activated by BPH infestation remain largely unknown.In this paper,using rice and BPH as a research system,we explored the relationship between Ca2+ signaling and defense responses in rice induced by BPH,and analyzed the effects of BPH infestation on components located at downstream of defense-related signaling pathways.We also analyzed other characteristics of BPH-induced defense responses in rice.The following results were obtained:Both BPH feeding and oviposition enhanced local cytosolic Ca2+ concentrations,but mechanical wounding could not.The transcript levels of CDPKs and CMLs,two Ca2+ recognizing protein genes,were significantly up-regulated in response to BPH oviposition.Silencing OsMPK3 did not affect cytosolic Ca2+ levels in rice infested by BPH,whereas silencing OsMPK6 decreased cytosolic Ca2+ concentrations in rice infested by BPH feeding or oviposition.The results indicate that both BPH feeding and oviposition can specifically induce Ca2+ signaling in rice,and that isMPK6 has a positive regulatory role on Ca2+ signaling in rice.Transcript levels of genes related to biosynthesis of defense-related signaling molecules like JA?SA and ET and of genes located at downstream of these signaling pathways were significantly up-regulated in response to BPH oviposition.Of these genes,JA responsive genes OsWRKY26,OsJAMyb,OsJAZ8,OsPR10a,ET responsive gene OsPR3 and SA responsive genes OsPR1a,OsWRKY45,OsWRKY62 were significantly induced in early infestation stage.Interestingly,JA typical marker gene OsVSP2 and SA responsive gene OsPR2 were not induced by BPH oviposition,suggesting that these genes did not respond to BPH-induced JA or SA signals.In contrast,BPH feeding only had a slight effect on transcript levels of genes related to these signaling pathways:only OsJAMyb,Os WRKY62,Os WRKY45,OsPR4 and OsPR3 were significantly up-regulated by BPH feeding at 12 h;these genes at other time points and all of other genes at any time were not induced by BPH feeding.These findings suggest that BPH oviposition can specifically activate JA,SA and ET-mediated defense-related signaling pathways in rice,whereas BPH feeding can only weakly induce defense responses in rice.Analyzing the expression of defense-related signal responsive genes revealed that the defense response in rice induced by BPH oviposition is systemic and that the order of infestation by third instar nymphs and gravid female BPH adults influenced the activation of JA and ET signaling pathways in rice.Moreover,OsMPK3/OsMPK6 may negatively regulate BPH oviposition-induced JA and SA signaling pathways in rice.