Functional Characterization Of Herbivore Resistance-related Genes OsERF3 And OsACS2 In Rice

Characterizing the mechanisms underlying herbivore-induced plant defense responses has always been one of hotspots in plant moleculer biology. Herbivore attack rapidly activates large-scale and specific transcriptional changes in plants, suggesting important roles of transcription factors in plant-herbivore interaction. Moreover, many studies have confirmed that ethylene signaling is important for manipulating herbivore-induced plant defense responses. Thus, we here chose a rice ERF (ethylene responsive factor) transcription factor gene OsERF3 and an ethylene biosynthesis-related ACS (1-amino-cyclopropane-l-carboxylic acid synthase) gene OsACS2 and characterized their biological functions in regulating herbivore-induced defense responses. The results are as follows:1) OsERF3 localizes nucleus, whose transcripts were rapidly up-regulated in response to mechanical wounding and feeding by the rice striped stem borer (SSB) Chilo suppressalis or rice leaf folder (LF) Cnaphalocrocis medinalis, but slightly suppressed by the rice brown planthopper (BPH) Nilaparvata lugens. Using Agrobacterium tumefaciens-mediated transformation, we generated OsERF3 antisense (as-erf) and over-expression (oe-ERF) transgenic rice plants. OsERF3 positively regulates transcript levels of two mitogen-activated protein kinases (MAPKs) genes, OsMEK3 and OsMPK3, two WRKY genes, OsWRKY53 and OsWRKY70, as well as concentrations of jasmonate (JA), salicylate (SA) and ethylene, and activity of trypsin protease inhibitors (TrypPIs). OsERF3 is also found to mediate rice resistance to SSB. SSB larval weight gain that fed on as-erflines was higher than those fed on WT plants; by contrast, overexpressing OsERF3 decreaced SSB larval growth. Moreover, as-erflines were more severely damaged by SSB than WT plants, whereas oe-ERF lines were less damaged. On the other hand, OsERF3 negatively mediate rice resistance to BPH: as-erf lines decreased feeding and oviposition preference of BPH female adults, and survival rates of BPH nymphae, whereas oe-ERF lines received more BPH female adults, eggs and caused higher survival rates of BPH nymphs. Our results also revealed that OsERF3 regulates rice resistance to SSB and BPH by influencing JA and H2O2 signaling pathways, respectavily. In summary, OsERF3 is an early responsive gene in herbivore-induced defense responses in rice, which can regulate herbivore-induced defense responses and plant resistance by modulating MAPK cascades, and JA, SA, ethylene and H2O2 pathways. Our results also illustrate that OsERF3 acts as a central switch that gears the plant's metabolism towards an appropriate response to chewing or piercing/sucking insects.2) Transcript levels of OsACS2 were rapidly up-regulated in response to mechanical wounding and feeding by SSB, LF or BPH. OsACS2-silenced lines (as-acs) reduced SSB induced ethylene biosnythesis, TrypPI activity and volatile compounds, and decreased rice resistance to SSB. Exogenous application of ACC on as-acs lines can restore elicited TrypPI activity and plant resistance to SSB. By contrast, silencing OsACS2 decreased-the feeding and oviposition preference of BPH female adults, and ACC application can restore the preference. These results suggest that OsACS2 is involved in herbivore induced ethylene biosynthesis, and ethylene signaling plays an important role in rice resistance against chewing- and sucking-herbivores by modulating direct and indirect defenses.