The Functional Characterization Of A Rice Linalool Synthase Gene OsLIS And A RLK Gene OsHI-LK1 In Rice Herbivore Resistance

Herbivore induced plant defense response is regulated by complex physiological and biochemical processes, which starts from the recognition of signals from herbivores, followed by activation of signaling pathways, expression of defense-related genes and the production of defense chemicals. Receptor like kinases (RLKs) that may recognize elicitors from herbivore and plant terpenoids, one kind of plant defense chemicals, play important roles in this response. However, which members of RLK are involved in this process and what is the function of terpenoids are little known. Thus, we here cloned a rice gene OsLIS encoding linalool synthase, whose product linalool is one of the most important terpenoids in rice, and a LRR-RLK (Leucine rich repeat receptor like kinase) gene OsHI-LRR-RLK1 (OsHI-LK1), which is up-regulated by SSB (rice stem stripped borer, Chilo suppressalis Walker) infestation and characterized their roles in herbivore induced rice defense responses with combined research methods of reverse genetics, chemical analysis, molecular biology and bioassay.OsLIS is a monoterpene synthase, which is localized in chloroplasts. Tissue specific analysis showed that OsLIS expressed high in rice stems and leaves while low in roots. Expression levels of OsLIS could be significantly enhanced by mechanical wounding, SSB infestation and JA treatment, whereas weakly induced by BPH infestation and not by SA. RNA interference was elected to silence OsLIS to obtain OsLIS silencing (ir-lis) lines. qRT-PCR proved that OsLIS expression levels in ir-lis lines was only about 10% of those in WT (wild type) plants, and the emission of linalool in ir-lis was only 2～5% of that in WT plants. Moreover, silencing OsLIS had no effect on other herbivore-induced plant volatiles. When the various rice genotypes were exposed to the BPH colony, BPH female adults were more often found on ir-lis plants than on WT plants, and eggs were more on ir-lis lines. Compared with ir-lis plants, Anagrus nilaparvatae, which is an egg parasitoid of BPH, preferred the odors from WT plants. The abundance of BPH was found more on ir-lis lines in field experiments whereas parasitism of Anagrus nilaparvatae was higher in WT plants. ir-lis lines also had an influence on the population densities of other herbivores and natural enemies, such as spider, RLF(Cnaphalocrocis medinalis Guenee) and rice aphid.Tissue specific analysis showed that OsHI-LK1 expressed high in rice roots and leaves while low in stems. Transcript levels of OsHI-LK1 were up-regulated by mechanical wounding, JA treatment, and SSB and BPH infestation (1 day after infestation), but not by SA. RNA interference was elected to silence OsHI-LK1 and we finally got silencing OsHI-LK(ir-lk) lines. qRT-PCR analysis showed that OsHI-LK1 expression levels in ir-lk lines were only 15～30% of those in WT rice plants. JA, SA and GLVs levels were lower in ir-lk lines than in WT rice plants after herbivore infestation. Silencing OsHI-LK1 decreased plant resistance to SSB and BPH.