Transcriptional Analysis Of Rice Plants Infested By Rice Stripped Stem Borer Chilo Suppressalis (Walker) And The Functional Characterization Of A Defense-related Gene OsHI-LOX

Characterizing the molecular mechanism of herbivore induced plant defense responses isone of the most important aspects of revealing relationship between insect and plant So far,much has been done in this area in dicotyleon plants such as Arabidopsis, tobacco and tomato.However, little to nothing is known in this aspect in rice, a model monocot species. Therefore,we first analyze the transcriptional response of rice plants 24 h after they were infested by larvaof rice stem stripped borer(SSB), Chilo suppressalis Walker, using Affymetix's 57 K GeneChip(?) Rice Genome Arrays, and then one SSB feeding up-regulated gene OsHI-LOX, whichencoded a rice lipoxygenase was isolated and its role in herbivore-induced rice defenseresponses was investigated. The results are as follows:Transcriptional levels of 4545 genes(about 8% of the total rice genes) in rice were alteredafter plants were infested by SSB larvae, in which the numbers of upregulated anddownregulated genes were 2124 and 2421 respectively. These SSB-regulated genes can beclassified into 18 functional groups, including genes involved in metabolism, energy generation,signal transduction, plant hormones biosynthesis, transcription regulation, stress responses, andso on. Similar to those found in dicotyledon such as Arabidopsis and tobacco, SSB feedingdown-regulated expression levels of most of genes involved in photosynthesis system andelectron transport in photophosphorylation were down-regulated, leading to degradation ofchlorophyll and decreasing the efficiency of photosynthesis, on the other hand, metabolism ofcarbohydrates, such as glycolysis, gluconeogenesis, glyoxylate cycle, TCA were enhancedsignificantly, it is obvious that main energy generation pathway have been changed, ATPsynthesis was generated mainly by photophosphorylation originally, now mainly by oxidativephosphorylation. Lots of genes involved in synthesis and signaling transduction of planthormones such as jasmonic acid(JA), salicylic acid(SA), Ethylene, IAA, ABA, and GA wereregulated by SSB feeding, but as founded in other plants, JA, SA and Ethylene are the mainplant hormones that playing roles in induced defense resistance against SSB. Many intracellularsignaling transduction pathways are involved in SSB activated rice defense resistance, forexamples Ca²⁺ signaling pathway(36 genes were regulated by SSB), G-protein signaling pathway(39 genes), protein phosphatases(21 genes), protein kinases(217 genes), andphosphatidylinositol signal pathway(9 genes). In addition to, expression levels of 289transcription factor genes in 42 transcription factors families were changed, among them 8transcription factor families including AS2, C2C2-Dof, EIL, GRAP-G2-like, GRAS, HSF,MBF1, NAC, PLATZ, SRS, ULT, WRKY, and ZIM, in which 80% genes were up-regulated.Results also provide new information on the interactions between SSB feeding and other stressfactors, many biotic and abiotic stress factors as pathogen attack-, oxygen-, heat-, cold-,nutrition lacking-stress regulated genes are also regulated by SSB feeding. It is indicated thatSSB induced defense resistance in rice was reconstruction process involved in physiology,biochemical, and metabolism, and other areas of rice plants, the process that rice focuses ondefense other than growth and development.In this paper, one of SSB induced genes, OsHI-LOX cDNA(2873 bp) was isolated fromSSB wounded rice stems including ORF sequence(2775 bp), a 5'UTR sequence(14 bp) and a3'UTR sequence(84 bp), and encodes a protein of 924 residues with a predicted molecular weithof 102.82 kDa. OsHI-LOX is a chloroplast located protein, and SSB feeding, wounding and JAtreatment all induce its expression. Antisense inhibition OsHI-LOX expression in rice reduceSSB induced JA and TrypPI synthesis, and decrease rice resistance to two chewing herbivoreSSB(Chilo suppressalis Walker)and RLF(Cnaphalocrocis medinalis Guenee). Treated withJA, antisense transgenic lines could restore the TrypPI activity and resistance to RLF. Incontrast, antisense inhibition OsHI-LOX expression enhance resistance to BPH(Niaparvatalugens St(?)l), resulting in selectivity, Eggs, feeding, nymphae survival ratio of BPH ontransgenic rice plant to declined. The enhanced resistance is related to generating high levels ofH₂O₂ and SA in transgenic lines while infested by BPH, which could cause hypersensitiveresponse(HR) along the infested site. 1"he results indicated that OsHI-LOX was involved inherbivore induced JA biosynthesis, and played the important roles in rice resistance againstchewing-and sucking-herbivore.