Role Of OsEIL2, A Transcription Factor Of Ethylene Signaling Pathway, In Regulating Rice Disease Resistance

Rice(Oryza sativa) is one of the most commonly grown crops in the world, and more than half of the global population consumes it as a staple food. With the ever-expanding human population, it becomes a serious challenge to keep pace with the increasing global demand for food.Rice blast, caused by Magnaporthe oryzae, rice sheath blight, caused by Rhizoctonia solani and bacteria blight, caused by Xanthomonas oryzae pv. Oryzae(Xoo) are the three most devastating diseases of rice. The annual rice yield losses caused by these diseases range from 10% to 60% in many rice-growing areas, even causing crop failure in some areas. Rice resistance to R. solani is mainly controlled by quantitative trait loci(QTLs). Although resistance(R) genes to M. oryzae and Xoo have been cloned, they are prone to breakdown due to mutations in the pathogen populations. Therefore it becomes urgent to comprehensively understand the mechanism of rice disease resistance and discover new breeding strategies, and then develop long-lasting resistant rice varieties to reduce yield losses.Based on the different modes of nutrition uptaking from the host, pathogens could be divided into three groups: necrotrophs, biotrophs and hemibiotrophs. M.oryzae is a typical hemibiotrophic pathogen, and R. solani is necrotrophic while Xoo is biotrophic. In plant immunity, ethylene is generally thought to act in concert with jasmonic acid to induce resistance to necrotrophs while antagonizing salicylic acid-mediated resistance to biotrophs. Therefore it seems promising to dissect the michanism of rice resistance to different types of pathogens and engineer lasting broad-spectrum resistant varieties by the manupipulation of phytohormones.The massively parallel signature sequencing(MPSS) data shows that the expression of OsEIL2, is significantly induced in rice by the M.oryzae infection. By gene expression experiment, we detectd the induced expression of OsEIL2 at the late stage after inoculation with M. oryzae isolates RO1-1, which is in consistant with the MPSS data. To dertermine its function of disease resistance, we generated OsEIL2 RNAi transgenic lines through agrobacteria-mediated transformation. The inoculations show that the OsEIL2 knockdown lines become more resistant to M.oryzae and Xoo, while more susceptible to R. solani. Next, we generated OsEIL2 overexpression transgenic lines, and obtained its homozygous T-DNA insertion mutant. Genotypic and phenotypic valuations of these lines are in progress.Meanwhile, we have also characterized the function of OsEIL2. Subcellular localization analyses reveal that OsEIL2 is localized in the nucleus of rice protoplasts and tobacco leaves. Yeast one-hybrid assays show that OsEIL2 exhibits strong transcriptional activity. The expression level of OsACO1, encoding a key enzyme in ethylene biosynthesis, is down-regulated in the OsEIL2 RNAi transgenic plants, but the expression of the salicylic acid pathway-related marker genes are not affected. In addition, the ROS production of OsEIL2 RNAi plants is not induced after chitin treatment.Detailed analysis of the OsEIL2 gene will lead to better understanding on the ethylene signaling pathway in rice and the role of ethylene in rice resistance, and also provide new insights to the breeding of long-lasting resistant varieties.