Isolation And Functional Characterization Of Defense-related Gene OsDR8 In Rice

Although a lot of studies on the defense response were done, processes involved in resistance of plants to incompatible pathogen are still largely uncharacterized. EI35I3, a cDNA clone was identified from different pathogen-host combinations as showing increased expression by cDNA array analysis after pathogen infection. The information suggests that EI35I3 may be involved in disease resistance in a pathogen-nonspecific way.We report here the isolation and functional characterization of the gene Oryza sativa defence-responsive gene 8(OsDR8), represented by the cDNA EI35I3, from the rice cultivar Minghui 63. Silencing of OsDR8 using an RNA interference approach resulted in phenotypic alteration of the plants. The transgenic plants with repressed expression of OsDR8 showed reduced resistance or susceptibility to Xanthomonas oryzae pv. oryzae and Pyricularia grisea causing bacterial blight and blast, which are two of the most devastating diseases in rice worldwide, respectively. The putative product of OsDR8 was highly homologous to an enzyme involved in the biosynthesis of the thiazole precursor of thiamine. Transgenic plants showing repressed expression of OsDR8 and reduced resistance had significantly lower levels of thiamine than the control plants. The expression level of two pathogenesis-related (PR) genes, PRla and PR4, was also decreased in the plants showing repressed expression of OsDR8. These results suggest that the impact of OsDR8 on disease resistance in rice may be through the regulation of PR gene expression. In addition, the accumulation of thiamine may be essential for bacterial blight resistance and blast resistance.