The Role Of MiR1858a In Rice Resistance Against Bacterial Blight

microRNAs are a class of non-coding～20-25 bp small RNAs, which work as negative regulators for gene expression by cutting the target mRNAs in plants. Actually, microRNAs are not only important for plant growth and development, but also as key regulators in plant responses to multiple stresses. Bacterial blight caused by Xanthomonas oryzae pv. oryzae which belongs to a kind of yellow mutant bacterium is one of the most devastating and widespread bacterial diseases of rice.Based on both gene microarray and proteomic data, five bacterial blight responsive miRNAs including miR1858a were predicted by bioinformatic method. The expression of miR1858a was significantly different between bacterial blight-resistant genotype SH5 and susceptible genotype 8411 when they were inoculated with strain Zhe173. The expression of miR1858a in SH5 was remarkably (p<0.01) induced compared with that in 8411. Meanwhile the expression of miR 1858a in SH5 and 8411 in response to nine Philippines strains, those in four other genotypes in response to Zhe173, and in the seedlings of SH5 that were treated with various abiotic stresses and plant hormones, were also analyzed. The results showed that miR1858a was involved in wide-spectrum resistance to bacterial blight. miR1858a was significantly increased at 2 h and then significantly decreased after 12 h under cold stress, while it significantly decreased within 12 h and then recovered at 24 h under NaCl treatment. The expression of miR1858a was upregulated only at 6 h of drought stress, while it was upregulated after 9 h of methyl viologen treatment. Exogenous salicylic acid could inhibit significantly the expression of miR1858a at three time points in SH5 leaves. The level of miR1858a was significantly increased only at 9 h after jasmonic acid treatment, whereas it was significantly decreased at 6 h and 12 h. miR1858a was significantly upregulated at 6 h, but downregulated at 12 h upon 1-naphthaleneacetic acid treatment.Plant immune can be significantly induced by Harpin proteins, which are main factors to stimulate hypersensive response in plants. HIN1(Harpin-induced 1 domain containing protein) was predicted to be one of the eight target genes of miR1858a by bioinformatic websites and based on the data of gene microarray. The level of HIN1 was significantly (p<0.01) downregulated in SH5 upon Zhe173 attack, which was negatively correlated with miR1858a’s. It was further confirmed that HIN1 was one target gene of miR1858a by RLM-5’RACE. In order to investigate the functions and mechanisms of miR1858a and HIN1 in rice against bacterial blight, some overexpression vectors including OE-pre-miR1858a,OE-HIN1, OE-mutant HIN1 were constructed. And a short tandem target mimic vector called STTM-miR1858a, which was miRNA-resistant, was contrived too. To determine the expression patterns of miR1858a, pre-miR1858a promoter+GUS vector was also constructed. Eventually, the corresponding transgenic seedings were obtained by tissue culture, and the ones will be employed to further work on the biological roles of miR1858a and HIN1.