Osa-miR169 Negatively Regulates Rice Immunity Against The Blast Fungus Magnaporthe Oryzae

Rice blast is one of the most devastating rice diseases threatening world food security.It can cause substantial reduction of output,even no harvests at all.MiRNAs is an important regulatory factor in the process of plant growth and development,which regulates a series of biological processes,including growth,development,and response to various biotic and abiotic stresses.In a previous study,more than 30 miRNAs were identified to be involved in rice immunity against the blast fungus Magnaporthe oryzae by comparing the deep sequencing data of small RNA libraries from the susceptible accession LTH and the resistant accession IRBLkm-Ts.Among these miRNAs,miR169 was selected for the study of this thesis.Based on the identification of resistance to rice blast of transgenic lines,I demonstrated that miR169 acts as a negative regulator in rice immunity against the blast fungus M.oryzae.The main results are described as follows:1.Upon M.oryzae infection,the accumulation of miR169 increased significantly in the susceptible rice varieties LTH,but slightly fluctuated in monogenic resistant accession IRBL9-W.2.The transgenic lines overexpressing miR169a became more susceptible to a variety of M.oryzae strains,and the expression of defense-related genes and the accumulation of hydrogen peroxide at the infection site was significantly inhibited in this transgenic lines.I selected GFP-tagged M.oryzae strain Zhong8-10-14(GZ8)to inoculate rice leaf sheaths,then I found that overexpressing miR169a can facilitate M.oryzae invasion at the early infection stage.3.The expression of miR169' target genes were significantly down-regulated in the transgenic lines overexpressing miR169a,while significantly up-regulated in the miR169a'target mimicry transgenic lines.In addition,I designed a YFP-reporter assey system of miR169a' targets,then transient coexpressing in N.benthamiana with miR169a and miRl 69a' target mimicry,indicating that miR169a can repress its target genes at either post-transcriptional or translational level.4.Overexpressing the target mimic of miR169a make rice more resistant to M.oryzae.5.The expression of miRl 69's target genes were not same in the resistant varieties and susceptible varieties upon M.oryzae infection.These results demonstrated that miR169 negatively regulates rice immunity against M.oryzae by differentially repressing its target genes.