Osa-miR169 Negatively Regulates Rice Immunity against the Blast Fungus Magnaporthe oryzae

Abstract

miR169 is a conserved microRNA (miRNA) family involved in plant development and stress-induced responses. However, how miR169 functions in rice immunity remains unclear. Here, we show that miR169 acts as a negative regulator in rice immunity against the blast fungus <i>Magnaporthe oryzae</i> by repressing the expression of nuclear factor Y-A (NF-YA) genes. The accumulation of miR169 was significantly increased in a susceptible accession but slightly fluctuated in a resistant accession upon <i>M. oryzae</i> infection. Consistently, the transgenic lines overexpressing miR169a became hyper-susceptible to different <i>M. oryzae</i> strains associated with reduced expression of defense-related genes and lack of hydrogen peroxide accumulation at the infection site. Consequently, the expression of its target genes, the NF-YA family members, was down-regulated by the overexpression of miR169a at either transcriptional or translational level. On the contrary, overexpression of a target mimicry that acts as a sponge to trap miR169a led to enhanced resistance to <i>M. oryzae</i>. In addition, three of miR169's target genes were also differentially up-regulated in the resistant accession upon <i>M. oryzae</i> infection. Taken together, our data indicate that miR169 negatively regulates rice immunity against <i>M. oryzae</i> by differentially repressing its target genes and provide the potential to engineer rice blast resistance via a miRNA.