Induces the Expression of a MicroRNA to Suppress the Immune Response in Rice.

MicroRNAs play crucial roles in plant responses to pathogen infections. The rice blast disease, caused by the fungus , is the most important disease of rice (). To explore the microRNA species that participate in rice immunity against the rice blast disease, we compared the expression of small RNAs between mock- and -treated rice. We found that infection by strain Guy11 specifically induced the expression of rice miR319 and, consequently, suppressed its target gene (), which encodes a transcription factor. Using transgenic rice that overexpresses miR319b (OE) or expresses -Res (which is resistant to miR319-mediated silencing), we found that is a positive regulator of the rice defense response against the blast disease. When wild-type and miR319b-OE rice were infected by Guy11, multiple jasmonic acid (JA) synthetic and signaling components were suppressed, indicating that Guy11 suppresses JA signaling through inducing miR319. In particular, we found that () and were specifically suppressed by miR319 overexpression or by Guy11 infection. LOXs are the key enzymes of JA synthesis, which catalyze the conversion of α-linoleic acid to hydroperoxy-octadecadienoic acid. The application of α-linoleic acid rescued disease symptoms on the -Res rice but not wild-type rice, supporting our hypothesis that and are the key JA synthesis genes hijacked by Guy11 to subvert host immunity and facilitate pathogenicity. We propose that induced expression of may improve resistance to the rice blast disease.