Overexpression of microRNA319 impacts leaf morphogenesis and leads to enhanced cold tolerance in rice (Oryza sativa L.).

MicroRNA319 (miR319) family is one of the conserved microRNA (miRNA) families among diverse plant species. It has been reported that miR319 regulates plant development in dicotyledons, but little is known at present about its functions in monocotyledons. In rice (Oryza sativa L.), the MIR319 gene family comprises two members, Osa-MIR319a and Osa-MIR319b. Here, we report an expression pattern analysis and a functional characterization of the two Osa-MIR319 genes in rice. We found that overexpressing Osa-MIR319a and Osa-MIR319b in rice both resulted in wider leaf blades. Leaves of osa-miR319 overexpression transgenic plants showed an increased number of longitudinal small veins, which probably accounted for the increased leaf blade width. In addition, we observed that overexpressing osa-miR319 led to enhanced cold tolerance (4 °C) after chilling acclimation (12 °C) in transgenic rice seedlings. Notably, under both 4 and 12 °C low temperatures, Osa-MIR319a and Osa-MIR319b were down-regulated while the expression of miR319-targeted genes was induced. Furthermore, genetically down-regulating the expression of either of the two miR319-targeted genes, OsPCF5 and OsPCF8, in RNA interference (RNAi) plants also resulted in enhanced cold tolerance after chilling acclimation. Our findings in this study demonstrate that miR319 plays important roles in leaf morphogenesis and cold tolerance in rice.