Altered accumulation of osa-miR171b contributes to rice stripe virus infection by regulating disease symptoms.

Viral infection affects the pattern of plant miRNA expression. It has been presumed that reduction of miR171 and several other miRNAs influences viral symptoms in plants. We here experimentally demonstrate the association of osa-miR171b with rice stripe virus (RSV) symptoms in rice. Inhibition of osa-miR171b caused stunting with reduced chlorophyll content in leaves similar to viral symptoms. Overexpression of osa-miR171b by an artificial miRNA extended vegetative growth and enhanced chlorophyll accumulation in leaves. Tillers were thicker, and panicles were longer with more spikelets in plants overexpressing osa-miR171b than in controls, but there were no differences in tiller numbers. Targets of osa-miR171b, OsSCL6-IIa, OsSCL6-IIb, and OsSCL6-IIc, were respectively up- and down-regulated in plants where osa-miR171b was inhibited or overexpressed. In plants overexpressing osa-miR171b, five positive regulators for heading development, Ehd1, Ehd2, Ehd3, Ehd4, and Hd3a were up-regulated, while the negative regulator Ghd7 was down-regulated. Plants overexpressing osa-miR171b were less susceptible to RSV and virus symptoms were attenuated. Taken together, the results reveal that a reduction of osa-miR171b in RSV-infected rice contributes to RSV symptoms, and provide more insight into the roles of osa-miR171b in rice.