Among the up-regulated miRNAs, miR168a, miR403a, miR162b and miR1515a predictively regulate expression of AGO1, AGO2,DCL1 and DCL2 respectively, and miR1507a, miR1507c and miR482a putatively regulate expression of several NBS-LRR family disease resistance genes. Regulation of their target gene expression by these seven miRNAs was validated by both transient expression assays and RLM-RACE experiments. Transcript levels for AGO1, DCL1, DCL2 and five NBS-LRR family genes were repressed at different time points post SMV infection, while the corresponding miRNA levels were upregulated at these same time points. Furthermore, inhibition of miR1507a, miR1507c, miR482a, miR168a and miR1515a by STTM technology compromised SMV infection efficiency in soybean.
These results imply that SMV can counteract soybean defense responses by down-regulation of several RNAi pathway genes and NBS-LRR family resistance genes via inducing the accumulation of their corresponding miRNA levels.