Plants protect themselves from virus infections by several different defense mechanisms. RNA interference (RNAi) is one prominent antiviral mechanism, which requires the participation of AGO (Argonaute) and Dicer/DCL (Dicer-like) proteins. Effector-triggered immunity (ETI) is an antiviral mechanism mediated by resistance (R) genes, most of which encode NBS-LRR family proteins. MicroRNAs (miRNAs) play important regulatory roles in plants, including regulation of host defenses. SMV (Soybean mosaic virus) is the most common virus in soybean and researchers from the University of Inner Mongolia identified dozens of SMV-responsive miRNAs by microarray analysis in a SMV-susceptible soybean line in their recent study.

Among the up-regulated miRNAs, miR168a, miR403a, miR162b and miR1515a predictively regulate expression of AGO1AGO2,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 AGO1DCL1DCL2 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.

LC Sciences

SMV-responsive miRNAs identified by microarray analysis (A) and verified by Northern blot (B) or qRT-PCR experiments (C).

 

Reference
D. Bao, O. Ganbaatar, X. Cui, R. Yu, W. Bao, B. W. Falk, H. Wuriyanghan (2017) Downregulation of genes coding for core RNAi components and disease resistance proteins via corresponding microRNAs might be correlated with successful SMV infection in soybean Mol. Plant Path. doi: 10.1111/mpp.12581 [abstract]

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