Spatio-temporal expression of miRNAs in tomato tissues upon Cucumber mosaic virus and Tomato aspermy virus infections.

MicroRNAs (miRNAs) play vital roles in regulating plant growth and development. Recent work has shown that miRNA-mediated regulation of cellular mRNA expression is involved in pathogen-host interactions. However, knowledge about the timing and spatial regulation of plant miRNA expression is still limited. Here, we use stem-loop real-time reverse transcription-polymerase chain reaction to quantify the expression changes of seven miRNAs and their target mRNAs in different tomato tissues during the pathogenic processes. Compared with mock-inoculated plants, the expression levels of investigated miRNAs and mRNAs were enhanced by different degrees upon Cucumber mosaic virus (CMV)-Fny and Tomato aspermy virus-Bj infections, but were almost unchanged in CMV-FnyΔ2b (a CMV-Fny 2b-deletion mutant)-infected tomato seedlings. In addition, the obvious up-regulation of several miRNAs and target mRNAs in some tomato tissues suggested their special roles in these tissues' organogenesis and development. Temporal analyses also revealed that the expressions of these miRNAs and mRNAs were highly regulated by different viral infections. Taken together, the observed spatially and temporally changes in miRNAs and target mRNAs expression levels indicate the abilities of different viruses to interfere with miRNA pathway, and are correlated with their respective functions in phenotype determination in different tomato tissues.