Genome-wide identification of cucumber green mottle mosaic virus-responsive microRNAs in watermelon.

Cucumber green mottle mosaic virus (CGMMV) is a damaging pathogen that attacks crop plants belonging to the family Cucurbitaceae. Little is known about the regulatory role of microRNAs (miRNAs) in response to CGMMV infection. To identify CGMMV-responsive miRNAs, two sRNA libraries from mock-inoculated and CGMMV-infected watermelon leaves were constructed and sequenced using Solexa sequencing technology. In total, 471 previously known and 1,809 novel miRNAs were obtained, of which 377 known and 246 novel miRNAs were found to be differentially expressed during CGMMV infection. The target genes for the CGMMV-responsive known miRNAs are active in diverse biological processes, including cell wall modulation, plant hormone signaling, defense-related protein induction, primary and secondary metabolism, regulation of virus replication, and intracellular transport. The expression patterns of some CGMMV-responsive miRNAs and their corresponding targets were confirmed by RT-qPCR. One target gene for miR156a-5p was verified by 5'-RNA-ligase-mediated rapid amplification of cDNA ends (5'-RLM-RACE) analysis. The results of this study provide further insights into the miRNA-mediated regulatory network involved in the response to viral infection in watermelon and other cucurbit crops.