ABSTRACT: Background: MicroRNAs (miRNAs) are a class of single-stranded non-coding small RNAs (sRNAs) that are 20-24 nucleotides (nt) in length. Extensive studies have indicated that miRNAs play important roles in plant growth, development, and stress responses. With more copper (Cu) and copper-containing compounds used as bactericides and fungicides in viticulture, Cu stress has become one of the serious environmental problems that affect plant growth and development. In order to uncover the hidden response mechanisms of Cu stress, many Cu-responsive miRNAs have been detected in several plant species. However, there have been few reports about the grapevine miRNAs in response to Cu. Results: Here, two small RNA libraries were constructed from Cu-treated and water-treated (control) leaves of 'Summer Black' grapevine. Following high-throughput sequencing and filtering, 158 known vvi-miRNAs and 98 novel vvi-miRNAs were identified in the two libraries. Among these, 24 could only be detected in the treatment, and 63 were only detected in the control. Additionally, 100 known vvi-miRNAs were found to be clearly responsive to Cu, among which 96 were down-regulated and four were up-regulated; 47 novel vvi-miRNAs were found to be clearly responsive to Cu, among which 35 were down-regulated and 12 were up-regulated. Subsequently, expression patterns of a set of Cu-responsive vvi-miRNAs were validated by quantitative real-time PCR (qRT-PCR). There existed some consistency in expression levels of Cu-responsive vvi-miRNAs between high-throughput sequencing and qRT-PCR assays. In addition, 92 putative targets for 79 known vvi-miRNAs and 51 putative targets for 22 novel vvi-miRNAs were predicted, and most of the targets are involved in multiple biological processes including transcriptional regulation and response to biotic and abiotic stresses. Conclusions: In this study, 147 Cu-responsive vvi-miRNAs were identified using high-throughput sequencing, and their target genes were predicted, which will be helpful to understanding the molecular mechanisms of miRNAs in response to Cu stress. Furthermore, this work can also provide a foundation for further study of the networks of miRNAs involved in grapevine plant growth and breeding some Cu-tolerant grapevine cultivars. Mixed 'Summer Black' grapevine young leaves (2 weeks old), large leaves (5 weeks old), and old leaves (9 week old) in randomly-selected plants from both the Cu-treated and control groups were collected for high-throughput sequencing. Subsequently, we carried out the analysis of Solexa sequencing data, and performed the research of regulatory modes of grapevine miRNAs on their target genes during Cu stress.
