Computational identification of MicroRNAs in strawberry expressed sequence tags and validation of their precise sequences by miR-RACE.

MicroRNAs (miRNAs) are small, endogenously expressed, nonprotein-coding RNAs that regulate gene expression at the post-transcriptional level in both animals and plants through repressing translation or inducing mRNA degradation. A comprehensive strategy to identify new miRNA homologs by mining the repository of available strawberry expressed sequence tags (ESTs) was developed. By adopting a range of filtering criteria, we identified 11 potential miRNAs belonging to 5 miRNA families from 47 890 Fragaria vesca EST sequences. Using 2 specific 5' and 3' miRNA RACE PCR reactions and a sequence-directed cloning method, we accurately determined both end sequences of 5 candidate miRNAs. Meanwhile, qRT-PCR was used to detect the expression of these 5 miRNAs in different strawberry organs and tissues at several growing stages. These newly identified F. vesca miRNAs (fve-miRNAs) and their expression information can improve our understanding of possible roles of fve-miRNAs in regulating the growth and development of F. vesca.