| description |
The wild strawberry Fragaria vesca has recently emerged as an excellent model for investigating flower and fruit traits in economically important fruit crops. Its history of physiological studies combined with sequenced genome and full complements of molecular genetic tools facilitate investigations into mechanisms of its unique biological processes such as fleshy fruit development from the enlarged stem tip called receptacle. Sequencing of nine small RNA libraries encompassing vegetative, flower, and fruit tissues led to the identification of 22 conserved and 10 less-conserved miRNAs as well as 41 novel miRNAs that are likely specific to the strawberry. High throughput Parallel Analyses of RNA ends (PARE) were performed to identify miRNA-guided cleavage events and corresponding target genes. We found that most conserved miRNAs developed species-specific target genes in addition to conserved targets, highlighting the dynamic and fluid nature of the miRNA_target relations. Significantly, we discovered two novel clusters of miRNAs, which together target up to 94 F-box genes. Within one of the clusters is a 22 nt novel miRNA, miRN39, that was expressed preferentially in the developing receptacle fruit and triggered phased siRNA production from six primary FBX PHAS loci. This miRN39-phasiFBX pathway may be involved in regulating disease resistance in the receptacle fruit. In addition, a modified “two-hit” mode of tasiRNA processing was identified in F. vesca, suggesting flexibility in applying previously set rules. A major theme that emerges from this work is that novel miRNAs and miRNA-phasiRNA networks may have evolved to regulate recently expanded gene families so as to control species-specific biological or physiological processes.Overall design: 8 sRNA libraries and 3 PARE (degradome) libraries without replicates |