Genotypic difference of cadmium tolerance and the associated microRNAs in wild and cultivated barley

Little study was performed to know how microRNAs (miRNAs) are responsive to cadmium (Cd) stress in barley (Hordeum vulgare). In this study, 16 small RNA libraries of shoot and root tissues from a wild barley accession (WB-1) and cultivated barley (Golden Promise) with contrasting Cd tolerance were constructed and sequenced. Moreover, a degradome library was constructed and analyzed to identify target genes of the miRNAs. Based on high-throughput sequencing, 216 conserved miRNAs (in 59 miRNA families) and 87 novel miRNAs were identified. A total of 238 target genes for 149 miRNAs (113 conserved and 36 novel miRNAs) were detected by the degradome analysis. Among these miRNAs, 45 miRNAs (40 conserved and 5 novel miRNAs) and 43 miRNAs (40 conserved and 3 novel miRNAs) showed differential expression in roots and shoots of two genotypes under Cd conditions. Compared with cultivar Golden Promise, the wild genotype WB-1 had genotype-dependent responses of miR156, miR159, miR166, miR167, miR171 and miR393, which regulate target genes including SPL, MYB, HD-Zip, ARF, GRAS and TIR. Correspondingly, WB-1 had lower Cd concentration and stronger Cd tolerance than Golden Promise. It indicates that miRNAs may play critical roles underlying genotypic difference of Cd tolerance in barley.