Differential expression of micro RNA s and other small RNA s in barley between water and drought conditions

Summary Drought is a major constraint to crop production, and micro RNA s (mi RNA s) play an important role in plant drought tolerance. Analysis of mi RNA s and other classes of small RNA s (s RNA s) in barley grown under water and drought conditions reveals that drought selectively regulates expression of mi RNA s and other classes of s RNA s. Low‐expressed mi RNA s and all repeat‐associated si RNA s (rasi RNA s) tended towards down‐regulation, while t RNA ‐derived s RNA s (ts RNA s) had the tendency to be up‐regulated, under drought. Antisense s RNA s (putative si RNA s) did not have such a tendency under drought. In drought‐tolerant transgenic barley overexpressing DREB transcription factor, most of the low‐expressed mi RNA s were also down‐regulated. In contrast, ts RNA s, rasi RNA s and other classes of s RNA s were not consistently expressed between the drought‐treated and transgenic plants. The differential expression of mi RNA s and si RNA s was further confirmed by N orthern hybridization and quantitative real‐time PCR (q RT ‐ PCR ). Targets of the drought‐regulated mi RNA s and si RNA s were predicted, identified by degradome libraries and confirmed by q RT ‐ PCR . Their functions are diverse, but most are involved in transcriptional regulation. Our data provide insight into the expression profiles of mi RNA s and other s RNA s, and their relationship under drought, thereby helping understand how mi RNA s and s RNA s respond to drought stress in cereal crops.