High-Throughput Sequencing of Small RNAs and Comparative Analysis Between Two Rice Cultivars Different of Cool Temperature Stress Tolerance

In rice (Oryza sativa), cool temperature during reproductive stage causes pollen sterility, which is an agriculturally important phenomenon because it greatly influences on rice yield. Although response to cool temperature stress varies among rice cultivars, key factors of its tolerance and sensitivity are still unclear. Recently, it has been reported that small RNAs and their associated factors such as Argonaute and Dicer-like protein, play important roles in both development and stress response in reproductive organs of rice. Small RNAs, 19 to 25 nucleotide non-coding RNAs, regulate the expression of target genes by post-transcriptional gene silencing (PTGS) or transcriptional gene silencing (TGS). In this study, we acquired and compared expression profiles of small RNAs for anther development between two japonica rice cultivars, Hitomebore (high cool temperature stres tolerance) and Sasanishiki (low cool temperature stress tolerance). Each cultivar was grown under normal, and cool temperature conditions, and anthers were collected at unicellular microspore stage and tricellular pollen stage. Small RNAs were extracted from each samples and sequenced by next generation sequencer. Repeat-associated small RNAs and known microRNAs were identified using BLASTN against repeat sequence database Repbase and small RNA databases miRBase, respectively, and novel microRNAs were predicted from un-annotated sequences. We identified some microRNAs were expressed specifically only in one cultivar, and amount of known and novel microRNAs was different between cultivars in cool temperature growth condition. These results suggest that small RNA could cause a different tolerance against cool temperature stress tolerance in rice anther.