关键词: 水稻, 盐胁迫, 转录组, miRNA, tRF

Abstract:

【Objective】 Rice (Oryza sativa L.) is the most important food crop in China. But as a salt sensitive plant, to study the expression pattern of salt stress responding genes in rice has theoretical and practical significance. The dissection of the molecular mechanism and regulatory network in response to salt stress will contribute to salt-tolerant rice breeding. 【Method】 The rice variety Nipponbare seeds were used as experimental materials. Samples were treated with 150 mmol·L ^-1 NaCl for 21 days in 1/2MS medium. Small RNAs were extracted from treated and non-treaded root samples for sequencing. Differentially expressed miRNAs and tRFs (tRNA-derived RNA fragments) were identified using the cut-off of log₂ fold change (log₂FC) >1 or ＜-1, and their predicted target genes were analyzed. The sequencing results and target genes were further verified by real-time quantitative PCRs.【Result】 RPM > 500 for at least one set of data and log₂ FC > 1 or ＜-1 were used as the cut-off threshold, and 31 differently expressed miRNAs were obtained. Among them, the expression of 8 miRNA were up-regulated and 23 miRNA were down-regulated under salt treatment. The differently expressed miRNAs belonged to 12 miRNA families. 8 of these miRNA families have been reported as salt responding ones in Arabidopsis, maize and wheat, including osa-miR397, osa-miR396, osa-miR156, osa-miR167, osa-miR1432, which were down-regulated miRNAs, and osa-miR159, osa-miR168, osa-miR164, which were up-regulated ones under salt treatment, The other 4 miRNA families, namely osa-miR1882, osa-miR1876, osa-miR1423 and osa-miR5077, have not yet been reported in relation to salt stress. 162 target genes of these 31 differentially expressed miRNAs were predicted. Under salt stress, the expression of 34-38nt tRFs were significantly enhanced in rice root, indicating these tRFs were not produced randomly, but induced by salt stress. RPM > 50 and log₂ FC > 1 or ＜-1 were used as the threshold, 3 tRFs were detected as 5' terminal tRFs and 3 tRFs were detected as 3' terminal tRFs. These tRFs are produced from 6 tRNAs. It is suggested that these tRFs function potentially response to salt stress in rice root. 【Conclusion】 In this study, 12 miRNA families responding to salt stress were detected in rice root. Most of their target genes are transcription factors. It is suggested that these miRNAs are involved in the salt response through post-transcriptional regulation of their target genes. In addition, 8 of them were conserved salt responsive miRNAs among plant species. Furthermore, the salt responsive tRFs of rice was examined in transcriptome level. 6 tRFs induced by salt stress were identified.

Key words: Oryza sativa L., salt stress, transcriptome, miRNAs, tRFs