Identification of differentially expressed microRNA in the stems and leaves during sugar accumulation in sweet sorghum.

MicroRNAs (miRNAs) have been shown to play important roles in plant development, growth and stress response. Sweet sorghum [Sorghum bicolor (L.) Moench] is an important source of bioenergy due to the high sugar content in its stems. However, it is not clear how the miRNA is involved in sugar accumulation in sorghum stems. In order to identify the miRNAs in the stems and the leaves of sweet sorghum, we extracted RNAs of the stems and leaves of sweet sorghum (Rio) and grain sorghum (BTx623) at the heading and dough stages for high-throughput sequencing. A total of 179279048 reads were obtained from Illumina-based sequencing. Further analysis identified nine known miRNAs and twelve novel miRNAs that showed significantly and specifically differentially expressed in the stems of sweet sorghum. The target genes of the differentially expressed novel miRNAs include the transcription factor, glucosyltransferase, protein kinase, cytochrome P450, transporters etc. GO enrichment analysis showed that the predicted targets of these differentially expressed miRNAs participated in diverse physiological and metabolic processes. We performed RT-qRCR analysis on these miRNAs across eight different libraries to validate the miRNAs. Finally, we screened stem-specifically expressed novel miRNA and a leaf-specifically expressed novel miRNA in sweet sorghum comparing with grain sorghum. Our results provide a basis for further investigation of the potential role of these individual miRNAs in sugar accumulation.