Transcriptome of Sorghum Grains at Different Developmental Stages

Starch is the most abundant accumulated substance in the grains of sorghum(Sorghum bicolor L.), the 5th most world-widely cultivated cereal crop, and is widelyused by humans, especially in the direction of brewing in China. However, there arecurrently few reports on the starch biosynthesis regulatory mechanism in sorghumgrains. Here, we employed RNA-seq and ATAC-seq analysis strategies to discover thetranscriptional regulation network responsible for starch biosynthesis in sorghumgrains. Our results profiled all mRNAs in the sorghum grains at nine developmentstages covering the inflorescence, and grains from 3 to 30 days after pollination (DAP).Analysis of the gene sets determined temporal programs of gene expression, includingthousands of transcription factor (TF) genes. We found a close correlation between thesequentially expressed gene sets and distinct cellular and metabolic programs of thedeveloping grains. The cis-elements that bind to multiple TFs were identified via acomparative ATAC-seq assay. Cis-acting elements capable of binding TFs were alsoidentified within the promoter regions of starch biosynthesis related genes (SBRGs).Moreover, the TF of SbNAC68 exhibited predominant expression in developing grainsand demonstrated co-expression patterns with SBRGs. Furthermore, SbNAC68 wasconfirmed to bind to ACGCAA, a typical motif of binding site for the TFs from NACfamily, to affect the promotor activity of SBRGs and regulate gene transcriptions.Collectively, through multiply omics strategies of RNA-seq and ATAC-seq, and thecase dissection of SbNAC68, the present study provides molecular insights oftranscriptional regulations into starch biosynthesis in sorghum grains.