Discovering of the transcriptional regulatory network involved in starch biosynthesis in sorghum grains

Starch is the most abundant accumulated substance in the grains of sorghum (Sorghum bicolor), the 5th most world-widely cultivated cereal crop, and is widely used by humans, especially in the direction of brewing in China. However, there are currently few reports on the starch biosynthesis regulatory mechanism in sorghum grains. Here, we employed RNA-seq and ATAC-seq strategies to discover the transcriptional regulation network responsible for starch biosynthesis in sorghum grains. Our results profiled all mRNAs in the sorghum grains at nine development stages covering the inflorescence, and grains from 3 to 30 days after pollination (DAP). Analysis of the gene sets determined temporal programs of gene expression, including thousands of transcription factor (TF) genes. We found a close correlation between the sequentially expressed gene sets and distinct cellular and metabolic programs of the developing grains. The cis-elements serving as binding sites of multiple TFs were identified via a comparative ATAC-seq assay. Cis-elements capable of binding TFs were also identified within the promoter regions of starch biosynthesis related genes (SBRGs). Moreover, the NAC family TF of SbNAC68 highly expressed in developing grains and demonstrated co-expression patterns with SBRGs. Furthermore, SbNAC68 was confirmed to bind to 5'-ACGCAA-3', a typical motif of binding site for the TFs from NAC family, to affect the promotor activities of SBRGs and regulate their transcriptions. Collectively, through multiply omics strategies and the case dissection of SbNAC68, the present study provides molecular insights of transcriptional regulations into starch biosynthesis in sorghum grains.