Flavonoid Biosynthesis Pathway Participating in Salt Resistance in a Landrace Sweet Sorghum Revealed by RNA-Sequencing Comparison With Grain Sorghum

Abiotic stresses affect crop productivity worldwide. Plants have developed defense mechanisms against environmental stresses by altering the gene expression pattern which leads to regulation of certain metabolic and defensive pathways. Sorghum [Sorghum bicolor (L.) Moench] is an important crop in those regions irrigated by salty water. Sweet sorghum is a variant of common grain sorghum and is relatively more adapted to marginal growing conditions. Here, we compared the different response to salt stress of sweet and grain sorghum. We investigated six traits related with seed germination under salt-stress and normal conditions, conducted a genome-wide research on the salt effect on the gene expression of a landrace sweet and two grain sorghum by RNA-sequencing at seedling stage. The results showed that salt stress had significant inhibition to sorghum seed germination capability, and the inhibition to grain sorghum was greater. By comparing sweet and grain sorghum and the KEGG pathway analysis based on the DEGs, six genes involved in flavonoid biosynthesis pathway to tannins and anthocyanins from phenylalanine were identified in the landrace sweet sorghum, which expression was significant different with that in grain sorghum. Quantitative real-time PCR (qRT-PCR) data were closely in accordance with the transcript patterns estimated from the RNA-seq data. Tannins accumulation changes were associated with the genes expression under salt stress and control. These suggested that flavonoid biosynthesis pathway was involved in the sorghum resistance to salt stress. The present results suggested that flavonoid biosynthesis plays an important role in the sweet sorghum capacity for salt tolerance.