Abstract
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.
Highlights
Salt stress is one of the main restrictions to crop production as it affects more than 800 million hectares of land worldwide (Farooq et al, 2017)
All the 4 genes what had shown an elevated expression in sweet sorghum GZ under salt stress and control based on RNA-sequencing, expressed higher than grain sorghum and were induced expressing by salt treatment based on Quantitative real-time PCR (qRT-PCR), and their responses to salt were faster in GZ than in grain sorghum
Swissprot annotation revealed the 4 up-regulated genes fished out above code DFR, Leucoanthocyanidin dioxygenase (LDOX), Anthocyanidin reductase (ANR) and F3H enzymes, which were all involved in the biosynthetic pathway leading to the synthesis of anthocyanins and condensed tannins (Figure 7; Shimada et al, 2005), and the 2 down regulated genes coding POD and cinnamoyl-CoA reductase (CCR) are the key enzymes from phenylalanine to lignin, their down-regulated expressions will help phenylalanine turn to the pathway of synthesis of anthocyanins and condensed tannins
Summary
Salt stress is one of the main restrictions to crop production as it affects more than 800 million hectares (ha) of land worldwide (Farooq et al, 2017). Defense strategies of plants against salinized conditions depend upon activation of cascades of molecular networks involved in stress sensing, signal transduction and the expression of specific stress-related genes and metabolites (Türkan & Demiral 2009; Deinlein et al, 2014; Wang et al, 2010). Understanding the molecular mechanisms of abiotic stress tolerance is critical for developing stress tolerant crop plants and use of saline water in the future. It is relatively more adapted to marginal growing conditions, such as salinity, alkalinity, water stress and other environmental stresses compared with grain sorghum and maize (Zhang et al, 2011; Michael et al, 2017; Regassa & Wortmann 2014). This study, compared sweet and grain sorghum seedlings responses to salt stress based on RNA-sequencing and found genes and pathways in sweet sorghum which may participate in salt stress response by regulation of flavonoid biosynthesis. Our results presented here help us elucidate the salinity stress effects and develop salinity management strategies aimed at enhancing the use of saline water in agriculture based on plant improvements
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