Physiological and Transcriptional Analyses Provide Insight Into Maintaining Ion Homeostasis of Sweet Sorghum Under Salt Stress

Abstract

Sweet sorghum is an important bioenergy grass and valuable forage with a strong adaptability to saline environments. However, little is known about the mechanisms of sweet sorghum coping with ion toxicity under salt stresses. Here, we first evaluated the salt tolerance of a sweet sorghum cultivar “Lvjuren” and determined its ion accumulation traits under NaCl treatments; then explored key genes involved in Na+, Cl−, K+ and NO3− transport using transcriptome profiling and qRT-PCR method. The results showed that the growth and photosynthesis of sweet sorghum were unaffected by 50 and 100 mM NaCl treatments, indicative of a strong tolerance of this species to salt stresses. Under NaCl treatments, sweet sorghum could efficiently exclude Na+ from shoots and accumulate Cl− in leaf sheaths to avoid their overaccumulation in leaf blades; meanwhile, it possessed a prominent ability to sustain NO3− homeostasis in leaf blades. Transcriptome profiling identified several differentially expressed genes associated with Na+, Cl−, K+ and NO3− transport in roots, leaf sheaths and leaf blades of sweet sorghum after 200 mM NaCl treatment for 6 and 48 h. Moreover, transcriptome data and qRT-PCR results indicated that HKT1;5, CLCc and NPF7.3-1 should be key genes involved in Na+ retention in roots, Cl− accumulation in leaf sheaths and maintenance of NO3− homeostasis in leaf blades, respectively. Many TFs were also identified after NaCl treatment, which should play important regulatory roles in salt tolerance of sweet sorghum. This work lays a preliminary foundation for clarifying the molecular basis underlying the adaptation of sweet sorghum to adverse environments.