Sorghum, a rugged, generally salt-tolerant cereal crop, is important for its use as food, forage for animals and as a source for biofuel. However, its salt-tolerance differs greatly among the various genotypes and the mechanism for this variation remains unknown. High salinity in soil is a common stress that leads to desertification of landscapes. The ability to grow sorghum under salt-stress conditions would open previously unusable land to cultivation and is of interest to sorghum breeders, growers, and scientists.
To discover the mechanism by which some varieties of sorghum are salt-tolerant, researchers from the Chinese Academy of Sciences, University of Chinese Academy of Sciences, and Heilongjiang Academy of Agricultural Sciences selected two inbred sorghum lines, RIO and SN005, as representatative of salt-tolerant and intolerant breeds respectively. Under a 100 nM salt treatment there was almost no effect on RIO, while in the SN005 line the germination ratio decreased to 87.8%. Although both lines showed growth inhibition when given a salt treatment (0, 150, 200, and 250 mM) at the three-leaf seedling stage, RIO seedlings were greener and grew better with the added salt than SN005 seedlings. Photosynthesis was also affected with a large reduction in PSII efficiency (ΦPSII) in SN005 plants under the salt treatment compared with RIO plants under these same conditions. These results indicated that the two lines would be good candidates for a comparative study of the mechanisms behind salt-tolerance.
It is known that salt-tolerance in sorghum is controlled by multiple genes and that the response of exposure to salt is dynamic and changes over time. Scientists can get an overall picture of the genes and mechanisms that are part of salt-tolerance through the use of transcriptome analysis. However, past studies have only analyzed the transcriptome level at 1-3 time points, whereas this study uses RNA-seq to evaluate 6 time points, providing a much more comprehensive picture of the process. Through expression pattern cluster analysis, the researchers showed that RIO-specific response genes were significantly enhanced in the secondary metabolic pathways and the hormone signaling pathways categories. In addition, GO enrichment analysis indicated that RIO responded quicker in the first two hours after salt exposure when compared with the SN005. This correlated with the fact that more transcription factors (TFs) in RIO were specifically expressed differently in those same first two hours after treatment; the TF change between the two lines was divergent as well. TFs are of primary importance in the transduction of stress signals to gene expression. They concluded that the early response of the secondary metabolism and hormone signaling was crucial for salt tolerance in sweet sorghum.
References
Chen C, Shang X, Sun M, Tang S, Khan A, Zhang D, Yan H, Jiang Y, Yu F, Wu Y, Xie Q. Comparative Transcriptome Analysis of Two Sweet Sorghum Genotypes with Different Salt Tolerance Abilities to Reveal the Mechanism of Salt Tolerance. Int J Mol Sci. 2022 Feb 18;23(4):2272. PMID: 35216389. DOI: 10.3390/ijms23042272. Read more
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