Genome-Wide Transcriptome Profiling, Characterization, and Functional Identification of NAC Transcription Factors in Sorghum under Salt Stress

Abstract

Salinity stress has become a significant concern to global food security. Revealing the mechanisms that enable plants to survive under salinity has immense significance. Sorghum has increasingly attracted researchers interested in understanding the survival and adaptation strategies to high salinity. However, systematic analysis of the DEGs (differentially expressed genes) and their relative expression has not been reported in sorghum under salt stress. The de novo transcriptomic analysis of sorghum under different salinity levels from 60 to 120 mM NaCl was generated using Illumina HiSeq. Approximately 323.49 million high-quality reads, with an average contig length of 1145 bp, were assembled de novo. On average, 62% of unigenes were functionally annotated to known proteins. These DEGs were mainly involved in several important metabolic processes, such as carbohydrate and lipid metabolism, cell wall biogenesis, photosynthesis, and hormone signaling. SSG 59-3 alleviated the adverse effects of salinity by suppressing oxidative stress (H2O2) and stimulating enzymatic and non-enzymatic antioxidant activities (SOD, APX, CAT, APX, POX, GR, GSH, ASC, proline, and GB), as well as protecting cell membrane integrity (MDA and electrolyte leakage). Significant up-regulation of transcripts encoding the NAC, MYB, and WRYK families, NHX transporters, the aquaporin protein family, photosynthetic genes, antioxidants, and compatible osmolyte proteins were observed. The tolerant line (SSG 59-3) engaged highly efficient machinery in response to elevated salinity, especially during the transport and influx of K+ ions, signal transduction, and osmotic homeostasis. Our data provide insights into the evolution of the NAC TFs gene family and further support the hypothesis that these genes are essential for plant responses to salinity. The findings may provide a molecular foundation for further exploring the potential functions of NAC TFs in developing salt-resistant sorghum lines.

Deciphering Reserve Mobilization, Antioxidant Potential, and Expression Analysis of Starch Synthesis in Sorghum Seedlings under Salt Stress

“…A higher level of ascorbic acid content in tolerant genotypes in the present study is in accordance with the observations of Almeselmani et al [60], who reported higher ascorbic acid content in tolerant wheat genotypes. Compatible solutes, antioxidants, and soluble sugars constitute the biochemical basis of varietal differences associated with salt tolerance [2]. Total soluble carbohydrates act as an osmolyte inside the plant cell, and their accumulation increases the resistance against stress conditions [15].…”

“…This salinity-induced defense mechanism is differential and primarily dependent on differential antioxidant enzymes, salinity extent, and exposure time [68]. SOD is the most effective intracellular enzymatic antioxidant, ubiquitous in all aerobic organisms and all subcellular compartments prone to ROS-mediated oxidative stress [2,10]. Lee et al [69] reported that transgenic tobacco plants overexpressing Cu/Zn-SOD showed tolerance to salt and water stresses.…”

“…Co-expression of H + -PPase together with NHX dramatically enhances the salt tolerance capacity in plants [80]. One of the largest families of plant-specific transcription factors includes NAC regulating several other genes' transcription in response to abiotic stress [2]. Overexpression of SbVPPase in transgenic finger millet enhances the plant's performance under salt stress [81].…”

“…Salinity has become one of the major abiotic stresses that negatively affect plant growth and agricultural production worldwide [1]. According to the Food and Agriculture Organization (FAO), approximately 19.5% of the irrigated land and 2.1% of dry land is saline affected [2]. In addition, in arid and semi-arid regions, the salinization process occurs because of high evaporation and inadequate amounts of precipitation, leading to considerable leaching [3].…”

“…The high concentration of salts in the soil has a destructive effect on the cell membrane's integrity, photosynthetic reactions, activation of several proteases, and absorption of nutrients [13]. Excess salts compromise the physiological and biochemical functions of plants, causing osmotic stress that results in disturbances of water conductance [2]. Tolerant plants use ions as an alternative to organic compounds for osmotic modification, which requires the synthesis of more energy (ATP) [14].…”