Zhen Wang, Yechun Hong, Yumei Li , Huazhong Shi, Juanjuan Yao, Xue Liu, Fuxing Wang, Sanwen Huang, Guangtao Zhu, Jian-Kang Zhu. 

Plant Biotechnology Journal; 2021 Jan;19(1):20-22. doi: 10.1111/pbi.13443.

Soil salinity is a major constraint on crop cultivability and productivity worldwide (Shabala, 2013). The ion toxicity caused by high salinity is alleviated by the adjustment of cellular Na⁺ and K⁺ homeostasis through the functions of ion transporters such as SOS1 (Salt Overly Sensitive 1) and HKT1 (High‐Affinity Potassium Transporter 1). SOS1 is a plasma membrane Na⁺/H⁺ antiporter mediating Na⁺ extrusion in root epidermal cells to reduce Na⁺ accumulation in plants and in the parenchyma cells of root and shoot xylems to promote Na⁺ translocation from root to shoot, whereas the Na⁺ transporter HKT1 mediates retrieval of Na⁺ from the xylem and may contribute to Na⁺ recirculation from shoot to root (Zhu, 2016). Natural variations in HKT1 have been implicated in salt tolerance in several plant species (An et al., 2017). However, the role of natural variations in SOS1 in adaptation to salt stress has not been reported.

See https://onlinelibrary.wiley.com/doi/10.1111/pbi.13443

Figure 1

The natural variations in SlSOS1 are associated with root Na⁺/K⁺ ratio and salt tolerance in tomato. (a) SlSOS1‐based association mapping and pairwise LD analysis. The variants in the promoter and coding region are highlighted in red and blue, respectively. Each variant is connected to the pairwise LD diagram with a dashed line. Red lines indicate strong LD values of SNP‐659, SNP‐335 and SNP‐334 in the promoter region. (b) Haplotypes of SlSOS1 in the tomato population analysed based on SNP‐334 and SNP‐335. (c) The distribution of SlSOS1 alleles in PIM, CER and BIG groups. The n indicates the number of accessions. (d) A schematic diagram showing the SlSOS1^TS‐21 and SlSOS1^TS‐577 promoter regions. The dots represent nucleotide variations. The nucleotides of SNP‐334 and −335 are indicated in red. The sequence of CRT/DRE motif in the SlSOS1^TS‐21 promoter is underlined. (e) Relative binding affinity of SlDREB2 to the CRT/DRE motifs in SlSOS1 promoter. Reciprocal competitive EMSA to determine the binding of recombinant MBP‐SlDREB2 protein to the promoter region containing the CRT/DRE motifs of SlSOS1^TS‐21 was carried out using the indicated Cy5‐labelled probes and unlabelled competitors. The same region of SlSOS1^TS‐577 promoter was used for analysis. (f, g) SlSOS1 expression in the Hap1 and Hap2 alleles in shoots (f) and roots (g) without or with salt stress treatment. Eleven accessions from each haplotype were used in this experiment. (h) Genomic sequence showing the mutations in SlSOS1 gene generated using CRISPR/Cas9 system in the TS‐21 wild variety. The sgRNA target sites are indicated in blue. The PAM sequence is underlined. (i‐k) Na⁺/K⁺ ratio (i) and the contents of Na⁺ (j) and K⁺ (k) in roots of slsos1‐1, slsos1‐2 and TS‐21 wild‐type plants. Data are shown as means ± SD (n = 4). (l, m) The contents of Na⁺ (l) and K⁺ (m) in the shoots of slsos1‐1, slsos1‐2 and TS‐21 wild‐type plants. Data are shown as means ± SD (n = 4). (n, o) Salt tolerance of slsos1 mutants and wild type (TS‐21) indicated by plant height (n) and growth phenotype (o). Three‐week‐old slsos1‐1, slsos1‐2 and TS‐21 plants were treated with 0, 100 or 150 mM NaCl for 1 week, followed by recovery for 1 week, and then, plant height was measured. Values are means ± SD (n = 6 plants of each genotype). Bars, 5 cm. In the box plots of (b), (f) and (g), boxes indicate the range of the percentiles of the total data using Turkey method, centre values are medians, dashed lines indicate variability outside the upper and lower quartiles, and dots denote outliers. n denotes the number of accessions belonging to each haplotype group. Statistical significance was determined by Student’s t‐test (*P < 0.05, **P < 0.01).