Cotton is an important cash crop with a certain salt tolerance, but its germination stage is very susceptible to the damage of salt stress, causing significant yield loss. However, few studies have evaluated the cotton salt tolerance and selected salt tolerance traits at germination stage. Therefore, in this study, 16 cotton samples with geographical representation were randomly selected from 308 cotton germplasms to determine the optimal 200 mmol·L^-1 NaCl in cotton germination experiments. On this basis, the salt tolerance of 308 upland cotton varieties and the growth, ion distribution and transport of highly salt-tolerant and non salt-tolerant cotton germplasms were analyzed. The results showed that the 308 germplasms were classified into five classes through cluster analysis, i.e, (1) highly salt-tolerant germplasms (HST, 49), (2) salt-tolerant germplasms (ST, 169), (3) moderately salt-tolerant class (MST,43), (4) lowly salt-tolerant germplasms (LST, 16), and (5) non-salt-tolerant germplasms (NST, 31). By calculating the salt tolerance index (STI) of various cotton germination and growth parameters and principal component analysis, combined with the correlation analysis and linear regression between mean membership function value (MFV) and STI, the key indexes of cotton germination and growth under salt stress, including total fresh weight, shoot fresh weight, and shoot length, were determined. In addition, three salt tolerance evaluation models constructed with different variables (6 variables in Model 1; 3 variables in Model 2; 1 variable in Model 3) found that the total fresh weight was the most reliable trait for the salt tolerance evaluation. In practical application, the variable selection for modelling could be adjusted based on the experimental workload. The comparison of the K⁺, Na⁺, and Ca²⁺ contents between HST and NST found that the higher the salt tolerance of cotton germplasms, the lower the Na⁺ content in the root system. Besides, the ion ratios and ion selective transport coefficients (ST) was found to be significantly positively correlated with the salt tolerance of cotton. This study will provide a basis for evaluating and breeding salt-tolerant cotton germplasms.

Pathogenesis-related class 10 (PR-10) proteins play a role in plant growth and development, but the underlying molecular mechanisms are unclear. Here, we isolated a salt-induced PR-10 gene from the halophyte Halostachys caspica and named it HcPR10. HcPR10 was constitutively expressed during development and HcPR10 localized to the nucleus and cytoplasm. HcPR10-mediated phenotypes including bolting, earlier flowering, increased branch number and siliques per plant are highly correlated with increased cytokinin levels in transgenic Arabidopsis. Meanwhile, increased levels of cytokinin in plants is temporally correlated with HcPR10 expression patterns. Although the expression of cytokinin biosynthesis genes validated was not upregulated, cytokinin-related genes including chloroplast-related genes, cytokinin metabolism and cytokinin responses genes and flowering-related genes were significantly upregulated in the transgenic Arabidopsis compared to the wild type by transcriptome deep sequencing. Analysis of the crystal structure of HcPR10 revealed a trans-zeatin riboside (a type of cytokinin) located deep in its cavity, with a conserved conformation and protein–ligand interactions, supporting HcRP10 acts as a cytokinin reservoir. Moreover, HcPR10 in Halostachys caspica predominantly accumulated in vascular tissue, the site of long-distance translocation of plant hormones. Collectively, we draw that HcPR10 as a cytokinin reservoir induces cytokinin-related signal transduction in plants, thereby promoting plant growth and development. These findings could provide intriguing insights into the role of HcPR10 proteins in phytohormone regulation in plants and advance our understanding of cytokinin-mediated plant development and could facilitate the breeding of transgenic crops with earlier mature, higher yielding agronomic traits.

Potassium (K+) is a necessary nutrient for plant growth and crop production. The K+ transporter plays crucial roles in the absorption and transport of K+ in plants. Most K+ transporters in Arabidopsis have been reported, but AtKUP12, which is a member of the KT/KUP/HAK family, has not yet been the subject of relevant in-depth research. In the present study, we demonstrated that AtKUP12 plays a crucial role in K+ uptake in Arabidopsis under 100 μM lowK+ and 125 mM salt stress conditions. AtKUP12 transcripts were induced by K+ deficiency and salt stress. We analyzed the K+ uptake of AtKUP12 using the K+ uptake-deficient yeast R5421 and Arabidopsis mutant atkup12. Transformation with AtKUP12 rescued the growth defect of mutant yeast and atkup12 mutant plants at the low-K+ concentration, which suggested that AtKUP12 might be involved in high-affinity K+ uptake in low-K+ environments. In comparison to the wild-type (WT) and atkup12-AtKUP12 complementation lines, atkup12 showed a dramatic reduction in potassium concentration, K+/Na+ ratio, and root and shoot growth on 12-day-old seedlings under the salt conditions; however, there was no significant difference between the complementation and WT lines. Taken together, these results demonstrate that AtKUP12 might participate in salt tolerance in Arabidopsis through K+ uptake and K+/Na+ homeostasis.