Saline-alkali stress is a widespread adversity that severely affects plant growth and productivity. Saline-alkaline soils are characterized by high salt content and high pH values, which simultaneously cause combined damage from osmotic stress, ionic toxicity, high pH and HCO₃⁻/CO₃²⁻ stress. In recent years, many determinants of salt tolerance have been identified and their regulatory mechanisms are fairly well understood. However, the mechanism by which plants respond to comprehensive saline-alkali stress remains largely unknown. This review summarizes recent advances in the physiological, biochemical and molecular mechanisms of plants tolerance to salinity or salt- alkali stress. Focused on the progress made in elucidating the regulation mechanisms adopted by plants in response to saline-alkali stress and present some new views on the understanding of plants in the face of comprehensive stress. Plants generally promote saline-alkali tolerance by maintaining pH and Na⁺ homeostasis, while the plants responding to HCO₃⁻/CO₃²⁻ stress are not exactly the same as high pH stress. We proposed that pH-tolerant or sensitive plants have evolved distinct mechanisms to adapt to saline-alkaline stress. Finally, we highlight the areas that require further research to reveal the new components of saline-alkali tolerance in plants and present the current and potential application of key determinants in breed improvement and molecular breeding.

Soil salinity is a major environmental factor constraining growth and productivity of highbush blueberry (Vaccinium corymbosum). Leaf Na⁺ content is associated with variation in salt tolerance among blueberry cultivars; however, the determinants and mechanisms conferring leaf Na⁺ exclusion are unknown. Here, we observed that the blueberry cultivar ‘Duke’ was more tolerant than ‘Sweetheart’ and accumulated less Na⁺ in leaves under salt stress conditions. Through transcript profiling, we identified a member of the High-Affinity K⁺ Transporter (HKT) family in blueberry, VcHKT1; 1, as a candidate gene involved in leaf Na⁺ exclusion and salt tolerance. VcHKT1; 1 encodes a Na ⁺ -preferential transporter localized to the plasma membrane and is preferentially expressed in the root stele. Heterologous expression of VcHKT1; 1 in Arabidopsis (Arabidopsis thaliana) rescued the salt hypersensitivity phenotype of the athkt1 mutant. Decreased VcHKT1; 1 transcript levels in blueberry plants expressing antisense-VcHKT1; 1 led to increased Na⁺ concentrations in xylem sap and higher leaf Na⁺ contents compared with wild-type plants, indicating that VcHKT1; 1 promotes leaf Na⁺ exclusion by retrieving Na⁺ from xylem sap. A naturally occurring 8-bp insertion in the promoter increased the transcription level of VcHKT1; 1, thus promoting leaf Na⁺ exclusion and blueberry salt tolerance. Collectively, we provide evidence that VcHKT1; 1 promotes leaf Na⁺ exclusion and propose natural variation in VcHKT1; 1 will be valuable for breeding Na ⁺ -tolerant blueberry cultivars in the future.

Sugar transport from the source leaf to the sink organ is critical for seed development and crop yield, as well as for responding to abiotic stress. SWEETs (sugar will eventually be exported transporters) mediate sugar efflux into the reproductive sink and are therefore considered key candidate proteins for sugar unloading during seed development. However, the specific mechanism underlying the sugar unloading to seeds in Camellia oleifera remains elusive. Here, we identified a SWEET gene named CoSWEET10, which belongs to Clade III and has high expression levels in the seeds of C. oleifera. CoSWEET10 is a plasma membrane-localized protein. The complementation assay of CoSWEET10 in SUSY7/ura3 and EBY.VW4000 yeast strains showed that CoSWEET10 has the ability to transport sucrose, glucose, and fructose. Through the C. oleifera seeds in vitro culture, we found that the expression of CoSWEET10 can be induced by hexose and sucrose, and especially glucose. By generating the restoration lines of CoSWEET10 in Arabidopsis atsweet10, we found that CoSWEET10 restored the seed defect phenotype of the mutant by regulating soluble sugar accumulation and increased plant drought tolerance. Collectively, our study demonstrates that CoSWEET10 plays a dual role in promoting seed development and enhancing plant drought resistance as a sucrose and hexose transporter.

The Agrobacterium tumefaciens-mediated transformation for blueberries remains less efficient than is desirable. A new leaf callus regeneration and genetic transformation system was investigated in blueberries in this study. The leaf explants of cv. ‘Legacy’ and ‘Northland’ were used to establish the stable callus induction system when placed on the woody plant medium (WPM) supplemented with 1.0 mg·L⁻¹ 2, 4-D, 0.4 mg·L⁻¹ 6-BA for 30 d; then, the callus was sub-cultured in the proliferation medium supplemented with 1.5 mg·L⁻¹ 2, 4-D, 0.4 mg·L⁻¹ 6-BA in the darkness at 25 °C every 30 days. The co-cultivation of callus with A. tumefaciens was operated on WPM plus 100 μM acetosyringone for 4 days; then, the transferred callus was grown in WPM supplemented with 1.5 mg·L⁻¹ 2,4-D, 0.4 mg·L⁻¹ 6-BA, 50 mg·L⁻¹ hygromycin, and 200 mg·L⁻¹ cefotaxime. The VcCHS transgenic blueberry callus with both GFP signal and Hyg resistance was obtained from the transformed callus of cv. ‘Northland’. The rate of GFP signal detected in the transformed callus was as high as 49.02%, which was consistent with the PCR assay. Collectively, this study provides a highly efficient genetic transformation system in blueberry callus and a powerful approach for the molecular breeding of blueberries.

The NAC family of transcription factors (TFs) regulate plant development and abiotic stress. However, the specific function and response mechanism of NAC TFs that increase drought resistance in Picea wilsonii remain largely unknown. In this study, we functionally characterized a member of the PwNAC family known as PwNAC31. PwNAC31 is a nuclear-localized protein with transcriptional activation activity and contains an NAC domain that shows extensive homology with ANAC072 in Arabidopsis. The expression level of PwNAC31 is significantly upregulated under drought and ABA treatments. The heterologous expression of PwNAC31 in atnac072 Arabidopsis mutants enhances the seed vigor and germination rates and restores the hypersensitive phenotype of atnac072 under drought stress, accompanied by the up-regulated expression of drought-responsive genes such as DREB2A (DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN 2A) and ERD1 (EARLY RESPONSIVE TO DEHYDRATION STRESS 1). Yeast two-hybrid and bimolecular fluorescence complementation assays confirmed that PwNAC31 interacts with DREB2A and ABF3 (ABSCISIC ACID-RESPONSIVE ELEMENT-BINDING FACTOR 3). Yeast one-hybrid and dual-luciferase assays showed that PwNAC31, together with its interaction protein DREB2A, directly regulated the expression of ERD1 by binding to the DRE element of the ERD1 promoter. Collectively, our study provides evidence that PwNAC31 activates ERD1 by interacting with DREB2A to enhance drought tolerance in transgenic Arabidopsis.

Blueberry is an important horticultural plant that is very susceptible to drought. However, the molecular regulation mechanisms of blueberry tolerance to drought remain elusive. In this study, the transcriptome profile of blueberry by RNA-seq under different degree of drought treatment were conducted and drought-related genes and pathways were screened by using weighted gene co-expression network analysis (WGCNA) and Venn analysis. Interestingly, the leaves and roots of blueberry exhibited different expression patterns under drought treatment and differentially expressed genes (DEGs), GO terms and KEGG pathways showed more enriched in leaves than in roots. The majority of DEGs were associated with signal transduction, transcriptional regulation, and metabolism. 8 key pathways and 8 DEGs were shared both in leaves and roots. Notably, the pathway with the most of core genes in leaves is plant hormone signal transduction, and in roots are MAPK signaling pathway, reactive oxygen species metabolism and the key genes such as VcXTH3, VcPP2C51, and VcPNC1 were identified. For transcription factors, VcABR1, VcABF2, VcMYB108 and VcMYB93 are likely involved in drought response. In metabolism category, VcCYP75A1 was likely involved in anthocyanin biosynthesis, and VcPNC1 in monoterpenoid biosynthesis pathway. The eight DEGs markedly induced under drought exhibited differential expression in leaves and roots. Correspondingly, physiological assays showed that POD activity, ABA content, and anthocyanin biosynthesis in leaves and roots were significantly increased. Collectively, our study revealed the synergistic and distinct defense pathways and mechanisms in leaves and roots of blueberry and explored the potential regulatory network in blueberry response to drought stress.