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Zinc finger proteins (ZFPs) are transcription factors involved in multiple cellular functions. We identified a C2H2 type ZFP (MtZPT2-2) in Medicago truncatula and demonstrated that it localizes to the nucleus and inhibits the transcription of 2 genes encoding high-affinity potassium transporters (MtHKT1;1 and MtHKT1;2). MtZPT2-2 transcripts were detected in stem, leaf, flower, seeds and roots, with the highest level in the xylem and phloem of roots and stems. MtZPT2-2 transcription in leaves was reduced after salt stress. Compared with the wild-type (WT), transgenic lines overexpressing MtZPT2-2 had decreased salt tolerance, while MtZPT2-2-knockout mutants showed increased salt tolerance. MtHKT1;1 and MtHKT1;2 transcripts and Na+ accumulation in shoots and roots, as well as in the xylem of all genotypes of plants, were increased after salt treatment, with higher levels of MtHKT1;1 and MtHKT1;2 transcripts and Na+ accumulation in MtZPT2-2-knockout mutants and lower levels in MtZPT2-2-overexpressing lines compared with the WT. K+ levels showed no significant difference among plant genotypes under salt stress. Moreover, MtZPT2-2 was demonstrated to bind with the promoter of MtHKT1;1 and MtHKT1;2 to inhibit their expression. Antioxidant enzyme activities and the gene transcript levels were accordingly upregulated in response to salt, with higher levels in MtZPT2-2-knockout mutants and lower levels in MtZPT2-2-overexpressing lines compared with WT. The results suggest that MtZPT2-2 regulates salt tolerance negatively through downregulating MtHKT1;1 and MtHKT1;2 expression directly to reduce Na+ unloading from the xylem and regulates antioxidant defense indirectly., Competing Interests: Conflict of interest statement. None declared., (© American Society of Plant Biologists 2023. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Common vetch (Vicia sativa L.) is an important annual diploid leguminous forage. In the present study, transcriptomic profiling in common vetch in response to salt stress was conducted using a salt-tolerant line (460) and a salt-sensitive line (429). The common responses in common vetch and the specific responses associated with salt tolerance in 460 were analyzed. Several KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways, including plant hormone and MAPK (mitogen-activated protein kinase) signaling, galactose metabolism, and phenylpropanoid phenylpropane biosynthesis, were enriched in both lines, though some differentially expressed genes (DEGs) showed distinct expression patterns. The roots in 460 showed higher levels of lignin than in 429. α-linolenic acid metabolism, carotenoid biosynthesis, the photosynthesis-antenna pathway, and starch and sucrose metabolism pathways were specifically enriched in salt-tolerant line 460, with higher levels of accumulated soluble sugars in the leaves. In addition, higher transcript levels of genes involved in ion homeostasis and reactive oxygen species (ROS) scavenging were observed in 460 than in 429 in response to salt stress. The transcriptomic analysis in common vetch in response to salt stress provides useful clues for further investigations on salt tolerance mechanism in the future. [ABSTRACT FROM AUTHOR]

Salinity is a major limiting factor that affects crop production. Understanding of the mechanisms of plant salt tolerance is critical for improving crop yield on saline land. Alfalfa (Medicago sativa L.) is the most important forage crop, while its salt tolerance mechanisms are largely unknown. The physiological and transcriptomic responses in two contrasting salt tolerant cultivars to salinity stress were investigated in the present study. "Magnum Salt" showed higher salt tolerance than "Adrenalin," with higher relative germination rate, survival rate, biomass and K+/Na+ ratio after salt treatment. Activities of antioxidant enzymes SOD, CAT and GR, and proline concentrations were upregulated to higher levels in roots and shoots in Magnum Salt than in Adrenalin after salinity stress, except for no difference in GR activity in shoots, and lower levels of O2⋅– and H2O2 were accumulated in leaves. It was interesting to find that salinity caused a decrease in total unsaturated fatty acid in Adrenalin other than Magnum Salt, C18:2 was increased significantly after salinity in Magnum Salt, while it was unaltered in Adrenalin. High quality RNA sequencing (RNA-seq) data was obtained from samples of Magnum Salt and Adrenalin at different time points (0, 2, and 26 h). Generally, "phagosome," "TCA cycle" and "oxidative phosphorylation" pathways were inhibited by salinity stress. Upregulated DEGs in Magnum Salt were specifically enriched in "fatty acid metabolism," "MAPK signaling" and "hormone signal transduction" pathways. The DEGs involved in ionic homeostasis, reactive oxygen species (ROS) scavenging and fatty acid metabolism could partially explain the difference in salt tolerance between two cultivars. It is suggested that salt tolerance in alfalfa is associated with regulation of ionic homeostasis, antioxidative enzymes and fatty acid metabolism at both transcriptional and physiological level. [ABSTRACT FROM AUTHOR]

SUMMARY BILE ACID: SODIUM SYMPORTER FAMILY PROTEIN 2 (BASS2) is localized within chloroplast membranes, facilitating the translocation of pyruvate and Na+ from the cytosol to the plastid, where pyruvate supports isopentenyl diphosphate (IPP) synthesis via the methylerythritol phosphate pathway in C3 plants. Nevertheless, the biological function of BASS2 in C4 plants has not been well defined. This study unveils a previously unidentified role of PvBASS2 in Na+ and pyruvate transport in seashore paspalum (Paspalum vaginatum), a halophytic C4 grass, indicating a specific cellular function within this plant species. Data showed that overexpression of PvBASS2 in seashore paspalum attenuated salt tolerance, whereas its RNAi lines exhibited enhanced salt resistance compared to wild‐type plants, suggesting a negative regulatory role of PvBASS2 in seashore paspalum salt tolerance. The constitutive overexpression of PvBASS2 was also found to reduce salt tolerance in Arabidopsis. Further study revealed that PvBASS2 negatively regulates seashore paspalum salt tolerance, possibly due to elevated Na+/K+ ratio, disrupted chloroplast structure, and reduced photosynthetic efficiency following exposure to salinity. Importantly, our subsequent investigations revealed that modulation of PvBASS2 expression in seashore paspalum influenced carbon dioxide assimilation, intermediary metabolites of the tricarboxylic acid cycle, and enzymatic activities under salinity treatment, which in turn led to alterations in free amino acid concentrations. Thus, this study reveals a role for BASS2 in the C4 plant seashore paspalum and enhances our comprehension of salt stress responses in C4 plants. [ABSTRACT FROM AUTHOR]

The pyrabactin resistance (PYR)/PYR-like (PYL)/regulatory component of ABA receptor (RCAR) proteins are the core components in ABA signaling pathway. A salt and cold induced ABA receptor gene VsPYL5 from common vetch was identified in the present study. Transgenic Arabidopsis overexpressing VsPYL5 had increased ABA sensitivity and higher levels of seed germination rate, survival rate, and the maximal photochemical efficiency of photosystem II (F v /F m) than the wild type (WT) under salinity conditions. Lower levels of the temperature that leads to 50% electrolyte leakage (TEL 50) and higher levels of survival rate after freezing treatment were observed in transgenic lines compared with WT. The results indicated that VsPYL5 regulated salt and cold tolerance positively. Lower levels of Na+ and Na+/K+ ratio but higher levels of K+ and AKT1 , GORK , KAT1 , HKT1 and KUP4 transcripts were observed in transgenic lines compared with WT under salinity conditions. The results indicated that the increased salt tolerance in transgenic lines was associated with the altered Na+ and K+ levels as a result of improved expression of genes involved in Na+ and K+ homeostasis. Antioxidant enzyme activities and their encoding gene transcripts, proline concentration and reactive oxygen species (ROS) levels were increased after treatment with salinity or cold, with lower levels in transgenic lines compared with WT. It is suggested that VsPYL5 -regulated salt and cold tolerance was associated with the increased proline level and antioxidant defense capacity for maintenance of ROS as a result of improved the relevant gene expression under salinity and cold conditions. Overexpression of VsPYL5 led to increased salt and cold tolerance through improved expression of genes involved in Na+ and K+ homeostasis and ROS homeostasis and increased antioxidant defense capacity • Transgenic Arabidopsis overexpressing VsPYL5 had increased ABA sensitivity and enhanced salt and cold tolerance. • Transgenic lines had lower levels of Na+ but higher levels of K+ under salinity conditions. • Maintenance of ROS were associated with cold and salt tolerance in transgenic lines. [ABSTRACT FROM AUTHOR]

Seashore paspalum (Paspalum vaginatum O. Swartz) is an important warm-season turfgrass species with extreme salt tolerance, but investigations on its salt tolerance mechanism are limited. A salt induced PvWAK3 from halophyte seashore paspalum was identified in this study. Overexpression of PvWAK3 in Arabidopsis led to increased salt tolerance. Transgenic plants had higher levels of seed germination rate, root length, number of lateral roots, shoot weight, survival rate, F v / F m , ETR, and NPQ compared with the wild type (WT) under salt stress. Na+ content was increased and K+ content was decreased after salinity treatment, with lower levels of Na+ and Na+/K+ ratio but higher level of K+ in transgenic plants than in WT under salt stress. The improved maintenance of Na+ and K+ homeostasis was associated with the higher transcript levels of K + -Uptake Permease 4 (KUP4), Potassium Transport 2/3 (AKT2), Salt Overly Sensitive 1 (SOS1) and High-Affinity K + Transporter 5 (HAK5) in transgenic plants compared with WT. Superoxide dismutase (SOD), catalase (CAT) and ascorbate-peroxidase (APX) activities, proline concentration, and P5CS1 transcript were increased after salinity treatment, with higher levels in transgenic lines compared with WT, which led to reduced accumulation of O 2 ·− and H 2 O 2 under salt stress. It is suggested that PvWAK3 regulates salt tolerance positively, which is associated with promoted Na+ and K+ homeostasis, activated antioxidant enzymes, and proline biosynthesis under salt stress. • Overexpression of PvWAK3 in Arabidopsis led to increased salt tolerance. • PvWAK3 overexpressing lines had improved Na+ and K+ homeostasis under salt stress. • PvWAK3 overexpressing lines had improved ROS homeostasis. [ABSTRACT FROM AUTHOR]

HAK/KUP/KT transporters play an important role in maintaining K+ and Na+ homeostasis in plants in response to salt stress. A salt induced PvHAK16 from halophyte seashore paspalum (Paspalum vaginatum O. Swartz) was identified in this study. PvHAK16 was localized in the plasma membrane and highly expressed in leaves but not in roots. Overexpression of PvHAK16 in Arabidopsis led to reduced seed germination rate, shoot weight, F v / F m and survival rate but increased ion leakage after salt stress as compared with the wild type. Increased Na+ and decreased K+ levels that led to higher Na+/K+ ratio was observed in transgenic lines after salt stress, which was a result of the net influx of Na+ and net efflux of K+ in transgenic plants. The results suggest that PvHAK16 confers Na+ uptake and K+ efflux under salt stress and thus negatively regulates salt tolerance. Moreover, PvHAK16 expression altered transcript levels of ion homeostasis genes K + -Uptake Permease 7 (KUP7), Potassium Transport 2/3 (AKT2), Salt Overly Sensitive 1 (SOS1) and Gated Outwardly-Rectifying K + Channel (GORK), which were associated with the increased Na+/K+ ratio in transgenic plants. Transgenic plants had reduced transcript levels of stress responsive genes and showed promoted oxidative damage as a result of reduced SOD activity and proline accumulation. • PvHAK16 negatively regulates salt tolerance with increased Na+/K+ ratio. • PvHAK16 confers Na+ uptake and K+ efflux under salt stress. • PvHAK16 expression leads to reduced proline accumulation under salt stress. [ABSTRACT FROM AUTHOR]