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Mycorrhizal associations are known to improve the hydro-mineral nutrition of their host plants. However, the importance of mycorrhizal symbiosis for plant potassium nutrition has so far been poorly studied. We therefore investigated the impact of the ectomycorrhizal fungus Hebeloma cylindrosporum on the potassium nutrition of Pinus pinaster and examined the involvement of the fungal potassium transporter HcTrk1. HcTrk1 transcripts and proteins were localized in ectomycorrhizas using in situ hybridization and EGFP translational fusion constructs. Importantly, an overexpression strategy was performed on a H. cylindrosporum endogenous gene in order to dissect the role of this transporter. The potassium nutrition of mycorrhizal pine plants was significantly improved under potassium-limiting conditions. Fungal strains overexpressing HcTrk1 reduced the translocation of potassium and phosphorus from the roots to the shoots of inoculated plants in mycorrhizal experiments. Furthermore, expression of HcTrk1 and the phosphate transporter HcPT1.1 were reciprocally linked to the external inorganic phosphate and potassium availability. The development of these approaches provides a deeper insight into the role of ectomycorrhizal symbiosis on host plant K(+) nutrition and in particular, the K(+) transporter HcTrk1. The work augments our knowledge of the link between potassium and phosphorus nutrition via the mycorrhizal pathway.

The high-affinity potassium transporter (HKT) genes are essential for plant salt stress tolerance. However, there were limited studies on HKTs in maize ( ), and it is basically unknown whether natural sequence variations in these genes are associated with the phenotypic variability of salt tolerance. Here, the characterization of was reported. Under salt stress, expression increased strongly in salt-tolerant inbred lines, which accompanied a better-balanced Na /K ratio and preferable plant growth. The association between sequence variations in and salt tolerance was evaluated in a diverse population comprising 54 maize varieties from different maize production regions of China. Two SNPs (A134G and A511G) in the coding region of were significantly associated with different salt tolerance levels in maize varieties. In addition, the favorable allele of identified in salt tolerant maize varieties effectively endowed plant salt tolerance. Transgenic tobacco plants of overexpressing the favorable allele displayed enhanced tolerance to salt stress better than overexpressing the wild type . Our research showed that expression could effectively enhance salt tolerance by maintaining an optimal Na /K balance and increasing the antioxidant activity that keeps reactive oxygen species (ROS) at a low accumulation level. Especially, the two SNPs in might be related with new amino acid residues to confer salt tolerance in maize. Two SNPs of related with salt tolerance were identified by association analysis. Overexpressing in tobaccos showed that the SNPs might enhance its ability to regulating Na /K homeostasis.

Background High-affinity potassium transporters (HKTs) are crucial in facilitating potassium uptake by plants. Many types of HKTs confer salt tolerance to plants through regulating K + and Na + homeostasis under salinity stress. However, their specific functions in cassava ( Manihot esculenta ) remain unclear. Results Herein, an HKT gene ( MeHKT1 ) was cloned from cassava, and its expression is triggered by exposure to salt stress. The expression of a plasma membrane-bound protein functions as transporter to rescue a low potassium (K + ) sensitivity of yeast mutant strain, but the complementation of MeHKT1 is inhibited by NaCl treatment. Under low K + stress, transgenic Arabidopsis with MeHKT1 exhibits improved growth due to increasing shoot K + content. In contrast, transgenic Arabidopsis accumulates more Na + under salt stress than wild-type (WT) plants. Nevertheless, the differences in K + content between transgenic and WT plants are not significant. Additionally, Arabidopsis expressing MeHKT1 displayed a stronger salt-sensitive phenotype. Conclusion These results suggest that under low K + condition, MeHKT1 functions as a potassium transporter. In contrast, MeHKT1 mainly transports Na + into cells under salt stress condition and negatively regulates the response of transgenic Arabidopsis to salt stress. Our results provide a reference for further research on the function of MeHKT1 , and provide a basis for further application of MeHKT1 in cassava by molecular biological means.

Background: Perennial ryegrass (Lolium perenne L.), a widely cultivated turfgrass and forage species in Europe and North America, exhibits rapid growth and notable salt tolerance. The high-affinity potassium transporter (HKT) gene family has been implicated in salt stress responses across multiple plant species. However, whether the salt tolerance of L. perenne is closely associated with its HKT gene family remains unclear. Methods and Results: In this study, we systematically identified HKT family members in the L. perenne genome. Five HKT genes were identified and classified into three subfamilies. Among these, LpHKT1a–c exhibited canonical class I features with a conserved serine (S) residue in the P1 domain, whereas LpHKT2 belonged to class II, characterized by a glycine (G) residue in the same domain. Notably, LpHKT3 formed a distinct subfamily with a truncated structure and divergent P1/P2 domains, suggesting potential non-canonical functions. LpHKT1a likely lacked the P4 domain. Promoter analysis revealed that all five LpHKT genes contain multiple stress-related cis-acting elements. Real-time quantitative reverse transcription polymerase chain reaction results showed that LpHKT1b/c and LpHKT2 were highly expressed in both roots and leaves. Under low-concentration NaCl stress (25 mM), the expression of these three genes significantly increased by 8- to 12-fold at 6–12 h post-treatment (vs. control). Ion accumulation analysis demonstrated a rapid increase in Na+ levels following NaCl treatment, whereas K+ concentrations initially remained stable but significantly increased after 24 h. Conclusions: Combined with the cellular localization of LpHKT1c predominantly in the xylem, these findings suggest that LpHKT genes may be involved in Na+ and K+ transport in roots. This study represents the first genome-wide identification of the HKT gene family in L. perenne, providing critical insights into the molecular mechanisms underlying its salt tolerance and offering valuable genetic resources for molecular breeding aimed at enhancing stress resilience.

HAK/KUP/KT family members have been identified as playing key roles in K+ uptake and salt tolerance in numerous higher plants. However, their functions in cassava (Manihot esculenta Cantz) remain unknown. In this study, a gene encoding for a high-affinity potassium transporter (MeHAK5) was isolated from cassava and its function was investigated. Subcellular localization analysis showed that MeHAK5 is a plasma membrane-localized transporter. RT-PCR and RT-qPCR indicated that MeHAK5 is predominantly expressed in cassava roots, where it is upregulated by low potassium or high salt; in particular, its highest expression levels separately increased by 2.2 and 2.9 times after 50 µM KCl and 150 mM NaCl treatments. When heterologously expressed in yeast, MeHAK5 mediated K+ uptake within the cells of the yeast strain CY162 and rescued the salt-sensitive phenotype of AXT3K yeast. MeHAK5 overexpression in transgenic Arabidopsis plants exhibited improved growth and increased shoot K+ content under low potassium conditions. Under salt stress, MeHAK5 transgenic Arabidopsis plants accumulated more K+ in the shoots and roots and had reduced Na+ content in the shoots. As a result, MeHAK5 transgenic Arabidopsis demonstrated a more salt-tolerant phenotype. These results suggest that MeHAK5 functions as a high-affinity K+ transporter under K+ starvation conditions, improving K+/Na+ homeostasis and thereby functioning as a positive regulator of salt stress tolerance in transgenic Arabidopsis. Therefore, MeHAK5 may be a suitable candidate gene for improving K+ utilization efficiency and salt tolerance.

Plant high-affinity K⁺ transport (HKT) proteins are so named because of their relation to bacterial and fungal transporters that mediate high-affinity K⁺ uptake. The view that HKT family members are sodium-selective uniporters or sodium-potassium symporters is widely held. We have found that one of the rice HKT proteins also functions as a Ca²⁺-permeable cation channel that conducts current carried by a wide range of monovalent and divalent cations. The HKT rice gene, named OsHKT2;4, is expressed in several cell types, including root hairs and vascular parenchyma cells. The protein is localized to the plasma membrane, thereby providing a mechanism for cation uptake and extrusion. This finding goes against firmly entrenched dogma in showing that HKT proteins can function as both ion carriers and channels. The study further extends the function of HKT proteins to Ca²⁺-linked processes and, in so doing, defines a previously undescribed type of Ca²⁺-permeable cation channels in plants. The work also raises questions about the evolutionary changes in this protein family following the divergence of monocots and dicots.

The three families of yeast plasma membrane potassium influx transporters are represented in Candida albicans: Trk, Acu, and Hak proteins. Hak transporters work as K+-H+ symporters, and the genes coding for Hak proteins are transcriptionally activated under potassium limitation. This work shows that C. albicans mutant cells lacking CaHAK1 display a severe growth impairment at limiting potassium concentrations under acidic conditions. This is the consequence of a defective capacity to transport K+, as indicated by potassium absorption experiments and by the kinetics parameters of Rb+ (K+) transport. Moreover, hak1− cells are more sensitive to the toxic cation lithium. All these phenotypes became much less robust or even disappeared at alkaline growth conditions. Finally, transcriptional studies demonstrate that the hak1− mutant, in comparison with HAK1+ cells, activates the expression of the K+/Na+ ATPase coded by CaACU1 in the presence of Na+ or in the absence of K+.

Salinization of soil with sodium chloride ions inhibits plant functions, causing reduction of yield of crops. Salt tolerant microorganisms have been studied to enhance crop growth under salinity. This review describes the performance of endophytic fungi applied to crops as a supplement to plant genetics or soil management to alleviate salt stress in crops. This is achieved via inducing systemic resistance, increasing the levels of beneficial metabolites, activating antioxidant systems to scavenge ROS, and modulating plant growth phytohormones. Colonization by endophytic fungi improves nutrient uptake and maintains ionic homeostasis by modulating ion accumulation, thereby restricting the transport of Na+ to leaves and ensuring a low cytosolic Na+:K+ ratio in plants. Participating endophytic fungi enhance transcripts of genes encoding the high Affinity Potassium Transporter 1 (HKT1) and the inward-rectifying K+ channels KAT1 and KAT2, which play key roles in regulating Na+ and K+ homeostasis. Endophytic-induced interplay of strigolactones play regulatory roles in salt tolerance by interacting with phytohormones. Future research requires further attention on the biochemical, molecular and genetic mechanisms crucial for salt stress resistance requires further attention for future research. Furthermore, to design strategies for sustained plant health with endophytic fungi, a new wave of exploration of plant-endophyte responses to combinations of stresses is mandatory.

The HAK/KUP/KT transporters have been widely associated with potassium (K) transport across membranes in both microbes and plants. Here, we report the physiological function of OsHAK16, a member belonging to the HAK/KUP/KT family in rice (Oryza sativa L.). Transcriptional expression of OsHAK16 was up-regulated by K deficiency or salt stress. OsHAK16 is localized at the plasma membrane. OsHAK16 knockout (KO) dramatically reduced root K net uptake rate and growth at both 0.1 mM and 1 mM K supplies, while OsHAK16 overexpression (OX) increased total K uptake and growth only at 0.1 mM K level. OsHAK16-KO decreased the rate of rubidium (Rb) uptake and translocation compared to WT at both 0.2 mM and 1 mM Rb levels. OsHAK16 disruption decreased while its overexpression increased K concentration in root slightly but in shoot remarkably. The relative distribution of total K between shoot and root decreased by 30% in OsHAK16-KO lines and increased by 30% in its OX lines compared to WT. OsHAK16-KO diminished K uptake and K/Na ratio, while OsHAK16-OX improved K uptake and translocation from root to shoot, resulting in increased sensitivity and tolerance to salt stress, respectively. Expression of OsHAK16 enhanced the growth of high salt-sensitive yeast mutant by increasing its K but no Na content. Taking all these together, we conclude that OsHAK16 plays crucial roles in maintaining K homeostasis and salt tolerance in rice shoot.

High-affinity K(+) uptake in plants plays a crucial role in K(+) nutrition and different systems have been postulated to contribute to the high-affinity K(+) uptake. The results presented here with pepper (Capsicum annum) demonstrate that a HAK1-type transporter greatly contributes to the high-affinity K(+) uptake observed in roots. Pepper plants starved of K(+) for 3 d showed high-affinity K(+) uptake (K(m) of 6 micromolar K(+)) that was very sensitive to NH4(+) and their roots expressed a high-affinity K(+) transporter, CaHAK1, which clusters in group I of the KT/HAK/KUP family of transporters. When expressed in yeast (Saccharomyces cerevisiae), CaHAK1 mediated high-affinity K(+) and Rb(+) uptake with K(m) values of 3.3 and 1.9 micromolar, respectively. Rb(+) uptake was competitively inhibited by micromolar concentrations of NH4(+) and Cs(+), and by millimolar concentrations of Na(+).