ZMK1 Is Involved in K+ Uptake and Regulated by Protein Kinase ZmCIPK23 in Zea mays

Dissecting the genetic architecture of polygenic nutritional traits in maize through meta-QTL analysis

Maize, as a staple crop, contributes significantly to global nutritional security. However, improving its nutritional quality, including grain zinc (GZn), grain iron (GFe), kernel oil (KO), protein quality (PQ), and content (PC), is difficult due to the complex and polygenic nature of these traits. In traditional quantitative trait loci (QTLs) mapping, different populations tested across variable environments have resulted in heterogeneous findings, highlighting the challenge of QTL instability. Therefore, we tested whether Meta-QTL (MQTL) analysis enables the identification of stable QTLs with broader allelic coverage and higher mapping resolution for effective marker-assisted selection (MAS) of complex traits. A comprehensive literature search revealed 29 mapping studies encompassing 308 QTLs for the targeted traits. A total of 34 stable MQTLs were identified, with an average CI of 4.59 cM. These MQTLs were located on all ten maize chromosomes, with phenotypic variance explained (PVE %) ranging from 7.3 % (MQTL1_2) to 49.0 % (MQTL3_2). Furthermore, the analysis revealed six MAS-friendly and five hotspot MQTLs. Besides, 591 CGs were identified underlying these MQTLs, of which 14 have known roles in grain filling, metal homeostasis, and fatty acid biosynthesis in maize. In silico analysis confirmed the tissue-specific expression of these 14 CGs. MQTL analysis effectively refined the genomic regions (4.86 folds) linked with nutritional quality and identified stable MQTLs and CGs. These findings will be useful for developing nutritionally enriched varieties through MAS and genetic engineering.

GmAKT1-mediated K+ absorption positively modulates soybean salt tolerance by GmCBL9-GmCIPK6 complex

Soybean is one of the most important crops in the world. However, salt stress poses a major challenge to soybean growth and productivity. Therefore, unravelling the complex mechanisms governing salt tolerance in soybean is imperative for molecular breeding of salt-tolerant varieties to improve yield. Maintaining intracellular Na+/K+ homeostasis is one of the key factors for plant salt tolerance. Although some salt tolerance mechanisms involving Na+ exclusion have been well identified in plants, few studies have been conducted on how K+ influx controls soybean salt tolerance. Here, we characterized the function of soybean K+ channel gene GmAKT1 and identified GmCBL9-GmCIPK6 complex, which modulated GmAKT1-mediated K+ uptake under salt stress. Functional studies found that soybean lines GmAKT1 overexpressing increased K+ content and promoted salt tolerance, while CRISPR/Cas9-mediated disruption of GmAKT1 soybean lines decreased the K+ content and showed salt sensitivity. Furthermore, we identified that GmCIPK6 interacted with GmAKT1 and GmCBL9 interacted with GmCIPK6. In addition, Mn2+-Phos-tag assays proved that GmCIPK6 could phosphorylate GmAKT1. This collaborative activation of the GmCBL9-GmCIPK6-GmAKT1 module promoted K+ influx and enhanced soybean salt tolerance. Our findings reveal a new molecular mechanism in soybeans under salt stress and provide insights for cultivating new salt-tolerant soybean varieties by molecular breeding.

Metal ion transport in maize: survival in a variable stress environment

Maize (Zea mays) is the most widely cultivated crop in the world. Maize production is closely linked to the extensive uptake and utilization of various mineral nutrients. Potassium (K), calcium (Ca), and magnesium (Mg) are essential metallic macronutrients for plant growth and development. Sodium (Na) is an essential micronutrient for some C4 and CAM plants. Several metallic micronutrients like iron (Fe), manganese (Mn), and zinc (Zn) serve as enzyme components or co-factors in plant cells. Maize has to face the combined ion stress conditions in the natural environment. The limited availability of these nutrients in soils restricts maize production. In saline land, excessive Na could inhibit the uptake of mineral elements. Additionally, aluminum (Al) and heavy metals cadmium (Cd) and lead (Pb) in soils are toxic to maize and pose a threat to food security. Thus, plants must evolve complex mechanisms to increase nutrient uptake and utilization while restraining harmful elements. This review summarizes the research progress on the uptake and transport of metal ions in maize, highlights the regulation mechanism of metal ion transporters under stress conditions, and discusses the future challenges for the improvement of maize with high nutrient utilization efficiency (NUE).

Research Progress on Plant Shaker K+ Channels

Plant growth and development are driven by intricate processes, with the cell membrane serving as a crucial interface between cells and their external environment. Maintaining balance and signal transduction across the cell membrane is essential for cellular stability and a host of life processes. Ion channels play a critical role in regulating intracellular ion concentrations and potentials. Among these, K+ channels on plant cell membranes are of paramount importance. The research of Shaker K+ channels has become a paradigm in the study of plant ion channels. This study offers a comprehensive overview of advancements in Shaker K+ channels, including insights into protein structure, function, regulatory mechanisms, and research techniques. Investigating Shaker K+ channels has enhanced our understanding of the regulatory mechanisms governing ion absorption and transport in plant cells. This knowledge offers invaluable guidance for enhancing crop yields and improving resistance to environmental stressors. Moreover, an extensive review of research methodologies in Shaker K+ channel studies provides essential reference solutions for researchers, promoting further advancements in ion channel research.

Inhibition of SlSKOR by SlCIPK23-SlCBL1/9 uncovers CIPK-CBL-target network rewiring in land plants

Transport of K⁺ to the xylem is a key process in the mineral nutrition of the shoots. Although CIPK-CBL complexes have been widely shown to regulate K⁺ uptake transport systems, no information is available about the xylem ones. Here, we studied the physiological roles of the voltage-gated K⁺ channel SlSKOR and its regulation by the SlCIPK23-SlCBL1/9 complexes in tomato plants. We phenotyped gene-edited slskor and slcipk23 tomato knockout mutants and carried out two-electrode voltage-clamp (TEVC) and BiFC assays in Xenopus oocytes as key approaches. SlSKOR was preferentially expressed in the root stele and was important not only for K⁺ transport to shoots but also, indirectly, for that of Ca²⁺ , Mg²⁺ , Na⁺ , NO₃ ^- , and Cl^- . Surprisingly, the SlCIPK23-SlCBL1/9 complexes turned out to be negative regulators of SlSKOR. Inhibition of SlSKOR by SlCIPK23-SlCBL1/9 was observed in Xenopus oocytes and tomato plants. Regulation of SKOR-like channels by CIPK23-CBL1 complexes was also present in Medicago, grapevine, and lettuce but not in Arabidopsis and saltwater cress. Our results provide a molecular framework for coordinating root K⁺ uptake and its translocation to the shoot by SlCIPK23-SlCBL1/9 in tomato plants. Moreover, they evidenced that CIPK-CBL-target networks have evolved differently in land plants.

Structural basis for the activity regulation of a potassium channel AKT1 from Arabidopsis

The voltage-gated potassium channel AKT1 is responsible for primary K⁺ uptake in Arabidopsis roots. AKT1 is functionally activated through phosphorylation and negatively regulated by a potassium channel α-subunit AtKC1. However, the molecular basis for the modulation mechanism remains unclear. Here we report the structures of AKT1, phosphorylated-AKT1, a constitutively-active variant, and AKT1-AtKC1 complex. AKT1 is assembled in 2-fold symmetry at the cytoplasmic domain. Such organization appears to sterically hinder the reorientation of C-linkers during ion permeation. Phosphorylated-AKT1 adopts an alternate 4-fold symmetric conformation at cytoplasmic domain, which indicates conformational changes associated with symmetry switch during channel activation. To corroborate this finding, we perform structure-guided mutagenesis to disrupt the dimeric interface and identify a constitutively-active variant Asp379Ala mediates K⁺ permeation independently of phosphorylation. This variant predominantly adopts a 4-fold symmetric conformation. Furthermore, the AKT1-AtKC1 complex assembles in 2-fold symmetry. Together, our work reveals structural insight into the regulatory mechanism for AKT1.

Arabidopsis thaliana potassium channel AKT1 is responsible for primary K + uptake from soil, which is functionally activated through phosphorylation and negatively regulated by an α-subunit AtKC1. Here, the authors report the structures of AKT1 at different states, revealing a 2- fold to 4-fold symmetry switch at cytoplasmic domain associated with AKT1 activity regulation.

Potassium in plants: Growth regulation, signaling, and environmental stress tolerance

Potassium (K) is an essential element for the growth and development of plants; however, its scarcity or excessive level leads to distortion of numerous functions in plants. It takes part in the control of various significant functions in plant advancement. Because of the importance index, K is regarded second after nitrogen for whole plant growth. Approximately, higher than 60 enzymes are reliant on K for activation within the plant system, in which K plays a vital function as a regulator. Potassium provides assistance in plants against abiotic stress conditions in the environment. With this background, the present paper reviews the physiological functions of K in plants like stomatal regulation, photosynthesis and water uptake. The article also focuses upon the uptake and transport mechanisms of K along with its role in detoxification of reactive oxygen species and in conferring tolerance to plants against abiotic stresses. It also highlights the research progress made in the direction of K mediated signaling cascades.