Evolution of plant p-type ATPases

Understanding the role of P-type ATPases in regulating pollen fertility and development in pigeonpea

The P-type ATPase superfamily genes are the cation and phospholipid pumps that transport ions across the membranes by hydrolyzing ATP. They are involved in a diverse range of functions, including fundamental cellular events that occur during the growth of plants, especially in the reproductive organs. The present work has been undertaken to understand and characterize the P-type ATPases in the pigeonpea genome and their potential role in anther development and pollen fertility. A total of 59 P-type ATPases were predicted in the pigeonpea genome. The phylogenetic analysis classified the ATPases into five subfamilies: eleven P1B, eighteen P2A/B, fourteen P3A, fifteen P4, and one P5. Twenty-three pairs of P-type ATPases were tandemly duplicated, resulting in their expansion in the pigeonpea genome during evolution. The orthologs of the reported anther development-related genes were searched in the pigeonpea genome, and the expression profiling studies of specific genes via qRT-PCR in the pre- and post-meiotic anther stages of AKCMS11A (male sterile), AKCMS11B (maintainer) and AKPR303 (fertility restorer) lines of pigeonpea was done. Compared to the restorer and maintainer lines, the down-regulation of CcP-typeATPase22 in the post-meiotic anthers of the male sterile line might have played a role in pollen sterility. Furthermore, the strong expression of CcP-typeATPase2 in the post-meiotic anthers of restorer line and CcP-typeATPase46, CcP-typeATPase51, and CcP-typeATPase52 in the maintainer lines, respectively, compared to the male sterile line, clearly indicates their potential role in developing male reproductive organs in pigeonpea.

Identification of the potato (Solanum tuberosum L.) P-type ATPase gene family and investigating the role of PHA2 in response to Pep13

P-type ATPase family members play important roles in plant growth and development and are involved in plant resistance to various biotic and abiotic factors. Extensive studies have been conducted on the P-type ATPase gene families in Arabidopsis thaliana and rice but our understanding in potato remains relatively limited. Therefore, this study aimed to screen and analyze 48 P-type ATPase genes from the potato (Solanum tuberosum L.) genome database at the genome-wide level. Potato P-type ATPase genes were categorized into five subgroups based on the phylogenetic classification of the reported species. Additionally, several bioinformatic analyses, including gene structure analysis, chromosomal position analysis, and identification of conserved motifs and promoter cis-acting elements, were performed. Interestingly, the plasma membrane H+-ATPase (PM H+-ATPase) genes of one of the P3 subgroups showed differential expression in different tissues of potato. Specifically, PHA2, PHA3, and PHA7 were highly expressed in the roots, whereas PHA8 was expressed in potatoes only under stress. Furthermore, the small peptide Pep13 inhibited the expression of PHA1, PHA2, PHA3, and PHA7 in potato roots. Transgenic plants heterologously overexpressing PHA2 displayed a growth phenotype sensitive to Pep13 compared with wild-type plants. Further analysis revealed that reducing potato PM H+-ATPase enzyme activity enhanced resistance to Pep13, indicating the involvement of PM H+-ATPase in the physiological process of potato late blight and the enhancement of plant disease resistance. This study confirms the critical role of potato PHA2 in resistance to Pep13.

Glomus versiforme and intercropping with Sphagneticola calendulacea decrease Cd accumulation in maize

Little information is available on the influence of the compound use of intercropping (IN) and arbuscular mycorrhizal fungus (AMF) on Cd accumulation and the expression of Cd transporter genes in two intercropped plants. A pot experiment was conducted to study the influences of IN and AMF-Glomus versiforme on growth and Cd uptake of two intercropped plants-maize and Cd hyperaccumulator Sphagneticola calendulacea, and the expression of Cd transporter genes in maize in Cd-polluted soils. IN, AMF and combined treatments of IN and AMF (IN + AMF) obviously improved biomass, photosynthesis and total antioxidant capacities of two plants. Moreover, single and compound treatments of IN and AMF evidently reduced Cd contents in maize, and the greatest decreases appeared in the compound treatment. However, Cd contents of S. calendulacea in IN, AMF and IN + AMF groups were notably improved. Furthermore, the single and compound treatments of IN and AMF significantly downregulated the expression levels of Nramp1, HMA1, ABCC1 and ABCC10 in roots and leaves, and the largest decreases were observed in the combined treatment. Our work first revealed that the combined use of IN and AMF appeared to have a synergistic effect on decreasing Cd content by downregulating the expression of Cd transporter genes in maize.

Plasma membrane H+-ATPases in mineral nutrition and crop improvement

Plasma membrane H+-ATPases (PMAs) pump H+ out of the cytoplasm by consuming ATP to generate a membrane potential and proton motive force for the transmembrane transport of nutrients into and out of plant cells. PMAs are involved in nutrient acquisition by regulating root growth, nutrient uptake, and translocation, as well as the establishment of symbiosis with arbuscular mycorrhizas. Under nutrient stresses, PMAs are activated to pump more H+ and promote organic anion excretion, thus improving nutrient availability in the rhizosphere. Herein we review recent progress in the physiological functions and the underlying molecular mechanisms of PMAs in the efficient acquisition and utilization of various nutrients in plants. We also discuss perspectives for the application of PMAs in improving crop production and quality.

Light-induced stomatal opening requires phosphorylation of the C-terminal autoinhibitory domain of plasma membrane H+-ATPase

Plasma membrane H+-ATPase provides the driving force for light-induced stomatal opening. However, the mechanisms underlying the regulation of its activity remain unclear. Here, we show that the phosphorylation of two Thr residues in the C-terminal autoinhibitory domain is crucial for H+-ATPase activation and stomatal opening in Arabidopsis thaliana. Using phosphoproteome analysis, we show that blue light induces the phosphorylation of Thr-881 within the C-terminal region I, in addition to penultimate Thr-948 in AUTOINHIBITED H+-ATPASE 1 (AHA1). Based on site-directed mutagenesis experiments, phosphorylation of both Thr residues is essential for H+ pumping and stomatal opening in response to blue light. Thr-948 phosphorylation is a prerequisite for Thr-881 phosphorylation by blue light. Additionally, red light-driven guard cell photosynthesis induces Thr-881 phosphorylation, possibly contributing to red light-dependent stomatal opening. Our findings provide mechanistic insights into H+-ATPase activation that exploits the ion transport across the plasma membrane and light signalling network in guard cells.

OsACA9, an Autoinhibited Ca2+-ATPase, Synergically Regulates Disease Resistance and Leaf Senescence in Rice

Calcium (Ca2+) is a versatile intracellular second messenger that regulates several signaling pathways involved in growth, development, stress tolerance, and immune response in plants. Autoinhibited Ca2+-ATPases (ACAs) play an important role in the regulation of cellular Ca2+ homeostasis. Here, we systematically analyzed the putative OsACA family members in rice, and according to the phylogenetic tree of OsACAs, OsACA9 was clustered into a separated branch in which its homologous gene in Arabidopsis thaliana was reported to be involved in defense response. When the OsACA9 gene was knocked out by CRISPR/Cas9, significant accumulation of reactive oxygen species (ROS) was detected in the mutant lines. Meanwhile, the OsACA9 knock out lines showed enhanced disease resistance to both rice bacterial blight (BB) and bacterial leaf streak (BLS). In addition, compared to the wild-type (WT), the mutant lines displayed an early leaf senescence phenotype, and the agronomy traits of their plant height, panicle length, and grain yield were significantly decreased. Transcriptome analysis by RNA-Seq showed that the differentially expressed genes (DEGs) between WT and the Osaca9 mutant were mainly enriched in basal immune pathways and antibacterial metabolite synthesis pathways. Among them, multiple genes related to rice disease resistance, receptor-like cytoplasmic kinases (RLCKs) and cell wall-associated kinases (WAKs) genes were upregulated. Our results suggest that the Ca2+-ATPase OsACA9 may trigger oxidative burst in response to various pathogens and synergically regulate disease resistance and leaf senescence in rice.

A two-sequence motif-based method for the inventory of gene families in fragmented and poorly annotated genome sequences

Databases of genome sequences are growing exponentially, but, in some cases, assembly is incomplete and genes are poorly annotated. For evolutionary studies, it is important to identify all members of a given gene family in a genome. We developed a method for identifying most, if not all, members of a gene family from raw genomes in which assembly is of low quality, using the P-type ATPase superfamily as an example. The method is based on the translation of an entire genome in all six reading frames and the co-occurrence of two family-specific sequence motifs that are in close proximity to each other. To test the method's usability, we first used it to identify P-type ATPase members in the high-quality annotated genome of barley (Hordeum vulgare). Subsequently, after successfully identifying plasma membrane H+-ATPase family members (P3A ATPases) in various plant genomes of varying quality, we tested the hypothesis that the number of P3A ATPases correlates with the ability of the plant to tolerate saline conditions. In 19 genomes of glycophytes and halophytes, the total number of P3A ATPase genes was found to vary from 7 to 22, but no significant difference was found between the two groups. The method successfully identified P-type ATPase family members in raw genomes that are poorly assembled.

Regulation of a vacuolar proton-pumping P-ATPase MdPH5 by MdMYB73 and its role in malate accumulation and vacuolar acidification

As the main organic acid in fruits, malate is produced in the cytoplasm and is then transported into the vacuole. It accumulates by vacuolar proton pumps, transporters, and channels, affecting the taste and flavor of fruits. Among the three types of proton pumps (V-ATPases, V-PPases, and P-ATPases), the P-ATPases play an important role in the transport of malate into vacuoles. In this study, the transcriptome data, collected at different stages after blooming and during storage, were analyzed and the results demonstrated that the expression of MdPH5, a vacuolar proton-pumping P-ATPase, was associated with both pre- and post-harvest malate contents. Moreover, MdPH5 is localized at the tonoplast and regulates malate accumulation and vacuolar pH. In addition, MdMYB73, an upstream MYB transcription factor of MdPH5, directly binds to its promoter, thereby transcriptionally activating its expression and enhancing its activity. In this way, MdMYB73 can also affect malate accumulation and vacuolar pH. Overall, this study clarifies how MdMYB73 and MdPH5 act to regulate vacuolar malate transport systems, thereby affecting malate accumulation and vacuolar pH.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00115-7.

The conserved evolution of plant H+-ATPase family and the involvement of soybean H+-ATPases in sodium bicarbonate stress responses

Plant plasma membrane (PM) H+-ATPases are essential pumps involved in multiple physiological processes. They play a significant role in regulating pH homeostasis and membrane potential by generating the electrochemical gradient of the proton across the plasma membrane. However, information on soybean PM H+-ATPase is still limited. In this study, we conducted the evolutionary analysis of PM H+-ATPases in land plants and investigated the subfamily classification and whole genome duplication of PM H+-ATPases in angiosperms. We further characterized the extremely high conservation of the soybean PM H+-ATPase family in terms of gene structure, domain architecture, and protein sequence identity. Using the yeast system, we confirmed the highly conserved biochemical characteristics (14-3-3 binding affinity and pump activity) of soybean PM H+-ATPases and their conserved function in enhancing tolerance to high pH and NaHCO3 stresses. Meanwhile, our results also revealed their divergence in the transcriptional expression in different tissues and under sodium bicarbonate stress. Finally, the function of soybean PM H+-ATPases in conferring sodium bicarbonate tolerance was validated using transgenic Arabidopsis. Together, these results conclude that the soybean PM H+-ATPase is evolutionarily conserved and positively regulates the response to sodium bicarbonate stress.

Evolution of the sodium pump

Eukaryotic plasma membranes (PMs) are energized by electrogenic P-type ATPases that generate either Na+ or H+ motive forces to drive Na+ and H+ dependent transport processes, respectively. For this purpose, animal rely on Na+/K+-ATPases whereas fungi and plants employ PM H+-ATPases. Prokaryotes, on the other hand, depend on H+ or Na+-motive electron transport complexes to energize their cell membranes. This raises the question as to why and when electrogenic Na+ and H+ pumps evolved? Here it is shown that prokaryotic Na+/K+-ATPases have near perfect conservation of binding sites involved in coordination of three Na+ and two K+ ions. Such pumps are rare in Eubacteria but are common in methanogenic Archaea where they often are found together with P-type putative PM H+-ATPases. With some exceptions, Na+/K+-ATPases and PM H+-ATPases are found everywhere in the eukaryotic tree of life, but never together in animals, fungi and land plants. It is hypothesized that Na+/K+-ATPases and PM H+-ATPases evolved in methanogenic Archaea to support the bioenergetics of these ancestral organisms, which can utilize both H+ and Na+ as energy currencies. Both pumps must have been simultaneously present in the first eukaryotic cell, but during diversification of the major eukaryotic kingdoms, and at the time animals diverged from fungi, animals kept Na+/K+-ATPases but lost PM H+-ATPases. At the same evolutionary branch point, fungi did loose Na+/K+-ATPases, and their role was taken over by PM H+-ATPases. An independent but similar scenery emerged during terrestrialization of plants: they lost Na+/K+-ATPases but kept PM H+-ATPases.

Energy crosstalk between photosynthesis and the algal CO2-concentrating mechanisms

Microalgal photosynthesis is responsible for nearly half of the CO2 annually captured by Earth's ecosystems. In aquatic environments where the CO2 availability is low, the CO2-fixing efficiency of microalgae greatly relies on mechanisms - called CO2-concentrating mechanisms (CCMs) - for concentrating CO2 at the catalytic site of the CO2-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). While the transport of inorganic carbon (Ci) across membrane bilayers against a concentration gradient consumes part of the chemical energy generated by photosynthesis, the bioenergetics and cellular mechanisms involved are only beginning to be elucidated. Here, we review the current knowledge relating to the energy requirement of CCMs in the light of recent advances in photosynthesis regulatory mechanisms and the spatial organization of CCM components.

Significance and genetic control of membrane transporters to improve phytoremediation and biofortification processes

Humans frequently consume plant-based foods in their daily life. Contamination of agricultural soils by heavy metals (HMs) is a major food and nutritional security issue. The crop plants grown in HM-contaminated agricultural soil may accumulate more HMs in their edible part, further transferring into the food chain. Consumption of HM-rich crops can cause severe health issues in humans. On the other hand, the low content of the essential HM in the edible part of the crop also causes health problems. Therefore, researchers must try to reduce the non-essential HM in the edible part of the crop plants and improve the essential HMs. Phytoremediation and biofortification are the two strategies for resolving this problem. The genetic component helps to improve the efficiency of phytoremediation and biofortification processes in plants. They help eliminate HMs from soil and improve essential HM content in crop plants. The membrane transporter genes (genetic components) are critical in these two strategies. Therefore, engineering membrane transporter genes may help reduce the non-essential HM content in the edible part of crop plants. Targeted gene editing by genome editing tools like CRISPR could help plants achieve efficient phytoremediation and biofortification. This article covers gene editing's scope, application, and implication to improve the phytoremediation and biofortification processes in non-crop and crop plants.

Vacuolar MATE/DTX protein-mediated cucurbitacin C transport is co-regulated with bitterness biosynthesis in cucumber

Membrane-localized transporters constitute important components for specialized metabolism in plants. However, due to the vast array of specialized metabolites produced by plants, and the large families of transporter genes, knowledge about the intracellular and intercellular transport of plant metabolites is still in its infancy. Cucurbitacins are bitter and defensive triterpenoids produced mainly in the cucurbits. Using a comparative genomics and multi-omics approach, a MATE gene (CsMATE1), physically clustered with cucurbitacin C (CuC) biosynthetic genes, was identified and functionally shown to sequester CuC in cucumber leaf mesophyll cells. Notably, the CuC transport process is strictly co-regulated with CuC biosynthesis. CsMATE1 clustering with bitterness biosynthesis genes may provide benefits and a basis for this feedback regulation on CuC sequestration and biosynthesis. Identification of transport systems for plant-specialized metabolites can accelerate the metabolic engineering of high-value-added compounds by simplifying their purification process.

Copper toxicity compromises root acquisition of nitrate in the high affinity range

The application of copper (Cu)-based fungicides for crop protection plans has led to a high accumulation of Cu in soils, especially in vineyards. Copper is indeed an essential micronutrient for plants, but relatively high concentrations in soil or other growth substrates may cause toxicity phenomena, such as alteration of the plant's growth and disturbance in the acquisition of mineral nutrients. This last aspect might be particularly relevant in the case of nitrate ( NO 3 - ) , whose acquisition in plants is finely regulated through the transcriptional regulation of NO 3 - transporters and plasma membrane H⁺-ATPase in response to the available concentration of the nutrient. In this study, cucumber plants were grown hydroponically and exposed to increasing concentrations of Cu (i.e., 0.2, 5, 20, 30, and 50 µM) to investigate their ability to respond to and acquire NO 3 - . To this end, the kinetics of substrate uptake and the transcriptional modulation of the molecular entities involved in the process have been assessed. Results showed that the inducibility of the high-affinity transport system was significantly affected by increasing Cu concentrations; at Cu levels higher than 20 µM, plants demonstrated either strongly reduced or abolished NO 3 - uptake activity. Nevertheless, the transcriptional modulation of both the nitrate transporter CsNRT2.1 and the accessory protein CsNRT3.1 was not coherent with the hindered NO 3 - uptake activity. On the contrary, CsHA2 was downregulated, thus suggesting that a possible impairment in the generation of the proton gradient across the root PM could be the cause of the abolishment of NO 3 - uptake.

Na + /K + -ATPase regulates the K + /Na + homeostasis in the intertidal macroalgae, Neoporphyra haitanensis, in response to salt stress

In plants under hypersaline stress, the main transporter that extrudes sodium ions (Na ⁺ ) is the Na ⁺ /H ⁺ antiporter SOS1. Different from land plants, the intertidal macroalgae, Neopyropia/Neoporphyra contains an animal-type Na ⁺ /K ⁺ -ATPase as well as the SOS1 system. However, the contribution of Na ⁺ /K ⁺ -ATPase to the K ⁺ /Na ⁺ homeostasis of intertidal macroalgae remains unclear. In this study, we analyzed the function of Na ⁺ /K ⁺ -ATPase in the response of Neoporphyra haitanensis to salt stress from the perspective of ion transport dynamics. Both the transcript level of NhNKA2 and enzyme activity of Na ⁺ /K ⁺ -ATPase increased in the early response of N. haitanensis thalli to hypersaline stress. Addition of ouabain, an inhibitor of Na ⁺ /K ⁺ -ATPase, resulted in Na ⁺ accumulation in the cells, severe K ⁺ leakage from the thalli, and then remarkably disturbed the K ⁺ /Na ⁺ homeostasis in N. haitanensis thalli. This disruption might induce a significant decrease in photosynthesis and a severe oxidative damage in thalli. Accordingly, these results suggested that the important role of Na ⁺ /K ⁺ -ATPase in the resistance of intertidal macroalgae to hypersaline stress, and shed light on the diversity of K ⁺ /Na ⁺ homeostasis maintenance mechanisms in plants.

Genome-wide analysis elucidates the roles of GhHMA genes in different abiotic stresses and fiber development in upland cotton

The heavy metal-binding domain is involved in heavy metal transporting and plays a significant role in plant detoxification. However, the functions of HMAs are less well known in cotton. In this study, a total of 143 GhHMAs (heavy metal-binding domain) were detected by genome-wide identification in G. hirsutum L. All the GhHMAs were classified into four groups via phylogenetic analysis. The exon/intron structure and protein motifs indicated that each branch of the GhHMA genes was highly conserved. 212 paralogous GhHMA gene pairs were identified, and the segmental duplications were the main role to the expansion of GhHMAs. The Ka/Ks values suggested that the GhHMA gene family has undergone purifying selection during the long-term evolutionary process. GhHMA3 and GhHMA75 were located in the plasma membrane, while GhHMA26, GhHMA117 and GhHMA121 were located in the nucleus, respectively. Transcriptomic data and qRT-PCR showed that GhHMA26 exhibited different expression patterns in each tissue and during fiber development or under different abiotic stresses. Overexpressing GhHMA26 significantly promoted the elongation of leaf trichomes and also improved the tolerance to salt stress. Therefore, GhHMA26 may positively regulate fiber elongation and abiotic stress. Yeast two-hybrid assays indicated that GhHMA26 and GhHMA75 participated in multiple biological functions. Our results suggest some genes in the GhHMAs might be associated with fiber development and the abiotic stress response, which could promote further research involving functional analysis of GhHMA genes in cotton.

Structural Analysis and Diversity of Calmodulin-Binding Domains in Membrane and Intracellular Ca2+-ATPases

The plasma membrane and autoinhibited Ca²⁺-ATPases contribute to the Ca²⁺ homeostasis in a wide variety of organisms. The enzymatic activity of these pumps is stimulated by calmodulin, which interacts with the target protein through the calmodulin-binding domain (CaMBD). Most information about this region is related to all calmodulin modulated proteins, which indicates general chemical properties and there is no established relation between Ca²⁺ pump sequences and taxonomic classification. Thus, the aim of this study was to perform an in silico analysis of the CaMBD from several Ca²⁺-ATPases, in order to determine their diversity and to detect specific patterns and amino acid selection in different species. Patterns related to potential and confirmed CaMBD were detected using sequences retrieved from the literature. The occurrence of these patterns was determined across 120 sequences from 17 taxonomical classes, which were analyzed by a phylogenetic tree to establish phylogenetic groups. Predicted physicochemical characteristics including hydropathy and net charge were calculated for each group of sequences. 22 Ca²⁺-ATPases sequences from animals, unicellular eukaryotes, and plants were retrieved from bioinformatic databases. These sequences allow us to establish the Patterns 1(GQILWVRGLTRLQTQ), 3(KNPSLEALQRW), and 4(SRWRRLQAEHVKK), which are present at the beginning of putative CaMBD of metazoan, parasites, and land plants. A pattern 2 (IRVVNAFR) was consistently found at the end of most analyzed sequences. The amino acid preference in the CaMBDs changed depending on the phylogenetic groups, with predominance of several aliphatic and charged residues, to confer amphiphilic properties. The results here displayed show a conserved mechanism to contribute to the Ca²⁺ homeostasis across evolution and may help to detect putative CaMBDs.

Structure, Function, and Applications of Soybean Calcium Transporters

Glycine max is a calcium-loving crop. The external application of calcium fertilizer is beneficial to the increase of soybean yield. Indeed, calcium is a vital nutrient in plant growth and development. As a core metal ion in signaling transduction, calcium content is maintained in dynamic balance under normal circumstances. Now, eight transporters were found to control the uptake and efflux of calcium. Though these calcium transporters have been identified through genome-wide analysis, only a few of them were functionally verified. Therefore, in this study, we summarized the current knowledge of soybean calcium transporters in structural features, expression characteristics, roles in stress response, and prospects. The above results will be helpful in understanding the function of cellular calcium transport and provide a theoretical basis for elevating soybean yield.

Genome-Wide Identification and Characterization of Banana Ca2+-ATPase Genes and Expression Analysis under Different Concentrations of Ca2+ Treatments

Ca²⁺-ATPases have been confirmed to play very important roles in plant growth and development and in stress responses. However, studies on banana (Musa acuminata) Ca²⁺-ATPases are very limited. In this study, we identified 18 Ca²⁺-ATPase genes from banana, including 6 P-IIA or ER (Endoplasmic Reticulum) type Ca²⁺-ATPases (MaEACs) and 12 P-IIB or Auto-Inhibited Ca²⁺-ATPases (MaACAs). The MaEACs and MaACAs could be further classified into two and three subfamilies, respectively. This classification is well supported by their gene structures, which are encoded by protein motif distributions. The banana Ca²⁺-ATPases were all predicted to be plasma membrane-located. The promoter regions of banana Ca²⁺-ATPases contain many cis-acting elements and transcription factor binding sites (TFBS). A gene expression analysis showed that banana Ca²⁺-ATPases were differentially expressed in different organs. By investigating their expression patterns in banana roots under different concentrations of Ca²⁺ treatments, we found that most banana Ca²⁺-ATPase members were highly expressed under 4 mM and 2 mM Ca²⁺ treatments, but their expression decreased under 1 mM and 0 mM Ca²⁺ treatments, suggesting that their downregulation might be closely related to reduced Ca accumulation and retarded growth under low Ca²⁺ and Ca²⁺ deficiency conditions. Our study will contribute to the understanding of the roles of Ca²⁺-ATPases in banana growth and Ca management.

Two plant growth-promoting bacterial Bacillus strains possess different mechanisms in affecting cadmium uptake and detoxification of Solanum nigrum L

Microorganisms affect cadmium (Cd) extraction by hyperaccumulators to varying degrees, but the potential mechanism has not been completely studied. Here, two plant growth-promoting bacteria (PGPB, Bacillus paranthracis NT1 and Bacillus megaterium NCT-2) were assessed for their influence on Cd uptake by Solanum nigrum L. and their influence mechanisms. The results showed that both two strains could regulate phytohormones secretion, alleviate oxidative stress and promote S. nigrum growth when exposed to Cd (dry weight was significantly increased by 21.51% (strain NCT-2) and 21.23% (strain NT1) compared with the control, respectively). Additionally, strain NCT-2 significantly elevated the translocation factor (TF) and bioconcentration factor (BCF), and thus significantly facilitated total Cd uptake by 41.80% of S. nigrum, whereas strain NT1 significantly reduced the BCF and TF, resulting in insignificant effect on total Cd uptake of S. nigrum compared with the control. Results of qPCR illustrated that the two strains influenced the detoxification of Cd in S. nigrum by affecting the expression of antioxidant enzyme genes and gene PDR2. Moreover, the differential expression of heavy metal transport genes IRT1 and HMA may lead to the difference of Cd accumulation in S. nigrum. Principal component analysis and Pearson correlation coefficient analysis further verified the positive roles of salicylic acid and indole-3-acetic acid on Cd detoxification of S. nigrum, and the positive correlation relationship between transportation of Cd from underground to shoot, plant biomass and Cd uptake. Altogether, our results demonstrated that these two PGPB have great potential in helping plants detoxify Cd and could provide insights into the mechanism of PGPB-assisted phytoremediation of Cd-contaminated soil.

Tripartite hormonal regulation of plasma membrane H+-ATPase activity

The enzyme activity of the plasma membrane (PM) proton pump, well known as arabidopsis PM H⁺-ATPase (AHA) in the model plant arabidopsis (Arabidopsis thaliana), is controlled by phosphorylation. Three different classes of phytohormones, brassinosteroids (BRs), abscisic acid (ABA), and auxin regulate plant growth and responses to environmental stimuli, at least in part by modulating the activity of the pump through phosphorylation of the penultimate Thr residue in its carboxyl terminus. Here, we review the current knowledge regarding this tripartite hormonal AHA regulation and highlight mechanisms of activation and deactivation, as well as the significance of hormonal crosstalk. Understanding the complexity of PM H⁺-ATPase regulation in plants might provide new strategies for sustainable agriculture.

Evolutionary and Regulatory Pattern Analysis of Soybean Ca2+ ATPases for Abiotic Stress Tolerance

P₂-type Ca²⁺ ATPases are responsible for cellular Ca²⁺ transport, which plays an important role in plant development and tolerance to biotic and abiotic stresses. However, the role of P₂-type Ca²⁺ ATPases in stress response and stomatal regulation is still elusive in soybean. In this study, a total of 12 P₂-type Ca²⁺ ATPases genes (GmACAs and GmECAs) were identified from the genome of Glycine max. We analyzed the evolutionary relationship, conserved motif, functional domain, gene structure and location, and promoter elements of the family. Chlorophyll fluorescence imaging analysis showed that vegetable soybean leaves are damaged to different extents under salt, drought, cold, and shade stresses. Real-time quantitative PCR (RT-qPCR) analysis demonstrated that most of the GmACAs and GmECAs are up-regulated after drought, cold, and NaCl treatment, but are down-regulated after shading stress. Microscopic observation showed that different stresses caused significant stomatal closure. Spatial location and temporal expression analysis suggested that GmACA8, GmACA9, GmACA10, GmACA12, GmACA13, and GmACA11 might promote stomatal closure under drought, cold, and salt stress. GmECA1 might regulate stomatal closure in shading stress. GmACA1 and GmECA3 might have a negative function on cold stress. The results laid an important foundation for further study on the function of P₂-type Ca²⁺ ATPase genes GmACAs and GmECAs for breeding abiotic stress-tolerant vegetable soybean.

Heavy metal transporters: Functional mechanisms, regulation, and application in phytoremediation

Heavy metal pollution in soil is a global problem with serious impacts on human health and ecological security. Phytoextraction in phytoremediation, in which plants uptake and transport heavy metals (HMs) to the tissues of aerial parts, is the most environmentally friendly method to reduce the total amount of HMs in soil and has wide application prospects. However, the molecular mechanism of phytoextraction is still under investigation. The uptake, translocation, and retention of HMs in plants are mainly mediated by a variety of transporter proteins. A better understanding of the accumulation strategy of HMs via transporters in plants is a prerequisite for the improvement of phytoextraction. In this review, the biochemical structure and functions of HM transporter families in plants are systematically summarized, with emphasis on their roles in phytoremediation. The accumulation mechanism and regulatory pathways related to hormones, regulators, and reactive oxygen species (ROS) of HMs concerning these transporters are described in detail. Scientific efforts and practices for phytoremediation carried out in recent years suggest that creation of hyperaccumulators by transgenic or gene editing techniques targeted to these transporters and their regulators is the ultimate powerful path for the phytoremediation of HM contaminated soils.

Posttranslational regulation of transporters important for symbiotic interactions

Coordinated sharing of nutritional resources is a central feature of symbiotic interactions, and, despite the importance of this topic, many questions remain concerning the identification, activity, and regulation of transporter proteins involved. Recent progress in obtaining genome and transcriptome sequences for symbiotic organisms provides a wealth of information on plant, fungal, and bacterial transporters that can be applied to these questions. In this update, we focus on legume-rhizobia and mycorrhizal symbioses and how transporters at the symbiotic interfaces can be regulated at the protein level. We point out areas where more research is needed and ways that an understanding of transporter mechanism and energetics can focus hypotheses. Protein phosphorylation is a predominant mechanism of posttranslational regulation of transporters in general and at the symbiotic interface specifically. Other mechanisms of transporter regulation, such as protein-protein interaction, including transporter multimerization, polar localization, and regulation by pH and membrane potential are also important at the symbiotic interface. Most of the transporters that function in the symbiotic interface are members of transporter families; we bring in relevant information on posttranslational regulation within transporter families to help generate hypotheses for transporter regulation at the symbiotic interface.

Mechanisms and regulation of organic acid accumulation in plant vacuoles

In fleshy fruits, organic acids are the main source of fruit acidity and play an important role in regulating osmotic pressure, pH homeostasis, stress resistance, and fruit quality. The transport of organic acids from the cytosol to the vacuole and their storage are complex processes. A large number of transporters carry organic acids from the cytosol to the vacuole with the assistance of various proton pumps and enzymes. However, much remains to be explored regarding the vacuolar transport mechanism of organic acids as well as the substances involved and their association. In this review, recent advances in the vacuolar transport mechanism of organic acids in plants are summarized from the perspectives of transporters, channels, proton pumps, and upstream regulators to better understand the complex regulatory networks involved in fruit acid formation.

Natural variations in the P-type ATPase heavy metal transporter gene ZmHMA3 control cadmium accumulation in maize grains

Cadmium (Cd) accumulation in maize grains is detrimental to human health. Developing maize varieties with low Cd content is important for safe consumption of maize grains. However, the key genes controlling maize grain Cd accumulation have not been cloned. Here, we identified one major locus for maize grain Cd accumulation (qCd1) using a genome-wide association study (GWAS) and bulked segregant RNA-seq analysis with a biparental segregating population of Jing724 (low-Cd line) and Mo17 (high-Cd line). The candidate gene ZmHMA3 was identified by fine mapping and encodes a tonoplast-localized heavy metal P-type ATPase transporter. An ethyl methane sulfonate mutant analysis and an allelism test confirmed that ZmHMA3 influences maize grain Cd accumulation. A transposon in intron 1 of ZmHMA3 is responsible for the abnormal amino acid sequence in Mo17. Based on the natural sequence variations in the ZmHMA3 gene of diverse maize lines, four PCR-based molecular markers were developed, and these were successfully used to distinguish five haplotypes with different grain Cd contents in the GWAS panel and to predict grain Cd contents of widely used maize inbred lines and hybrids. These molecular markers can be used to breed elite maize varieties with low grain Cd contents.

Partial cloning, characterization, and analysis of expression and activity of plasma membrane H+-ATPase in Kallar grass [Leptochloa fusca (L.) Kunth] under salt stress

Kallar grass (Leptochloa fusca) is a highly salt-tolerant C4 perennial halophytic forage. The regulation of ion movement across the plasma membrane (PM) to improve salinity tolerance of plant is thought to be accomplished with the aid of the proton electrochemical gradient generated by PM H⁺-ATPase. In this study, we cloned a partial gene sequence of the Lf PM H⁺-ATPase and investigated its expression and activity under salt stress. The amino acid sequence of the isolated region of Lf PM H⁺-ATPase possesses the maximum identity up to 96% to its ortholog in Aeluropus littoralis. The isolated fragment of Lf PM H⁺-ATPase gene is a member of the subfamily Π of plant PM H⁺-ATPase and is most closely related to the Oryza sativa gene OSA7. The transcript level and activity of the PM H⁺-ATPase were increased in roots and shoots in response to NaCl and were peaked at 450 mM NaCl in both tissues. The induction of activity and gene expression of PM H⁺-ATPase in roots and shoots of Kallar grass under salinity indicate the necessity for this pump in these organs during salinity adaptation to establish and maintain the electrochemical gradient across the PM of the cells for adjusting ion homeostasis.

Molecular regulation of zinc deficiency responses in plants

Zinc (Zn) is an essential micronutrient for plants and animals. Because of its low availability in arable soils worldwide, Zn deficiency is becoming a serious agricultural problem resulting in decreases of crop yield and nutritional quality. Plants have evolved multiple responses to adapt to low levels of soil Zn supply, involving biochemical and physiological changes to improve Zn acquisition and utilization, and defend against Zn deficiency stress. In this review, we summarize the physiological and biochemical adaptations of plants to Zn deficiency, the roles of transporters and metal-binding compounds in Zn homeostasis regulation, and the recent progresses in understanding the sophisticated regulatory mechanisms of Zn deficiency responses that have been made by molecular and genetic analyses, as well as diverse 'omics' studies. Zn deficiency responses are tightly controlled by multiple layers of regulation, such as transcriptional regulation that is mediated by transcription factors like F-group bZIP proteins, epigenetic regulation at the level of chromatin, and post-transcriptional regulation mediated by small RNAs and alternative splicing. The insights into the regulatory network underlying Zn deficiency responses and the perspective for further understandings of molecular regulation of Zn deficiency responses have been discussed. The understandings of the regulatory mechanisms will be important for improving Zn deficiency tolerance, Zn use efficiency, and Zn biofortification in plants.

High external Na+, but not K+, stimulates the growth of Ulva lactuca (L.) via induction of the plasma membrane ATPases and achievement of K+/Na+ homeostasis

This study aims at investigating the specific ion effects of Na⁺ and K⁺ on Ulva lactuca (L.) growth. U. lactuca was grown in balanced nutrient solutions with 10, 100, 300 and 600 mM NaCl or KCl. The growth was significantly higher at 300 and 600 mM NaCl compared to KCl, with the highest growth rate at 300 mM NaCl. NaCl-treated alga showed increases in the photosynthetic pigments and Rubisco protein content. However, KCl treatments adversely affected these photosynthetic attributes. U. lactuca needs adjusted, but not high K⁺/Na⁺ ratio for a proper growth, since the high K⁺/Na⁺ ratio in KCl-treated alga was associated with growth retardation. The cell wall was more extensible at high concentrations of NaCl compared to KCl. Therefore, the deleterious effect of K⁺ could be mainly on the cell wall and hence inhibiting the growth and perhaps the vitality of the whole cell. The transcript of plasma membrane (PM) H⁺-ATPase was detected only at 300 and 600 mM NaCl, implying that this gene was specifically induced by high concentrations of Na⁺ but not K⁺. The transcript of PM-Na⁺/K⁺-ATPase-like exhibited no Na⁺ specificity and its induction alone could not improve the growth of KCl-treated U. lactuca. The simultaneous induction of the two PM-ATPases could positively affect the algal growth at high NaCl concentrations by maintaining the proper cellular K⁺/Na⁺ ratio. Also, both PM-ATPases might contribute to energizing the plasma membrane and thereby promoting the cellular growth of U. lactuca at high Na⁺, but not K⁺, concentrations.

Arabidopsis Ca2+-ATPases 1, 2, and 7 in the endoplasmic reticulum contribute to growth and pollen fitness

Generating cellular Ca2+ signals requires coordinated transport activities from both Ca2+ influx and efflux pathways. In Arabidopsis (Arabidopsis thaliana), multiple efflux pathways exist, some of which involve Ca2+-pumps belonging to the Autoinhibited Ca2+-ATPase (ACA) family. Here, we show that ACA1, 2, and 7 localize to the endoplasmic reticulum (ER) and are important for plant growth and pollen fertility. While phenotypes for plants harboring single-gene knockouts (KOs) were weak or undetected, a triple KO of aca1/2/7 displayed a 2.6-fold decrease in pollen transmission efficiency, whereas inheritance through female gametes was normal. The triple KO also resulted in smaller rosettes showing a high frequency of lesions. Both vegetative and reproductive phenotypes were rescued by transgenes encoding either ACA1, 2, or 7, suggesting that all three isoforms are biochemically redundant. Lesions were suppressed by expression of a transgene encoding NahG, an enzyme that degrades salicylic acid (SA). Triple KO mutants showed elevated mRNA expression for two SA-inducible marker genes, Pathogenesis-related1 (PR1) and PR2. The aca1/2/7 lesion phenotype was similar but less severe than SA-dependent lesions associated with a double KO of vacuolar pumps aca4 and 11. Imaging of Ca2+ dynamics triggered by blue light or the pathogen elicitor flg22 revealed that aca1/2/7 mutants display Ca2+ transients with increased magnitudes and durations. Together, these results indicate that ER-localized ACAs play important roles in regulating Ca2+ signals, and that the loss of these pumps results in male fertility and vegetative growth deficiencies.

Electrogenesis in Plasma Membrane Fraction of Halotolerant Microalga Dunaliella maritima and Effects of N,N'-Dicyclohexylcarbodiimide

The effects of N,N'-dicyclohexylcarbodiimide (DCCD), non-specific inhibitor of various transport systems functioning in biological membranes, on Na+-transporting P-type ATPase of the green halotolerant microalga Dunaliella maritima were studied in the experiments with vesicular plasma membranes isolated from the alga cells. The effects of DCCD on electrogenic/ion transport function of the enzyme and its ATP hydrolase activity were investigated. Electrogenic/ion transport function of the enzyme was recorded as a Na+-dependent generation of electric potential on the vesicle membranes with the help of the potential-sensitive probe oxonol VI. It was found that unlike many other ion-transporting ATPases, the Na+-ATPase of D. maritima is insensitive to DCCD. This agent did not inhibit either ATP hydrolysis catalyzed by this enzyme or its transport activity. At the same time DCCD affected the ability of the vesicle membranes to maintain electric potential generated by the D. maritima Na+-ATPase. The observed effects can be explained based on the assumption that DCCD interacts with the Na+/H+ antiporter in the plasma membrane of D. maritima.

Evolution of Plant Na+-P-Type ATPases: From Saline Environments to Land Colonization

Soil salinity is one of the major factors obstructing the growth and development of agricultural crops. Eukaryotes have two main transport systems involved in active Na⁺ removal: cation/H⁺ antiporters and Na⁺-P-type ATPases. Key transport proteins, Na⁺/K⁺-P-ATPases, are widely distributed among the different taxa families of pumps which are responsible for keeping cytosolic Na⁺ concentrations below toxic levels. Na⁺/K⁺-P-ATPases are considered to be absent in flowering plants. The data presented here are a complete inventory of P-type Na⁺/K⁺-P-ATPases in the major branches of the plant kingdom. We also attempt to elucidate the evolution of these important membrane pumps in plants in comparison with other organisms. We were able to observe the gradual replacement of the Na+-binding site to the Ca²⁺-binding site, starting with cyanobacteria and moving to modern land plants. Our results show that the α-subunit likely evolved from one common ancestor to bacteria, fungi, plants, and mammals, whereas the β-subunit did not evolve in green algae. In conclusion, our results strongly suggest the significant differences in the domain architecture and subunit composition of plant Na⁺/K⁺-P-ATPases depending on plant taxa and the salinity of the environment. The obtained data clarified and broadened the current views on the evolution of Na⁺/K⁺-P-ATPases. The results of this work would be helpful for further research on P-type ATPase functionality and physiological roles.

Involvement of plasma membrane H+-ATPase in diamide-induced extracellular alkalization by roots from pea seedlings

MAIN CONCLUSION

The plasma membrane H+-ATPase can be considered as a redox-dependent enzyme, because diamide-mediated inhibition of its hydrolytic and transport activities is accompanied by alkalization of the rhizosphere and retardation of root growth. Plasma membranes were isolated from roots of etiolated pea seedlings treated in the presence of an oxidant-diamide and an inhibitor of redox-sensitive protein phosphatase-phenylarsine oxide. Hydrolytic and proton transport activities of H+-ATPase were determined. The effects of diamide appeared in inhibition of both ATP hydrolysis and the proton transport. However, root treatment with phenylarsine oxide only slightly reduced Vmax, but did not affect ATP-dependent proton transport. The thiol groups of cysteines in the proteins can act as molecular targets for both compounds. However, treatment of isolated membranes with diamide or dithiothreitol did not have any effect on the H+ transport. It can be assumed that water-soluble diamide acts indirectly and its effects are not associated with oxidation of H+-ATPase cysteines. Therefore, plasmalemma was subjected to PEGylation-process where reduced cysteines available for PEG maleimide (5 kDa) were alkylated. Detection of such cysteines was carried out by Western blot analysis with anti-ATPase antibodies. It was found that shifts in the apparent molecular weight were detected only for denaturated proteins. These data suggest that available thiols are not localized on the enzyme surfaces. BN-PAGE analysis showed that the molecular weights of the ATPase complexes are almost identical in all samples. Therefore, oligomerization is probably not the reason for the inhibition of ATPase activity. Roots treated with these inhibitors in vivo exhibited stunted growth; however, a strong alkaline zone around the roots was formed only in the presence of diamide. Involvement of H+-ATPase redox regulation in this process is discussed.

The copper economy response is partially conserved in rice (Oryza sativa L.)

Copper (Cu) is an essential element for plants, especially in photosynthesis, as it is required for plastocyanin function in electron transfer reactions at thylakoid membranes. In Arabidopsis thaliana, Cu deficiency leads to the Cu economy response, in which plants prioritize Cu usage by plastocyanin in detriment of non-essential cupric proteins. In rice (Oryza sativa), however, this response has not been characterized. Rice OsHMA5 is a Cu xylem-loading transporter involved in Cu translocation from roots to shoots, as suggested by the analysis of oshma5 mutant plants. Aiming to understand how rice plants respond to Cu deficiency and how decreased Cu translocation to shoots can affect this response, we characterized the physiological and molecular responses of WT and oshma5 plants under control and Cu deficiency treatments. We found evidence that shoots of oshma5 plants are more prone to Cu deficiency compared to shoots of WT plants, as demonstrated by decreased chlorophyll and Cu concentrations, and electron transport rate. Gene expression analysis revealed that Cu high-affinity transporters OsCOPT1 and OsCOPT5, along with a set of miRNAs and three Cu/Zn superoxide dismutases are responsive to Cu deficiency in both WT and oshma5 plants, suggesting their involvement in the Cu economy response. However, Fe superoxide dismutase was not up-regulated in rice, indicating a difference compared to the A. thaliana Cu economy model. Therefore, we provide evidence for a partially conserved Cu economy response in rice, in comparison to A. thaliana.

Identification of MAMP-Responsive Plasma Membrane-Associated Proteins in Arabidopsis thaliana Following Challenge with Different LPS Chemotypes from Xanthomonas campestris

Lipopolysaccharides (LPS) are recognized as microbe-associated molecular patterns (MAMPs) responsible for eliciting defense-related responses and while the effects have been well-documented in mammals, there is a lack of knowledge regarding the mechanism of perception in plant systems and recognized structural moieties within the macromolecular lipoglycan structure. Thus, identification of the LPS plasma membrane (PM) receptor(s)/receptor complex in Arabidopsis thaliana through proteomics will contribute to a deeper understanding of induced defense responses. As such, structurally characterized LPS chemotypes from Xanthomonas campestris pv. campestris (Xcc) wild-type 8004 (prototypical smooth-type LPS) and mutant 8530 (truncated core with no O–chain) strains were utilized to pre-treat A. thaliana plants. The associated proteomic response/changes within the PM were compared over a 24 h period using mass spectrometry-based methodologies following three variants of LPS-immobilized affinity chromatography. This resulted in the identification of proteins from several functional categories, but importantly, those involved in perception and defense. The distinct structural features between wild-type and mutant LPS are likely responsible for the differential changes to the proteome profiles, and many of the significant proteins were identified in response to the wild-type Xcc LPS where it is suggested that the core oligosaccharide and O-chain participate in recognition by receptor-like kinases (RLKs) in a multiprotein complex and, notably, varied from that of the mutant chemotype.

Plant glucose transporter structure and function

The carbohydrate D-glucose is the main source of energy in living organisms. In contrast to animals, as well as most fungi, bacteria, and archaea, plants are capable to synthesize a surplus of sugars characterizing them as autothrophic organisms. Thus, plants are de facto the source of all food on earth, either directly or indirectly via feed to livestock. Glucose is stored as polymeric glucan, in animals as glycogen and in plants as starch. Despite serving a general source for metabolic energy and energy storage, glucose is the main building block for cellulose synthesis and represents the metabolic starting point of carboxylate- and amino acid synthesis. Finally yet importantly, glucose functions as signalling molecule conveying the plant metabolic status for adjustment of growth, development, and survival. Therefore, cell-to-cell and long-distance transport of photoassimilates/sugars throughout the plant body require the fine-tuned activity of sugar transporters facilitating the transport across membranes. The functional plant counterparts of the animal sodium/glucose transporters (SGLTs) are represented by the proton-coupled sugar transport proteins (STPs) of the plant monosaccharide transporter(-like) family (MST). In the framework of this special issue on “Glucose Transporters in Health and Disease,” this review gives an overview of the function and structure of plant STPs in comparison to the respective knowledge obtained with the animal Na⁺-coupled glucose transporters (SGLTs).

Heavy Metal Stress-Associated Proteins in Rice and Arabidopsis: Genome-Wide Identification, Phylogenetics, Duplication, and Expression Profiles Analysis

Heavy metal exposure is a serious environmental stress in plants. However, plants have evolved several strategies to improve their heavy metal tolerance. Heavy metal-associated proteins (HMPs) participate in heavy metal detoxification. Here, we identified 46 and 55 HMPs in rice and Arabidopsis, respectively, and named them OsHMP 1–46 and AtHMP 1–55 according to their chromosomal locations. The HMPs from both plants were divided into six clades based on the characteristics of their heavy metal-associated domains (HMA). The HMP gene structures and motifs varied greatly among the different classifications. The HMPs had high collinearity and were segmentally duplicated. A cis-element analysis revealed that the HMPs may be regulated by different transcription factors. An expression profile analysis disclosed that only eight OsHMPs were constitutive in rice tissues. Of these, the expression of OsHMP37 was far higher than that of the other seven genes while OsHMP28 was expressed exclusively in the roots. For Arabidopsis, nine AtHMPs presented with very high transcript levels in all organs. Most of the selected OsHMPs were differentially expressed in various tissues under different heavy metal stresses. Only OsHMP09, OsHMP18, and OsHMP22 showed higher expression levels in all tissues under different heavy metal stresses. In contrast, most of the selected AtHMPs had nearly constant expression levels in different tissues under various heavy metal stresses. The AtHMP20, AtHMP23, AtHMP25, AtHMP31, AtHMP35, AtHMP46 expression levels under different heavy metal stresses were higher in the leaves and roots. The foregoing discoveries elucidated HMP evolution in monocotyledonous and dicotyledonous plants and may helpful functionally characterize HMPs in the future.

Expression of three P4-phospholipid flippases-atp11a, atp11b, and atp11c in zebrafish (Danio rerio)

Cellular membrane asymmetry is a hallmark characteristic of all eukaryotic cells. The balance of phospholipid composition within the cytoplasmic inner leaflet and the extracellular outer leaflet of the plasma membrane (PM) maintains cellular function and vitality. The proper exposure of particular phospholipids is necessary to maintain cellular signalling, controlled apoptosis, and vesicle transportation among other roles. Phospholipid asymmetry is coordinated by P4-type phospholipid transferases (flippases or ATPases). ATP11A, ATP11B, and ATP11C belong to class VI of the P4-flippase family (vertebrates) and are responsible for the movement of phosphatidylserine (PS) from the outer leaflet to the inner leaflet of the PM. To date, there is a lack of knowledge of the tissue specific expression of these three flippases on a whole-organism level in a vertebrate system. Here we have determined the spatial-temporal expression profiles of each gene in a zebrafish model using in situ hybridization and performed comparative phylogenetic analyses with other vertebrates. Our data reveals sequence similarity between vertebrate flippases and specific synteny of zebrafish and human chromosomes. Both atp11b and atp11c are maternally expressed in zebrafish, while zygotic expression analysis demonstrates tissue and temporal specificity for all three genes. atp11a is expressed in the neural crest cells as well as in the developing eye and ear, while atp11b is expressed early in the ventricular epithelial lining and later in the ear. atp11c is expressed in the anterior most rhombomeres of the hindbrain, pharyngeal arches, and liver. Our expression data suggests that each of the three flippases are integral for the development of specific tissues, and aberrant function of either could lead to visual, hearing, neural, or liver dysfunction.

Genome-Wide Identification and Characterization of Apple P3A-Type ATPase Genes, with Implications for Alkaline Stress Responses

The P3A-type ATPases play crucial roles in various physiological processes via the generation of a transmembrane H+ gradient (∆pH). However, the P3A-type ATPase superfamily in apple remains relatively uncharacterized. In this study, 15 apple P3A-type ATPase genes were identified based on the new GDDH13 draft genome sequence. The exon-intron organization of these genes, the physical and chemical properties, and conserved motifs of the encoded enzymes were investigated. Analyses of the chromosome localization and ω values of the apple P3A-type ATPase genes revealed the duplicated genes were influenced by purifying selection pressure. Six clades and frequent old duplication events were detected. Moreover, the significance of differences in the evolutionary rates of the P3A-type ATPase genes were revealed. An expression analysis indicated that all of the P3A-type ATPase genes were specifically expressed in more than one tissue. The expression of one P3A-type ATPase gene (MD15G1108400) was significantly upregulated in response to alkaline stress. Furthermore, a subcellular localization assay indicated that MD15G1108400 is targeted to the plasma membrane. These results imply that MD15G1108400 may be involved in responses to alkaline stress. Our data provide insights into the molecular characteristics and evolutionary patterns of the apple P3A-type ATPase gene family and provide a theoretical foundation for future in-depth functional characterizations of P3A-type ATPase genes under alkaline conditions.

Plant Membrane Transport Research in the Post-genomic Era

Membrane transport processes are indispensable for many aspects of plant physiology including mineral nutrition, solute storage, cell metabolism, cell signaling, osmoregulation, cell growth, and stress responses. Completion of genome sequencing in diverse plant species and the development of multiple genomic tools have marked a new era in understanding plant membrane transport at the mechanistic level. Genes coding for a galaxy of pumps, channels, and carriers that facilitate various membrane transport processes have been identified while multiple approaches are developed to dissect the physiological roles as well as to define the transport capacities of these transport systems. Furthermore, signaling networks dictating the membrane transport processes are established to fully understand the regulatory mechanisms. Here, we review recent research progress in the discovery and characterization of the components in plant membrane transport that take advantage of plant genomic resources and other experimental tools. We also provide our perspectives for future studies in the field.

Regulatory mechanisms underlying the maintenance of homeostasis in Pyropia haitanensis under hypersaline stress conditions

Intertidal macroalgae are highly resistant to hypersaline stress conditions. However, the underlying mechanism remains unknown. In the present study, the mechanism behind Pyropia haitanensis responses to two hypersaline stress conditions [100‰ (HSS_100) and 110‰ (HSS_110)] was investigated via analyses of physiological and transcriptomic changes. We observed that the differences between the responses of Py. haitanensis to HSS_100 and HSS_110 conditions involved the following three aspects: osmotic regulation, ionic homeostasis, and adjustment to secondary stresses. First, the water retention of Py. haitanensis was maintained through increased expansin production under HSS_100 conditions, while cell wall pectin needed to be protected from hydrolysis via the increased abundance of a pectin methylesterase inhibitor under HSS_110 conditions. Meanwhile, Py. haitanensis achieved stable and rapid osmotic adjustments because of the coordinated accumulation of inorganic ions (K⁺, Na⁺, and Cl^-) and organic osmolytes (glycine betaine and trehalose) under HSS_100 conditions, but not under HSS_110 conditions. Second, Py. haitanensis maintained a higher K⁺/Na⁺ ratio under HSS_100 conditions than under HSS_110 conditions, mainly via the export of Na⁺ into the apoplast rather than compartmentalizing it into the vacuoles, and the enhanced uptake and retention of K⁺. However, K⁺/Na⁺ homeostasis was not completely disrupted during a short-term exposure to HSS_110 conditions. Finally, the Py. haitanensis antioxidant system scavenged more ROS and synthesized more heat shock proteins under HSS_100 conditions than under HSS_110 conditions, although thalli may have been able to maintain a certain redox balance during a short-term exposure to HSS_110 conditions. These differences may explain why Py. haitanensis can adapt to HSS_100 conditions rather than HSS_110 conditions, and also why the thalli exposed to HSS_110 conditions can recover after being transferred to normal seawater. Thus, the data presented herein may elucidate the mechanisms enabling Pyropia species to tolerate the sudden and periodic changes in salinity typical of intertidal systems.

Transcriptome analysis revealed pivotal transporters involved in the reduction of cadmium accumulation in pak choi (Brassica chinensis L.) by exogenous hydrogen-rich water

Hydrogen-rich water (HRW) has been widely used in research on plant resistance to Cd. However, the underlying molecular mechanism of HRW in ameliorating cadmium stress in vegetables is largely unknown. In this study, the RNA-sequencing analyses were used to characterize the role of HRW in the alleviation of Cd toxicity in Chinese cabbage seedlings. Based on the obtained results, two genes encoding metal ionic transporters, BcIRT1 and BcZIP2 were ultimately selected out. Then, a systematic validation of the metal ion transport function of these two ZIP-encoding genes of pak choi were performed via a yeast transformation system. The results showed that BcIRT1 and BcZIP2 increased the sensitivity of different yeast mutant strains to relative metal ionic stresses and facilitated the accumulation of metal ions (Cd²⁺, Mn²⁺, Zn²⁺, and Fe²⁺) in yeast; thus, it suggests that BcIRT1 and BcZIP2 probably have the ability to transport Cd²⁺, Mn²⁺, Zn²⁺ and Fe²⁺ in pak choi. The time-course and concentration-dependent expression profiles of BcIRT1 and BcZIP2 showed that as time with HRW increased, the effectiveness of the repression on the expression of BcIRT1 and BcZIP2 increased, and as the seedlings were exposed to increased Cd concentrations, the inhibition of BcIRT1 and BcZIP2 by HRW was also increased. Over all, these findings provide new insights into the genome-wide transcriptome profiles in pak choi and show that HRW reduced Cd uptake probably through inhibiting the expression of transporters related to Cd absorption, BcIRT1 and BcZIP2.

Homology modeling and in vivo functional characterization of the zinc permeation pathway in a heavy metal P-type ATPase

The P1B ATPase heavy metal ATPase 4 (HMA4) is responsible for zinc and cadmium translocation from roots to shoots in Arabidopsis thaliana. It couples ATP hydrolysis to cytosolic domain movements, enabling metal transport across the membrane. The detailed mechanism of metal permeation by HMA4 through the membrane remains elusive. Here, homology modeling of the HMA4 transmembrane region was conducted based on the crystal structure of a ZntA bacterial homolog. The analysis highlighted amino acids forming a metal permeation pathway, whose importance was subsequently investigated functionally through mutagenesis and complementation experiments in plants. Although the zinc pathway displayed overall conservation among the two proteins, significant differences were observed, especially in the entrance area with altered electronegativity and the presence of a ionic interaction/hydrogen bond network. The analysis also newly identified amino acids whose mutation results in total or partial loss of the protein function. In addition, comparison of zinc and cadmium accumulation in shoots of A. thaliana complemented lines revealed a number of HMA4 mutants exhibiting different abilities in zinc and cadmium translocation. These observations could be instrumental to design low cadmium-accumulating crops, hence decreasing human cadmium exposure.

Evolutionary and Functional Analysis of a Chara Plasma Membrane H+-ATPase

H⁺-ATPases are the main transporters in plant and fungal plasma membranes (PMs), comparable to the Na⁺/K⁺ ATPases in animal cells. At the molecular level, most studies on the PM H⁺-ATPases have been focused on land plants and fungi (yeast). The research of PM H⁺-ATPases in green algae falls far behind due to the lack of genetic information. Here we studied a potential PM H⁺-ATPase (CHA1) from Chara australis, a species of green algae belonging to the division Charophyta, members of which are considered to be one of the closest ancestors of land plants. The gene encodes a 107 kDa protein with all 6 P-type ATPase-specific motifs and a long, diverse C-terminal domain. A new amino acid sequence motif R*****Q in transmembrane segment 5 was identified among the known PM H⁺-ATPases from Charophyta and Chlorophyta algae, which is different from the typical PM H⁺-ATPases in yeast or land plants. Complementation analysis in yeast showed that CHA1 could successfully reach the PM, and that proton pump activity was obtained when the last 77 up to 87 amino acids of the C-terminal domain were deleted. PM localization was confirmed in Arabidopsis protoplasts; however, deletion of more than 55 amino acids at the N-terminus or more than 98 amino acids at the C-terminus resulted in failure of CHA1 to reach the PM in yeast. These results suggest that an auto-inhibition domain is located in the C-terminal domain, and that CHA1 is likely to have a different regulation mechanism compared to the yeast and land plant PM H⁺-ATPases.