Genome-Wide Identification and Analysis of P-Type Plasma Membrane H+-ATPase Sub-Gene Family in Sunflower and the Role of HHA4 and HHA11 in the Development of Salt Stress Resistance

A Limited Number of Amino Acid Permeases Are Crucial for Cryptococcus neoformans Survival and Virulence

One unique attribute of Cryptococcus neoformans is its ability to procure essential monomers from its surroundings to survive in diverse environments. Preferentially, sugars are the energy sources for this opportunistic pathogenic fungus under the carbon catabolite repression (CCR); however, sugar restriction induces alternative use of low molecular weight alcohol, organic acids, and amino acids. The expression of transmembrane amino acid permeases (Aaps) allows C. neoformans to utilize different amino acids and their conjugates, notwithstanding under the nitrogen catabolite repression (NCR). Being referred to as global permeases, there is a notion that all cryptococcal Aaps are important to survival and virulence. This functional divergence makes alternative drug targeting against Cryptococcus a challenge. We examine the functions and regulations of C. neoformans Aap variants with the aim of rationalizing their relevance to cryptococcal cell survival and virulence. Based on nutrient bioavailability, we linked the Cac1 pathway to Ras1 activation for thermotolerance that provides a temperature cushion for Aap activity under physiological conditions. Lastly, mutants of Aaps are examined for significant phenotypic deficiencies/advantages, which buttress the specific importance of limited numbers of Aaps involved in cryptococcal infections.

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.

The asymmetric expression of plasma membrane H+-ATPase family genes in response to pulvinus-driven leaf phototropism movement in Vitis vinifera

Phototropism movement is crucial for plants to adapt to various environmental changes. Plant P-type H+-ATPase (HA) plays diverse roles in signal transduction during cell expansion, regulation of cellular osmotic potential and stomatal opening, and circadian movement. Despite numerous studies on the genome-wide analysis of Vitis vinifera, no research has been done on the P-type H+-ATPase family genes, especially concerning pulvinus-driven leaf movement. In this study, 55 VvHAs were identified and classified into nine distinct subgroups (1 to 9). Gene members within the same subgroups exhibit similar features in motif, intron/exon, and protein tertiary structures. Furthermore, four pairs of genes were derived by segmental duplication in grapes. Cis-acting element analysis identified numerous light/circadian-related elements in the promoters of VvHAs. qRT-PCR analysis showed that several genes of subgroup 7 were highly expressed in leaves and pulvinus during leaf movement, especially VvHA14, VvHA15, VvHA16, VvHA19, VvHA51, VvHA52, and VvHA54. Additionally, we also found that the VvHAs genes were asymmetrically expressed on both sides of the extensor and flexor cell of the motor organ, the pulvinus. The expression of VvHAs family genes in extensor cells was significantly higher than that in flexor cells. Overall, this study serves as a foundation for further investigations into the functions of VvHAs and contributes to the complex mechanisms underlying grapevine pulvinus growth and development.

Identification and characterization of the plasma membrane H+-ATPase genes in Brassica napus and functional analysis of BnHA9 in salt tolerance

As a primary proton pump, plasma membrane (PM) H+-ATPase plays critical roles in regulating plant growth, development, and stress responses. PM H+-ATPases have been well characterized in many plant species. However, no comprehensive study of PM H+-ATPase genes has been performed in Brassica napus (rapeseed). In this study, we identified 32 PM H+-ATPase genes (BnHAs) in the rapeseed genome, and they were distributed on 16 chromosomes. Phylogenetical and gene duplication analyses showed that the BnHA genes were classified into five subfamilies, and the segmental duplication mainly contributed to the expansion of the rapeseed PM H+-ATPase gene family. The conserved domain and subcellular analyses indicated that BnHAs encoded canonical PM H+-ATPase proteins with 14 highly conserved domains and localized on PM. Cis-acting regulatory element and expression pattern analyses indicated that the expression of BnHAs possessed tissue developmental stage specificity. The 25 upstream open reading frames with the canonical initiation codon ATG were predicted in the 5' untranslated regions of 11 BnHA genes and could be used as potential target sites for improving rapeseed traits. Protein interaction analysis showed that BnBRI1.c associated with BnHA2 and BnHA17, indicating that the conserved activity regulation mechanism of BnHAs may be present in rapeseed. BnHA9 overexpression in Arabidopsis enhanced the salt tolerance of the transgenic plants. Thus, our results lay a foundation for further research exploring the biological functions of PM H+-ATPases in rapeseed.

Hydrogen sulfide improves salt tolerance through persulfidation of PMA1 in Arabidopsis

KEY MESSAGE

A new interaction was found between PMA1 and GRF4. H₂S promotes the interaction through persulfidated Cys446 of PMA1. H₂S activates PMA1 to maintain K⁺/Na⁺ homeostasis through persulfidation under salt stress. Plasma membrane H⁺-ATPase (PMA) is a transmembrane transporter responsible for pumping protons, and its contribution to salt resistance is indispensable in plants. Hydrogen sulfide (H₂S), a small signaling gas molecule, plays the important roles in facilitating adaptation of plants to salt stress. However, how H₂S regulates PMA activity remains largely unclear. Here, we show a possible original mechanism for H₂S to regulate PMA activity. PMA1, a predominant member in the PMA family of Arabidopsis, has a non-conservative persulfidated cysteine (Cys) residue (Cys446), which is exposed on the surface of PMA1 and located in cation transporter/ATPase domain. A new interaction of PMA1 and GENERAL REGULATORY FACTOR 4 (GRF4, belongs to the 14-3-3 protein family) was found by chemical crosslinking coupled with mass spectrometry (CXMS) in vivo. H₂S-mediated persulfidation promoted the binding of PMA1 to GRF4. Further studies showed that H₂S enhanced instantaneous H⁺ efflux and maintained K⁺/Na⁺ homeostasis under salt stress. In light of these findings, we suggest that H₂S promotes the binding of PMA1 to GRF4 through persulfidation, and then activating PMA, thus improving the salt tolerance of Arabidopsis.

Regulation of Cytosolic pH: The Contributions of Plant Plasma Membrane H+-ATPases and Multiple Transporters

Cytosolic pH homeostasis is a precondition for the normal growth and stress responses in plants, and H+ flux across the plasma membrane is essential for cytoplasmic pH control. Hence, this review focuses on seven types of proteins that possess direct H+ transport activity, namely, H+-ATPase, NHX, CHX, AMT, NRT, PHT, and KT/HAK/KUP, to summarize their plasma-membrane-located family members, the effect of corresponding gene knockout and/or overexpression on cytosolic pH, the H+ transport pathway, and their functional regulation by the extracellular/cytosolic pH. In general, H+-ATPases mediate H+ extrusion, whereas most members of other six proteins mediate H+ influx, thus contributing to cytosolic pH homeostasis by directly modulating H+ flux across the plasma membrane. The fact that some AMTs/NRTs mediate H+-coupled substrate influx, whereas other intra-family members facilitate H+-uncoupled substrate transport, demonstrates that not all plasma membrane transporters possess H+-coupled substrate transport mechanisms, and using the transport mechanism of a protein to represent the case of the entire family is not suitable. The transport activity of these proteins is regulated by extracellular and/or cytosolic pH, with different structural bases for H+ transfer among these seven types of proteins. Notably, intra-family members possess distinct pH regulatory characterization and underlying residues for H+ transfer. This review is anticipated to facilitate the understanding of the molecular basis for cytosolic pH homeostasis. Despite this progress, the strategy of their cooperation for cytosolic pH homeostasis needs further investigation.

Comparative transcriptome analysis reveals the molecular mechanism of salt tolerance in Apocynum venetum

Apocynum venetum is a traditional Chinese medicinal herb with tolerance to various abiotic stresses, especially, salinity. However, only a few studies have investigated the salt-tolerant mechanism of this non-halophyte under salt stress at phenotypic and physiological levels. To explore the molecular mechanism of salinity tolerance in A. venetum, the global transcriptome profiles of seedling leaves under different salt-stress durations, using 200 mM NaCl, were analyzed. De novo assembly of approximately 715 million high-quality reads and approximately 105.61 Gb sequence data was performed. In total, 2822 differentially expressed genes (DEGs) were identified. DEGs were significantly enriched in flavonoid metabolism-related pathways such as "flavonoid biosynthesis" and "phenylpropanoid biosynthesis". Most of these DEGs were downregulated under salt stress. However, genes encoding the non-selective cation channels and antioxidants were upregulated under salt stress, whereas most cell wall-related DEGs were downregulated. Consequently, the concentration of flavonoids decreased, whereas that of Na⁺ increased with exposure time. Thus, we hypothesized that the accumulation of Na⁺ in the leaves, which resulted in reduced flavonoid concentration under salt stress, directly led to a decrease in the salt tolerance of A. venetum. This was verified by overexpressing four flavonoid synthesis pathway genes in Arabidopsis. The transgenic plants showed higher salt tolerance than the wild-type plants due to the accumulation of total flavonoids. These physiological and transcriptome analyses of A. venetum revealed major molecular underpinnings contributing to the responses of A. venetum to salt stress, thereby improving our understanding of the molecular mechanisms underlying salt tolerance in A. venetum and plants in general. The findings serve as a basis for functional studies on and engineering strategies for plant salinity tolerance.

Transcription Factor CsWRKY65 Participates in the Establishment of Disease Resistance of Citrus Fruits to Penicillium digitatum

Penicillium digitatum is the primary pathogen that causes serious yield losses worldwide. In our previous study, CsWRKY transcription factors (TFs) and some genes associated with immunity were identified in citrus fruits after P. digitatum infection, but little information is available in the literature on the mechanisms of TFs in citrus disease resistance. In this study, the possible mechanisms of CsWRKY65 participating in the establishment of disease resistance were investigated. Results show that CsWRKY65 was a transcriptional activator in the nucleus. The dual-luciferase transient assays and electrophoretic mobility shift assays showed that CsWRKY65 bound with CsRbohB, CsRbohD, CsCDPK33, and CsPR10 promoters to activate gene transcription. Besides, the transient overexpression of CsWRKY65 induced reactive oxygen species accumulation and increased PR gene expression in Nicotiana benthamiana leaves. The transient overexpression of CsWRKY65 in the citrus peel enhanced the disease resistance against P. digitatum. In conclusion, CsWRKY65 is likely to be involved in regulating the disease resistance to P. digitatum of citrus fruits by directly activating the expressions of CsRbohB, CsRbohD, CsCDPK33, and CsPR10. This study provides new information for the mechanism of citrus WRKY TFs participating in the establishment of disease resistance.

Overexpression of an Apocynum venetum flavonols synthetase gene confers salinity stress tolerance to transgenic tobacco plants

Soil salinity is a major limiting factor for agricultural production, threatening food security worldwide. A thorough understanding of the mechanisms underlying plant responses is required to effectively counter its deleterious effects on crop productivity. Total flavonoid accumulation reportedly improves salinity tolerance in many crops. Therefore, we isolated the full-length cDNA of a flavonol synthetase (FLS) gene from Apocynum venetum (AvFLS). The gene contained a 1008-bp open reading frame encoding a protein composed of 335 amino acid residues. Multiple sequence alignment showed that the AvFLS protein was highly homologous to FLSs from other plants. AvFLS was expressed in leaves, stems, roots, flowers, and germinated seeds. Expression pattern analysis revealed that AvFLS was significantly induced by salinity stress. AvFLS overexpression in tobacco positively affected the development and growth of transgenic plants under salinity stress: root and seedling growth were inhibited to a lesser extent, while seed germination rate increased. Additionally, the overexpression of AvFLS under salinity stress resulted in an increase in total flavonoid content (1.63 mg g-1 in wild-type samples and 4.63 mg g-1 on average in transgenic samples), which accompanied the increase in the activity of antioxidant enzymes and inhibited the production of reactive oxygen species. Further, AvFLS-overexpressing transgenic tobacco plants absorbed more K+ than wild type plants, leading to an increased K+/Na+ ratio, which in turn contributed to the maintenance of Na+/K+ homeostasis. These findings suggest that an AvFLS-induced increase in total flavonoid content enhanced plant salinity tolerance, implying the importance of AvFLS gene responses to salinity stress.

Histone Deacetylase Inhibitor SAHA Improves High Salinity Tolerance Associated with Hyperacetylation-Enhancing Expression of Ion Homeostasis-Related Genes in Cotton

Histone acetylation plays an important role in regulation of chromatin structure and gene expression in terms of responding to abiotic stresses. Histone acetylation is modulated by histone deacetylases (HDACs) and histone acetyltransferases. Recently, the effectiveness of HDAC inhibitors (HDACis) for conferring plant salt tolerance has been reported. However, the role of HDACis in cotton has not been elucidated. In the present study, we assessed the effects of the HDACi suberoylanilide hydroxamic acid (SAHA) during high salinity stress in cotton. We demonstrated that 10 μM SAHA pretreatment could rescue of cotton from 250 mM NaCl stress, accompanied with reduced Na+ accumulation and a strong expression of the ion homeostasis-related genes. Western blotting and immunostaining results revealed that SAHA pretreatment could induce global hyperacetylation of histone H3 at lysine 9 (H3K9) and histone H4 at lysine 5 (H4K5) under 250 mM NaCl stress, indicating that SAHA could act as the HDACi in cotton. Chromatin immunoprecipitation and chromatin accessibility coupled with real time quantitative PCR analyses showed that the upregulation of the ion homeostasis-related genes was associated with the elevated acetylation levels of H3K9 and H4K5 and increased chromatin accessibility on the promoter regions of these genes. Our results could provide a theoretical basis for analyzing the mechanism of HDACi application on salt tolerance in plants.