NaCl-induced expression of AtVHA-c5 gene in the roots plays a role in response of Arabidopsis to salt stress

A Plate Growth Assay to Quantify Embryonic Root Development of Zea mays

Murashige-Skoog medium solutions have been used in a variety of plant plate growth assays, yet most research uses Arabidopsis thaliana as the study organism. For larger seeds such as maize (Zea mays), most protocols employ a paper towel roll method for experiments, which often involves wrapping maize seedlings in wet, sterile germination paper. What the paper towel roll method lacks, however, is the ability to image the roots over time without risk of contamination. Here, we describe a sterile plate growth assay that contains Murashige-Skoog medium to grow seedlings starting two days after germination. This protocol uses a section of a paper towel roll method to achieve uniform germination of maize seedlings, which are sterilely transferred onto large acrylic plates for the duration of the experiment. The media can undergo modification to include an assortment of plant hormones, exogenous sugars, and other chemicals. The acrylic plates allow researchers to freely image the plate without disturbing the seedlings and control the environment in which the seedlings are grown, such as modifications in temperature and light. Additionally, the protocol is widely adaptable for use with other cereal crops. Key features • Builds upon plate growth methods routinely used for Arabidopsis seedlings but that are inadequate for maize. • Real-time photographic analysis of seedlings up to two weeks following germination. • Allows for testing of various growth conditions involving an assortment of additives and/or modification of environmental conditions. • Samples are able to be collected for genotype screening.

Exogenous hydrogen sulfide mediates Na+ and K+ fluxes of salt gland in salt-secreting mangrove plant Avicennia marina

Hydrogen sulfide (H2S), is a crucial biological player in plants. Here, we primarily explored the interaction between sodium hydrosulfide (NaHS, a H2S donor) and the fluxes of Na+ and K+ from the salt glands of mangrove species Avicennia marina (Forsk.) Vierh. with non-invasive micro-test technology (NMT) and quantitative real-time PCR (qRT-PCR) approaches under salinity treatments. The results showed that under 400-mM NaCl treatment, the addition of 200-μM NaHS markedly increased the quantity of salt crystals in the adaxial epidermis of A. marina leaves, accompanied by an increase in the K+/Na+ ratio. Meanwhile, the endogenous content of H2S was dramatically elevated in this process. The NMT result revealed that the Na+ efflux was increased from salt glands, whereas K+ efflux was decreased with NaHS application. On the contrary, the effects of NaHS were reversed by H2S scavenger hypotaurine (HT), and DL-propargylglycine (PAG), an inhibitor of cystathionine-γ-lyase (CES, a H2S synthase). Moreover, enzymic assay revealed that NaHS increased the activities of plasma membrane and tonoplast H+-ATPase. qRT-PCR analysis revealed that NaHS significantly increased the genes transcript levels of tonoplast Na+/H+ antiporter (NHX1), plasma membrane Na+/H+ antiporter (SOS1), plasma membrane H+-ATPase (AHA1) and tonoplast H+-ATPase subunit c (VHA-c1), while suppressed above-mentioned gene expressions by the application of HT and PAG. Overall, H2S promotes Na+ secretion from the salt glands of A. marina by up-regulating the plasma membrane and tonoplast Na+/H+ antiporter and H+-ATPase.

The Plant V-ATPase

V-ATPase is the dominant proton pump in plant cells. It contributes to cytosolic pH homeostasis and energizes transport processes across endomembranes of the secretory pathway. Its localization in the trans Golgi network/early endosomes is essential for vesicle transport, for instance for the delivery of cell wall components. Furthermore, it is crucial for response to abiotic and biotic stresses. The V-ATPase's rather complex structure and multiple subunit isoforms enable high structural flexibility with respect to requirements for different organs, developmental stages, and organelles. This complexity further demands a sophisticated assembly machinery and transport routes in cells, a process that is still not fully understood. Regulation of V-ATPase is a target of phosphorylation and redox-modifications but also involves interactions with regulatory proteins like 14-3-3 proteins and the lipid environment. Regulation by reversible assembly, as reported for yeast and the mammalian enzyme, has not be proven in plants but seems to be absent in autotrophic cells. Addressing the regulation of V-ATPase is a promising approach to adjust its activity for improved stress resistance or higher crop yield.

Current progress in plant V-ATPase: From biochemical properties to physiological functions

Vacuolar-type adenosine triphosphatase (V-ATPase, VHA) is a highly conserved, ATP-driven multisubunit proton pump that is widely distributed in all eukaryotic cells. V-ATPase consists of two domains formed by at least 13 different subunits, the membrane peripheral V₁ domain responsible for ATP hydrolysis, and the membrane-integral V₀ domain responsible for proton translocation. V-ATPase plays an essential role in energizing secondary active transport and is indispensable to plants. In addition to multiple stress responses, plant V-ATPase is also implicated in physiological processes such as growth, development, and morphogenesis. Based on the identification of distinct V-ATPase mutants and advances in luminal pH measurements in vivo, it has been revealed that this holoenzyme complex plays a pivotal role in pH homeostasis of the plant endomembrane system and endocytic and secretory trafficking. Here, we review recent progress in comprehending the biochemical properties and physiological functions of plant V-ATPase and explore the topics that require further elucidation.

Genome-Wide Identification of the Vacuolar H+-ATPase Gene Family in Five Rosaceae Species and Expression Analysis in Pear (Pyrus bretschneideri)

Vacuolar H⁺-ATPases (V-ATPase) are multi-subunit complexes that function as ATP hydrolysis-driven proton pumps. They play pivotal roles in physiological processes, such as development, metabolism, stress, and growth. However, there have been very few studies on the characterisation of V-ATPase (VHA) genes in Rosaceae species. Therefore, in the present study, we performed a genome-wide analysis and identified VHA gene family members in five Rosaceae species (Pyrus bretschneideri, Malus domestica, Prunus persica, Fragaria vesca, and Prunus mume). A total of 159 VHA genes were identified, and were classified into 13 subfamilies according to the phylogenetic analysis. The structure of VHA proteins revealed high similarity among different VHA genes within the same subgroup. Gene duplication event analysis revealed that whole-genome duplications represented the major pathway for expansion of the Pyrus bretschneideri VHA genes (PbrVHA genes). The tissue-specific expression analysis of the pear showed that 36 PbrVHA genes were expressed in major tissues. Seven PbrVHA genes were significantly downregulated when the pollen tube growth stopped. Moreover, many PbrVHA genes were differentially expressed during fruit development and storage, suggesting that VHA genes play specific roles in development and senescence. The present study provides fundamental information for further elucidating the potential roles of VHA genes during development and senescence.

Morphological and physiological responses of two willow species from different habitats to salt stress

Plant salt tolerance is a complex mechanism, and different plant species have different strategies for surviving salt stress. In the present study, we analyzed and compared the morphological and physiological responses of two willow species (Salix linearistipularis and Salix matsudana) from different habitats to salt stress. S. linearistipularis exhibited higher seed germination rates and seedling root Na⁺ efflux than S. matsudana under salt stress. After salt treatment, S. linearistipularis leaves exhibited less Na⁺ accumulation, loss of water and chlorophyll, reduction in photosynthetic capacity, and damage to leaf cell structure than leaves of S. matsudana. Scanning electron microscopy combined with gas chromatography mass spectrometry showed that S. linearistipularis leaves had higher cuticular wax loads than S. matsudana leaves. Overall, our results showed that S. linearistipularis had higher salt tolerance than S. matsudana, which was associated with different morphological and physiological responses to salt stress. Furthermore, our study suggested that S. linearistipularis could be a promising tree species for saline-alkali land greening and improvement.

Sexual Differences in Physiological and Transcriptional Responses to Salinity Stress of Salix linearistipularis

Willow (Salix), a dioecious plant, is an important ornamental tree species in the world. Salix linearistipularis, a perennial woody plant species naturally distributed on the Songnen Plain saline-alkali land in northeast China, has a high saline condition. To study the sexual differences of S. linearistipularis in salinity tolerance, the physiological and transcriptional responses to salinity were compared between female and male cuttings. Under salinity stress, the female leaves exhibited higher superoxide dismutase and peroxidase activities and photosynthetic capacity, and lower H2O2 contents than those of male leaves. Under salinity stress, sodium (Na+) accumulation in female leaves was lower than that in the male leaves. The non-invasive micro-test showed that the net Na+ efflux in the salt-treated female roots was higher than that in male roots. Physiological responses revealed that female cuttings were more tolerant than males, which may be mainly due to females having lower leaf Na+ accumulation and higher root Na+ efflux capacity than males. Transcriptional analyses showed that 108 differentially expressed salt-responsive genes were identified in both female and male roots; most of these showed sexual differences in expression patterns under salinity stress. RNA-seq combined with qPCR analysis showed that the salt-induced expression of four Na+/H+ antiporter (NHX) genes (SlNHX3, 5, 6, 7) in female roots was higher than that in male roots. Transcriptional analyses revealed that the higher Na+ efflux capacity in female roots than in male roots may be closely related to the differential expression of salt-responsive genes, especially NHX genes.

Bacillus amyloliquefaciens PDR1 from root of karst adaptive plant enhances Arabidopsis thaliana resistance to alkaline stress through modulation of plasma membrane H+-ATPase activity

Exploration of native microbes is a feasible way to develop microbial agents for ecological restoration. This study was aimed to explore the impact of Bacillus amyloliquefaciens PDR1 from karst adaptive plant on the activity of root plasma membrane H⁺-ATPase in Arabidopsis thaliana. A. thaliana was cultured in presence or absence of B. amyloliquefaciens PDR1 and its effects on the growth were evaluated by measuring the taproot length and dry weight. The rhizosphere acidification capacity was detected by a pH indicator, a pH meter and non-invasive micro-test techniques (NMT). The nutrient uptake was performed using appropriate methods. A combination of transcriptome sequencing and real-time quantitative polymerase chain reaction (qRT-PCR) was used to measure the expression of functional genes that regulate the plasma membrane H⁺-ATPase activity in A. thaliana roots. Functional analysis was performed to understand how B. amyloliquefaciens regulates biological processes and metabolic pathways to strengthen A. thaliana resistance to alkaline stress. Here, we show that volatile organic compounds (VOCs) from B. amyloliquefaciens PDR1 promoted the growth and development of A. thaliana, enhanced the plasma membrane H⁺-ATPase activity, and affected ion absorption in Arabidopsis roots. Moreover, B. amyloliquefaciens PDR1 VOCs did not affect the expression of the gene coding for plasma membrane H⁺-ATPase, but affected the expression of genes regulating the activity of plasma membrane H⁺-ATPase. Our findings illuminate the mechanism by which B. amyloliquefaciens regulates the growth and alkaline stress resistance of A. thaliana, and lay a foundation for wide and efficient application for agricultural production and ecological protection.

Arabidopsis V-ATPase d2 Subunit Plays a Role in Plant Responses to Oxidative Stress

Vacuolar-type H⁺-ATPase (V-ATPase), a multisubunit proton pump located on the endomembrane, plays an important role in plant growth. The Arabidopsis thaliana V-ATPase d subunit (VHA-d) consists of two isoforms; AtVHA-d1 and AtVHA-d2. In this study, the function of AtVHA-d2 was investigated. Histochemical analysis revealed that the expression of AtVHA-d1 and AtVHA-d2 was generally highly overlapping in multiple tissues at different developmental stages of Arabidopsis. Subcellular localization revealed that AtVHA-d2 was mainly localized to the vacuole. AtVHA-d2 expression was significantly induced by oxidative stress. Analysis of phenotypic and H₂O₂ content showed that the atvha-d2 mutant was sensitive to oxidative stress. The noninvasive microtest monitoring demonstrated that the net H⁺ influx in the atvha-d2 roots was weaker than that in the wild-type under normal conditions. However, oxidative stress resulted in the H⁺ efflux in atvha-d2 roots, which was significantly different from that in the wild-type. RNA-seq combined with qPCR analysis showed that the expression of several members of the plasma membrane H⁺-ATPase gene (AtAHA) family in atvha-d2 was significantly different from that in the wild-type. Overall, our results indicate that AtVHA-d2 plays a role in Arabidopsis in response to oxidative stress by affecting H⁺ flux and AtAHA gene expression.

PsCor413pm2, a Plasma Membrane-Localized, Cold-Regulated Protein from Phlox subulata, Confers Low Temperature Tolerance in Arabidopsis

Low temperature stress adversely affects plant growth and development. Isolation and characterization of cold response genes from cold-tolerant plants help to understand the mechanism underlying low temperature tolerance. In this study, PsCor413pm2, a cold-regulated (COR) gene isolated from Phlox subulata, was transferred to Arabidopsis plants to investigate its function. Real-time quantitative PCR analysis revealed that PsCor413pm2 expression was induced by cold. Subcellular localization revealed that the PsCor413pm2-green fluorescent protein (GFP) fusion protein localized to the plasma membrane in tobacco and Arabidopsis plants. Furthermore, overexpression of PsCor413pm2 in Arabidopsis plants enhanced tolerance to low temperature stress. Transgenic Arabidopsis roots had more influx of Ca²⁺ after a cold shock than wild-type plants, as shown using non-invasive micro-test technology (NMT). Moreover, the transcription abundance of five COR and two C-repeat (CRT) binding factor (CBF) genes in transgenic Arabidopsis plants was higher than that in the wild-type plants under cold stress. Taken together, our results suggest that overexpression of PsCor413pm2 enhances low temperature tolerance in Arabidopsis plants by affecting Ca²⁺ flux and the expression of stress-related COR and CBF genes.

DsSWEET17, a Tonoplast-Localized Sugar Transporter from Dianthus spiculifolius, Affects Sugar Metabolism and Confers Multiple Stress Tolerance in Arabidopsis

Plant SWEETs (Sugars Will Eventually be Exported Transporters) affect the growth of plants by regulating the transport of sugar from source to sink and its intracellular transport between different organelles. In this study, DsSWEET17 from Dianthus spiculifolius was identified and characterized. Real-time quantitative PCR analysis revealed that the expression of DsSWEET17 was affected by exogenous application of fructose and glucose as well as under salt, osmotic, and oxidation stress. Colocalization experiments showed that the DsSWEET17-GFP (green fluorescent protein) fusion protein was localized to the FM4-64-labeled tonoplasts in Arabidopsis. Compared to the wild type, the transgenic Arabidopsis seedlings overexpressing DsSWEET17 had longer roots, greater fresh weight, and a faster root growth upon exogenous application of fructose. Furthermore, transgenic Arabidopsis seedlings had significantly higher fructose accumulation than was observed for the wild-type seedlings. The analysis of root length revealed that transgenic Arabidopsis had higher tolerance to salt, osmotic, and oxidative stresses. Taken together, our results suggest that DsSWEET17 may be a tonoplast sugar transporter, and its overexpression affects sugar metabolism and confers multiple stress tolerance in Arabidopsis.