Strigolactones alleviate AlCl3 stress by vacuolar compartmentalization and cell wall blocking in apple.

Poor management and excess fertilization of apple (Malus domestica Borkh.) orchards are causing increasingly serious soil acidification, resulting in Al toxicity and direct poisoning of roots. Strigolactones (SLs) are reported to be involved in plant responses to abiotic stress, but their role and mechanism under AlCl3 stress remain unknown. Here, we found that applying 1 µm GR24 (an SL analoge) significantly alleviated AlCl3 stress of M26 apple rootstock, mainly by blocking the movement of Al through cell wall and by vacuolar compartmentalization of Al. RNA-seq analysis identified the core transcription factor gene MdWRKY53, and overexpressing MdWRKY53 enhanced AlCl3 tolerance in transgenic apple plants through the same mechanism as GR24. Subsequently, we identified MdPMEI45 (encoding pectin methylesterase inhibitor) and MdALS3 (encoding an Al transporter) as downstream target genes of MdWRKY53 using chromatin immunoprecipitation followed by sequencing (ChIP-seq). GR24 enhanced the interaction between MdWRKY53 and the transcription factor MdTCP15, further increasing the binding of MdWRKY53 to the MdPMEI45 promoter and inducing MdPMEI45 expression to prevent Al from crossing cell wall. MdWRKY53 also bound to the promoter of MdALS3 and enhanced its transcription to compartmentalize Al in vacuoles under AlCl3 stress. We therefore identified two modules involved in alleviating AlCl3 stress in woody plant apple: the SL-WRKY+TCP-PMEI module required for excluding external Al by blocking the entry of Al3+ into cells and the SL-WRKY-ALS module allowing internal detoxification of Al through vacuolar compartmentalization. These findings lay a foundation for the practical application of SLs in agriculture.

Systematic Investigation of Aluminum Stress-Related Genes and Their Critical Roles in Plants.

Aluminum (Al) stress is a dominant obstacle for plant growth in acidic soil, which accounts for approximately 40-50% of the world's potential arable land. The identification and characterization of Al stress response (Al-SR) genes in Arabidopsis, rice, and other plants have deepened our understanding of Al's molecular mechanisms. However, as a crop sensitive to acidic soil, only eight Al-SR genes have been identified and functionally characterized in maize. In this review, we summarize the Al-SR genes in plants, including their classifications, subcellular localizations, expression organs, functions, and primarily molecular regulatory networks. Moreover, we predict 166 putative Al-SR genes in maize based on orthologue analyses, facilitating a comprehensive understanding of the impact of Al stress on maize growth and development. Finally, we highlight the potential applications of alleviating Al toxicity in crop production. This review deepens our understanding of the Al response in plants and provides a blueprint for alleviating Al toxicity in crop production.

Nitrate improves aluminium resistance through SLAH-mediated citrate exudation from roots.

Aluminium (Al) toxicity is one of the major constraint for crop production in acidic soil, and the inappropriate utilization of nitrogen fertilizer can accelerate soil acidification. Despite previous studies investigating the regulation of nitrogen forms in Al toxicity of plants, the underlying mechanism, particularly at the molecular level, remains unclear. This study aims to uncover the potentially regulatory mechanism of nitrate (NO3 - ) in the Al resistance of maize and Arabidopsis. NO3 - conservatively improves Al resistance in maize and Arabidopsis, with nitrate-elevated citrate synthesis and exudation potentially playing critical roles in excluding Al from the root symplast. ZmSLAH2 in maize and AtSLAH1 in Arabidopsis are essential for the regulation of citrate exudation and NO3 - -promoted Al resistance, with ZmMYB81 directly targeting the ZmSLAH2 promoter to activate its activity. Additionally, NO3 - transport is necessary for NO3 - -promoted Al resistance, with ZmNRT1.1A and AtNRT1.1 potentially playing vital roles. The suppression of NO3 - transport in roots by ammonium (NH4 + ) may inhibit NO3 - -promoted Al resistance. This study provides novel insights into the understanding of the crucial role of NO3 - -mediated signalling in the Al resistance of plants and offers guidance for nitrogen fertilization on acid soils.

Two Sweet Sorghum (Sorghum bicolor L.) WRKY Transcription Factors Promote Aluminum Tolerance via the Reduction in Callose Deposition.

Aluminum (Al) toxicity is a primary limiting factor for crop production in acidic soils. The WRKY transcription factors play important roles in regulating plant growth and stress resistance. In this study, we identified and characterized two WRKY transcription factors, SbWRKY22 and SbWRKY65, in sweet sorghum (Sorghum bicolor L.). Al induced the transcription of SbWRKY22 and SbWRKY65 in the root apices of sweet sorghum. These two WRKY proteins were localized in the nucleus and exhibited transcriptional activity. SbWRKY22 showed the significant transcriptional regulation of SbMATE, SbGlu1, SbSTAR1, SbSTAR2a, and SbSTAR2b, which are major known Al tolerance genes in sorghum. Interestingly, SbWRKY65 had almost no effect on the aforementioned genes, but it significantly regulated the transcription of SbWRKY22. Therefore, it is speculated that SbWRKY65 might indirectly regulate Al-tolerance genes mediated by SbWRKY22. The heterologous expression of SbWRKY22 and SbWRKY65 greatly improved the Al tolerance of transgenic plants. The enhanced Al tolerance phenotype of transgenic plants is associated with reduced callose deposition in their roots. These findings suggest the existence of SbWRKY22- and SbWRKY65-mediated Al tolerance regulation pathways in sweet sorghum. This study extends our understanding of the complex regulatory mechanisms of WRKY transcription factors in response to Al toxicity.

Physiological and Transcriptomic Analysis Reveals That Melatonin Alleviates Aluminum Toxicity in Alfalfa (Medicago sativa L.).

Aluminum (Al) toxicity is the most common factor limiting the growth of alfalfa in acidic soil conditions. Melatonin (MT), a significant pleiotropic molecule present in both plants and animals, has shown promise in mitigating Al toxicity in various plant species. This study aims to elucidate the underlying mechanism by which melatonin alleviates Al toxicity in alfalfa through a combined physiological and transcriptomic analysis. The results reveal that the addition of 5 µM melatonin significantly increased alfalfa root length by 48% and fresh weight by 45.4% compared to aluminum treatment alone. Moreover, the 5 µM melatonin application partially restored the enlarged and irregular cell shape induced by aluminum treatment, resulting in a relatively compact arrangement of alfalfa root cells. Moreover, MT application reduces Al accumulation in alfalfa roots and shoots by 28.6% and 27.6%, respectively. Additionally, MT plays a crucial role in scavenging Al-induced excess H2O2 by enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), consequently reducing malondialdehyde (MDA) levels. More interestingly, the RNA-seq results reveal that MT application significantly upregulates the expression of xyloglucan endotransglucosylase/hydrolase (XTH) and carbon metabolism-related genes, including those involved in the glycolysis process, as well as sucrose and starch metabolism, suggesting that MT application may mitigate Al toxicity by facilitating the binding of Al to the cell walls, thereby reducing intracellular Al accumulation, and improving respiration and the content of sucrose and trehalose. Taken together, our study demonstrates that MT alleviates Al toxicity in alfalfa by reducing Al accumulation and restoring redox homeostasis. These RNA-seq results suggest that the alleviation of Al toxicity by MT may occur through its influence on cell wall composition and carbon metabolism. This research advances our understanding of the mechanisms underlying MT's effectiveness in mitigating Al toxicity, providing a clear direction for our future investigations into the underlying mechanisms by which MT alleviates Al toxicity in alfalfa.

Aluminum uptake, translocation, physiological changes, and overall growth inhibition in rice genotypes (Oryza sativa) at vegetative stage.

Aluminum (Al) contamination in acidic soil is a major problem in paddy field, causing grain yield loss, especially in central plains of Thailand. The objective of this study was to assess Al content in the root tissues, its translocation to the leaves, and Al toxicity in three genotypes of rice, RD35 (local acidic-tolerant), Azucena (positive-check Al-tolerant), and IR64 (high yielding) under 0 (control) or 1 mM AlCl3 (Al toxicity) at pH 4.5. Al content in the root tissues of rice cv. RD35 under 1 mM AlCl3 was peaked at 4.18 mg g‒1 DW and significantly translocated to leaf tissues (0.35 mg g‒1 DW), leading to reduced leaf greenness (SPAD) (by 44.9% over the control) and declined net photosynthetic rate (Pn) (by 54.5% over the control). In contrast, Al level in cvs. Azucena and IR64 was restricted in the roots (2.12 mg g‒1 DW) with low amount of translocation in the leaf tissues (0.26 mg g‒1 DW), resulting in maintained values of SPAD and Pn. In cv. RD35, root and shoot traits including root length, root fresh weight, shoot height, shoot fresh weight, and shoot dry weight in 1 mM Al treatment were significantly dropped by > 35% over the control, whereas these parameters in cvs. Azucena and IR64 were retained. Based on the results, RD35 rice genotype was identified as Al sensitive as it demonstrated Al toxicity in both aboveground and belowground parts, whereas Azucena and IR64 were found tolerant to 1 mM Al as they demonstrated storage of Al in the root tissues to reduce toxicity in the leaf tissues. The study suggests that root traits, shoot attributes, chlorophyll degradation, and photosynthetic reduction can be successfully employed for the screening of Al-tolerant genotypes in rice breeding programs.

The aluminum distribution and translocation in two citrus species differing in aluminum tolerance.

BACKGROUND: Many citrus orchards of south China suffer from soil acidification, which induces aluminum (Al) toxicity. The Al-immobilization in vivo is crucial for Al detoxification. However, the distribution and translocation of excess Al in citrus species are not well understood. RESULTS: The seedlings of 'Xuegan' [Citrus sinensis (L.) Osbeck] and 'Shatianyou' [Citrus grandis (L.) Osbeck], that differ in Al tolerance, were hydroponically treated with a nutrient solution (Control) or supplemented by 1.0 mM Al3+ (Al toxicity) for 21 days after three months of pre-culture. The Al distribution at the tissue level of citrus species followed the order: lateral roots > primary roots > leaves > stems. The concentration of Al extracted from the cell wall (CW) of lateral roots was found to be about 8 to 10 times higher than in the lateral roots under Al toxicity, suggesting that the CW was the primary Al-binding site at the subcellular level. Furthermore, the Al distribution in CW components of the lateral roots showed that pectin had the highest affinity for binding Al. The relative expression level of genes directly relevant to Al transport indicated a dominant role of Cs6g03670.1 and Cg1g021320.1 in the Al distribution of two citrus species. Compared to C. grandis, C. sinensis had a significantly higher Al concentration on the CW of lateral roots, whereas remarkably lower Al levels in the leaves and stems. Furthermore, Al translocation revealed by the absorption kinetics of the CW demonstrated that C. sinensis had a higher Al retention and stronger Al affinity on the root CW than C. grandis. According to the FTIR (Fourier transform infrared spectroscopy) analysis, the Al distribution and translocation might be affected by a modification in the structure and components of the citrus lateral root CW. CONCLUSIONS: A higher Al-retention, mainly attributable to pectin of the root CW, and a lower Al translocation efficiency from roots to shoots contributed to a higher Al tolerance of C. sinensis than C. grandis. The aluminum distribution and translocation of two citrus species differing in aluminum tolerance were associated with the transcriptional regulation of genes related to Al transport and the structural modification of root CW.

ZmNRAMP4 Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana.

Aluminum (Al) toxicity causes severe reduction in crop yields in acidic soil. The natural resistance-associated macrophage proteins (NRAMPs) play an important role in the transport of mineral elements in plants. Recently, OsNrat1 and SbNrat1 were reported specifically to transport trivalent Al ions. In this study, we functionally characterized ZmNRAMP4, a gene previously identified from RNA-Seq data from Al-treated maize roots, in response to Al exposure in maize. ZmNRAMP4 was predominantly expressed in root tips and was specifically induced by Al stress. Yeast cells expressing ZmNRAMP4 were hypersensitive to Al, which was associated with Al accumulation in yeast. Furthermore, overexpression of ZmNRAMP4 in Arabidopsis conferred transgenic plants with a significant increase in Al tolerance. However, expression of ZmNRAMP4, either in yeast or in Arabidopsis, had no effect on the response to cadmium stress. Taken together, these results underlined an internal tolerance mechanism involving ZmNRAMP4 to enhance Al tolerance via cytoplasmic sequestration of Al in maize.

Overexpression of the Aldehyde Dehydrogenase Gene ZmALDH Confers Aluminum Tolerance in Arabidopsis thaliana.

Aluminum (Al) toxicity is the main factor limiting plant growth and the yield of cereal crops in acidic soils. Al-induced oxidative stress could lead to the excessive accumulation of reactive oxygen species (ROS) and aldehydes in plants. Aldehyde dehydrogenase (ALDH) genes, which play an important role in detoxification of aldehydes when exposed to abiotic stress, have been identified in most species. However, little is known about the function of this gene family in the response to Al stress. Here, we identified an ALDH gene in maize, ZmALDH, involved in protection against Al-induced oxidative stress. Al stress up-regulated ZmALDH expression in both the roots and leaves. The expression of ZmALDH only responded to Al toxicity but not to other stresses including low pH and other metals. The heterologous overexpression of ZmALDH in Arabidopsis increased Al tolerance by promoting the ascorbate-glutathione cycle, increasing the transcript levels of antioxidant enzyme genes as well as the activities of their products, reducing MDA, and increasing free proline synthesis. The overexpression of ZmALDH also reduced Al accumulation in roots. Taken together, these findings suggest that ZmALDH participates in Al-induced oxidative stress and Al accumulation in roots, conferring Al tolerance in transgenic Arabidopsis.

Method for initially selecting Al-tolerant rice varieties based on the charge characteristics of their roots.

To explore the relationship between charge characteristics of rice roots and aluminum (Al) tolerance of rice, roots of 47 different rice genotypes were obtained by hydroponic experiment. The zeta potentials of roots were determined by streaming potential method, and the Al tolerance and the functional groups of rice were measured by relative root elongation and infrared spectroscopy (ATR-FTIR), respectively. The exchangeable, complexed and precipitated Al(III) sorbed on the root surface of rice was extracted with 1 mol L-1 KNO3, 0.05 mol L-1 EDTA-2Na and 0.01 mol L-1 HCl, respectively. There was a significant correlation between the zeta potentials and the relative elongation of rice roots, indicating that the zeta potentials of rice roots could be used to characterize rice tolerance to Al toxicity. Twelve Al-tolerant rice varieties, 25 medium Al-tolerant rice varieties, and 10 Al-sensitive rice varieties were obtained. The Al-tolerant rice varieties sorbed less complexed Al(III) and total Al(III) because there was lower negative charge on their roots compared to less tolerant genotypes. A correlation analysis showed that there were significant negative correlations between the zeta potential, relative root elongation, and the total Al(III) sorption capacity of the roots, which further confirmed the reliability of using the root zeta potential to characterize rice tolerance to Al toxicity. The results of this paper provide a new method for screening Al-tolerant rice varieties.

Showing their mettle: extraradical mycelia of arbuscular mycorrhizae form a metal filter to improve host Al tolerance and P nutrition.

BACKGROUND: New evidence has shown that arbuscular mycorrhizal (AM) fungi can contribute to the aluminum (Al3+ ) tolerance of host plants growing in acidic soils with phytotoxic levels of Al3+ . The aim of this study was to investigate the role of AM fungi isolated from naturally occurring Al3+ acidic soils in conferring host tolerance to Al3+ toxicity in three wheat cultivars differing in Al3+ sensitivity. The experiment was conducted in a soilless substrate (vermiculite/perlite, 2:1 v/v) using two Al3+ -tolerant wheat genotypes and one Al3+ -sensitive wheat genotype. The wheat was colonized with a consortium of AM fungi isolated from an Andisol, with or without Al3+ at a concentration of 200 µmol L-1 . RESULTS: The response of wheat to Al3+ in the medium was dependent on both the plant genotype and AM colonization. The benefits of the AM fungi to the wheat cultivars included an increased P concentration and relatively low Al3+ accumulation in the plants. This was achieved through two mechanisms. First, the metal-chelating capacity of the AM fungi was clear in two of the cultivars ('Tukan' and 'Porfiado'), in which the enhanced extraradical mycelium development was able to retain Al3+ in the glomalin and hyphae. Second, the increased AM-induced acid phosphatase activity in the rhizosphere of the other cultivar ('Atlas 66') increased host nutrition possibly by hyphae-mediated nutrient uptake and glomalin-related soil protein. CONCLUSION: The results suggest that the role of AM fungi in cultivar-specific Al3+ detoxification can be achieved by increased extraradical mycelial filters and enhanced bioavailability of P in the host rhizosphere. © 2019 Society of Chemical Industry.

Molecular Mechanisms for Coping with Al Toxicity in Plants.

Aluminum (Al) toxicity is one of the major constraints to agricultural production in acid soils. Molecular mechanisms of coping with Al toxicity have now been investigated in a range of plant species. Two main mechanisms of Al tolerance in plants are Al exclusion from the roots and the ability to tolerate Al in the roots. This review focuses on the recent discovery of novel genes and mechanisms that confer Al tolerance in plants and summarizes our understanding of the physiological, genetic, and molecular basis for plant Al tolerance. We hope this review will provide a theoretical basis for the genetic improvement of Al tolerance in plants.

Boron reduces aluminum-induced growth inhibition, oxidative damage and alterations in the cell wall components in the roots of trifoliate orange.

Aluminum (Al) toxicity is a major restriction for crops production on acidic soils. The primary symptom of aluminum toxicity is visible in the roots of plants. Recently, several studies reported the alleviation of Al toxicity by the application of Boron (B), however, the information how B alleviates Al toxicity is not well understood. Thus, we investigated the ameliorative response of B on Al-induced growth inhibition, oxidative damages, and variations in the cell wall components in trifoliate orange roots. The results indicated that plants under Al stress experienced a substantial decrement in root length and overall plant growth. The supply of B improved the root elongation by eliminating oxidative stress, membrane peroxidation, membrane leakage, and cell death produced under Al toxicity. Moreover, accumulation of Al on the cell wall and alteration in the cell wall components might be one of the causes resulting in the quick inhibition of root elongation under B-starvation circumstances by providing susceptible negative charges on pectin matrix for binding of Al. The results provide a useful understanding of the insight into mechanisms of B-induced mitigation of Al toxicity especially in the trifoliate orange that might be helpful in the production of crops on acidic soils.

Methane enhances aluminum resistance in alfalfa seedlings by reducing aluminum accumulation and reestablishing redox homeostasis.

Methane (CH4) is emerging as a candidate of signal molecule recently. However, whether or how CH4 enhances plant adaptation to aluminum (Al)-contaminated environment is still unknown. In this report, the physiological roles and possible molecular mechanisms of CH4 in the modulation of Al toxicity in alfalfa seedlings were characterized. Our results showed that, CH4 pretreatment could alleviate Al-induced seedling growth inhibition and redox imbalance. The defensive effects of CH4 against Al toxicity including the remission of Al-induced root elongation inhibition, nutrient disorder, and relative electrolyte leakage. Moreover, contents of organic acids, including citrate, malate, and oxalate, were increased by CH4. These results were paralleled by the findings of CH4 regulated organic acids metabolism and transport genes, citrate synthase, malate dehydrogenase, aluminum-activated malate transporter, and aluminum activated citrate transporter. Consistently, Al accumulation in seedling roots was decreased after CH4 treatment. In addition, Al-induced oxidative stress was also alleviated by CH4, through the regulation of the activities of anti-oxidative enzymes, such as ascorbate peroxidase, superoxide dismutase, and peroxidase, as well as their corresponding transcripts. Our data clearly suggested that CH4 alleviates Al toxicity by reducing Al accumulation in organic acid-dependent fashion, and reestablishing redox homeostasis.

Linking hydrogen-enhanced rice aluminum tolerance with the reestablishment of GA/ABA balance and miRNA-modulated gene expression: A case study on germination.

Although previous results showed that exogenous hydrogen (H2) alleviated aluminum (Al) toxicity, the detailed mechanism remains unclear. Here, we reported that the exposure of germinating rice seeds to Al triggered H2 production, followed by a decrease of GA/ABA ratio and seed germination inhibition. Compared to inert gas (argon), H2 pretreatment not only strengthened H2 production and alleviated Al-induced germination inhibition, but also partially reestablished the balance between GA and ABA. By contrast, a GA biosynthesis inhibitor paclobutrazol (PAC) could block the H2-alleviated germination inhibition. The expression of GA biosynthesis genes (GA20ox1 and GA20ox2) and ABA catabolism genes (ABA8ox1 and ABA8ox2), was also induced by H2. Above results indicated that GA/ABA might be partially involved in H2 responses. Subsequent results revealed that compared with Al alone, transcripts of miR398a and miR159a were decreased by H2, and expression levels of their target genes OsSOD2 and OsGAMYB were up-regulated. Whereas, miR528 and miR160a transcripts were increased differentially, and contrasting tendencies were observed in the changes of their target genes (OsAO and OsARF10). The transcripts of Al-tolerant gene OsSTAR1/OsSTAR2 and OsFRDL4 were up-regulated. Above results were consistent with the anti-oxidant defense, decreased Al accumulation, and enhanced citrate efflux. Together, our results provided insight into the mechanism underlying H2-triggered Al tolerance in plants.

Phytohormone regulation of root growth triggered by P deficiency or Al toxicity.

Phosphorus (P) deficiency and aluminum (Al) toxicity often coexist and limit plant growth on acid soils. It has been well documented that both P deficiency and Al toxicity alter root growth, including inhibition of primary roots and promotion of lateral roots. This suggests that plants adapt to both stresses through a common regulation pathway. Although an expanding set of results shows that phytohormones play vital roles in controlling root responses to Pi starvation and Al toxicity, it remains largely unknown whether P and Al coordinately regulate root growth through interacting phytohormone biosynthesis and signal transduction pathways. This review provides a summary of recent results concerning the influences of P deficiency and Al toxicity on root growth through the action of phytohormones, most notably auxin and ethylene. The objective is to facilitate increasing insights into complex responses of plants to adverse factors common on acid soils, which can spur development of 'smart' cultivars with better root growth and higher yield on these globally distributed marginal soils.

Aluminum toxicity risk reduction as a result of reduced acid deposition in Adirondack lakes and ponds.

In 1990, the US Congress amended the Clean Air Act (CAA) to reduce regional-scale ecosystem degradation from SO x and NO x emissions which have been responsible for acid deposition in regions such as the Adirondack Mountains of New York State. An ecosystem assessment project was conducted from 1994 to 2012 by the Darrin Fresh Water Institute to determine the effect of these emission reduction policies on aquatic systems. The project investigated water chemistry and biota in 30 Adirondack lakes and ponded waters. Although regulatory changes made in response to the 1990 CAA amendments resulted in a reduction of acid deposition within the Adirondacks, the ecosystem response to these reductions is complicated. A statistical analysis of SO4, pH, Al, and DOC data collected during this project demonstrates positive change in response to decreased deposition. The changes in water chemistry also have lowered the risk of Al toxicity to brook trout (Salvelinus fontinalis [Mitchill]), which allowed the re-introduction of this species to Brooktrout Lake from which it had been extirpated. However, pH and labile aluminum (Alim) fluctuate and are not strongly correlated to changes in acid deposition. As such, toxicity to S. fontinalis also is cyclic and provides rationale for the difficulties inherent in re-establishing resident populations in impacted aquatic environments. Overall, aquatic ecosystems of the Adirondacks show a positive response to reduced deposition driven by changes in environmental policy, but the response is more complex and indicates an ecosystem-wide interaction between aquatic and watershed components of the ecosystem.

Phosphorylation and Interaction with the 14-3-3 Protein of the Plasma Membrane H+-ATPase are Involved in the Regulation of Magnesium-Mediated Increases in Aluminum-Induced Citrate Exudation in Broad Bean (Vicia faba. L).

Several studies have shown that external application of micromolar magnesium (Mg) can increase the resistance of legumes to aluminum (Al) stress by enhancing Al-induced citrate exudation. However, the exact mechanism underlying this regulation remains unknown. In this study, the physiological and molecular mechanisms by which Mg enhances Al-induced citrate exudation to alleviate Al toxicity were investigated in broad bean. Micromolar concentrations of Mg that alleviated Al toxicity paralleled the stimulation of Al-induced citrate exudation and increased the activity of the plasma membrane (PM) H(+)-ATPase. Northern blot analysis shows that a putative MATE-like gene (multidrug and toxic compound extrusion) was induced after treatment with Al for 4, 8 and 12 h, whereas the mRNA abundance of the MATE-like gene showed no significant difference between Al plus Mg and Al-only treatments during the entire treatment period. Real-time reverse transcription-PCR (RT-PCR) and Western blot analyses suggest that the transcription and translation of the PM H(+)-ATPase were induced by Al but not by Mg. In contrast, immunoprecipitation suggests that Mg enhanced the phosphorylation levels of VHA2 and its interaction with the vf14-3-3b protein under Al stress. Taken together, our results suggest that micromolar concentrations of Mg can alleviate the Al rhizotoxicity by increasing PM H(+)-ATPase activity and Al-induced citrate exudation in YD roots. This enhancement is likely to be attributable to Al-induced increases in the expression of the MATE-like gene and vha2 and Mg-induced changes in the phosphorylation levels of VHA2, thus changing its interaction with the vf14-3-3b protein.

Characterization of an inducible C2 H2 -type zinc finger transcription factor VuSTOP1 in rice bean (Vigna umbellata) reveals differential regulation between low pH and aluminum tolerance mechanisms.

The rice bean (Vigna umbellata) root apex specifically secretes citrate through expression activation of Vigna umbellata Multidrug and Toxic Compound Extrusion 1 (VuMATE1) under aluminum (Al(3+) ) stress. However, the underlying mechanisms regulating VuMATE1 expression remain unknown. We isolated and characterized a gene encoding Sensitive to Proton Rhizotoxicity1 (STOP1)-like protein, VuSTOP1, from rice bean. The role of VuSTOP1 in regulating VuMATE1 expression was investigated using the yeast one-hybrid assay. We characterized the function of VuSTOP1 in Al(3)  (+)  - and H(+) -tolerance using in planta complementation assays. We demonstrated that VuSTOP1 has transactivation potential. We found that VuSTOP1 expression is inducible by Al(3+) and H(+) stress. However, although VuSTOP1 binds to the promoter of VuMATE1, the inconsistent tissue localization patterns of VuSTOP1 and VuMATE1 preclude VuSTOP1 as the major factor regulating VuMATE1 expression. In addition, when a protein translation inhibitor increased expression of VuSTOP1, VuMATE1 expression was inhibited. In planta complementation assay demonstrated that VuSTOP1 could fully restore expression of genes involved in H(+) tolerance, but could only partially restore expression of AtMATE. We conclude that VuSTOP1 plays a major role in H(+) tolerance, but only a minor role in Al(3+) tolerance. The differential transcriptional regulation of VuSTOP1 and VuMATE1 reveals a complex regulatory system controlling VuMATE1 expression.

Proteomics of aluminum tolerance in plants.

Aluminum (Al) toxicity is a major constraint for plant root development and growth as well as crop yield in acidic soils, which constitute approximately 40% of the potentially arable lands worldwide. The mechanisms of Al tolerance in plants are not well understood. As a whole systems approach, proteomic techniques have proven to be crucial as a complementary strategy to explore the mechanism in Al toxicity. Review here focuses on the potential of proteomics to unravel the common and plant species-specific changes at proteome level under Al stress, via comparative analysis of the Al-responsive proteins uncovered by recent proteomic studies using 2DE. Understanding the mechanisms of Al tolerance in plants is critical to generate Al resistance crops for developing sustainable agriculture practices, thereby contributing to food security worldwide.