Targeting aquaporins to alleviate hazardous metal(loid)s imposed stress in plants
Graphical Abstract
Introduction
Stress imposed in plants by hazardous heavy metals and metalloids (metal(loid)s), their toxicity, and the resulting adverse effects on the food chain and the surrounding environment are still topical. Heavy metals have relatively high density, atomic number, atomic weight, and a specific gravity greater than 5.0. Naturally, heavy metals are mostly found in soil and aquatic ecosystems. Some of the heavy metals like iron (Fe), zinc (Zn), and copper (Cu) are considered essential for plants and animals since they play a significant role in physiological and biochemical functions (Wintz et al., 2002). However, metal(loid)s like lead (Pb), arsenic (As), mercury (Hg), cadmium (Cd), barium (Ba), chromium (Cr), selenium (Se), nickel (Ni), cobalt (Co), and silver (Ag) are considered toxic or poisonous even at low levels and are significant environmental pollutants. Some of these elements like As and Se have properties in between metals and non-metals and categorized as metalloids, but commonly considered as a member of heavy metals. Heavy metal (considered both metal and metalloids) stress has a negative impact on the normal functioning of plants and the environmental health of soil organisms (Bhat et al., 2019, Carrier et al., 2003, DalCorso et al., 2010, Sharma and Dubey, 2007). Crop plants growing in heavy metal polluted areas show a drastic reduction in growth and yield (Shivaraj et al., 2019, Wang et al., 2016). Anthropogenic activities such as mining, energy production, smelting operations, and agricultural activities increase heavy metal pollution. As a consequence, plants take up these element at such elevated levels where even essential elements can cause deleterious effects. The heavy metal polluted areas are increasing exponentially worldwide which is causing extensive losses in agricultural produce as well as imposing a great risk to domestic animals and human health (Ratcliffe et al., 2017, Shivaraj et al., 2020). Widespread areas in countries such as Albania and North Greece have been polluted with heavy metals like Pb, Cu, and Cd (Shallari et al., 1998, Zantopoulos et al., 1999) and Cd, Cu, and Zn in China, Japan and Indonesia (Herawati et al., 2000). Moreover, approximately 720 sites on the National Priority List (NPL) of the United States are contaminated with heavy metals (Mulligan et al., 2001). Heavy metal pollution and the accumulation of metals in soil impose many challenges for agriculture. It can adversely affect crop growth, crop productivity, food safety, and marketability. Further, accumulation of heavy metals also causes necrosis, chlorosis in younger leaves, turgor loss, crippled photosynthetic apparatus, reduction in seed germination, and reduction in growth (Carrier et al., 2003, DalCorso et al., 2010, Sharma and Dubey, 2007). Thus, contamination of agricultural soil has become a serious issue globally, and the need for understanding the mechanisms involved in heavy metal stress tolerance is therefore a subject of highest priority.
More extensive efforts using versatile approaches and tools are needed to develop novel crop varieties with better tolerance against heavy metals. Recent advances in genomics, transcriptomics, metabolomics, and proteomics have aided the identification and characterization of genes regulating heavy metal uptake, accumulation, and different molecular mechanisms providing tolerance. Such genes can be exploited for the development of heavy metal tolerant crop varieties (Singh et al., 2016).
Aquaporins (AQPs) are one of the prime candidates thought to play a critical role in heavy metal stress tolerance (Przedpelska-Wasowicz and Wierzbicka, 2011, Shivaraj et al., 2019). The prime discovery of AQPs by Peter Agre and his colleagues leads a path to study the role of AQPs in physiological processes such as biotic and abiotic stress including heavy metal stress in plants (Johansson et al., 2000, Preston and Agre, 1991, Preston et al., 1992, Tyerman et al., 1999). Aquaporins are channel forming transmembrane proteins that allow the passage of water molecules and other small solutes across the bio-membranes. Aquaporins are mostly homo-tetramers of four identical subunits, with each subunit having a typical six membrane-spanning helices (H1 - H6) intertwined with five loops (A - E). Solute transport through the AQPs is tightly regulated and has a great level of solute specificity. The selective permeability of AQPs is regulated by two constrictions which include, conserved NPA (asparagine-proline-alanine) motifs present at loop B and loop E and aromatic arginine selectivity filter (ar/R) comprises of four amino acids residues on H2, H5, LE1, and LE2. Based on the sequence similarity and the subcellular localization, the AQP family in higher plants have been further classified into five subfamilies namely, plasma membrane intrinsic proteins (PIPs), the tonoplast intrinsic proteins (TIPs), the nodulin26-like intrinsic proteins (NIPs), the small basic intrinsic proteins (SIPs) and the uncategorized intrinsic proteins (XIPs) (Chaumont et al., 2001, Johanson et al., 2001, Kaldenhoff and Fischer, 2006, Quigley et al., 2001).
In the present article, we have discussed the uptake and transport of water and other solutes by AQPs under heavy metal stress. Emphasis is given on studies suggesting a role of AQPs in improving plant resilience under stress. Defining the solute specificity, gating mechanism, transcriptional, and post-translational regulation of AQPs will provide an opportunity to make desired genetic manipulations enhancing stress tolerance. A better understanding of the AQP transport system will help to accelerate translational research required to engineer stress-tolerant crop varieties. In this regard, recent technological advancements for studying AQPs have been described in detail. In addition, efficient exploration of approaches like transgenic development and genome editing to achieve desired manipulations are discussed. The review addresses the present understanding of AQPs, knowledge gaps, and opportunities for translational research. Providing a whole picture of the different aspects of AQPs that can be utilized for the production of superior designer crops is the major objective of this review.
Section snippets
Effect of heavy metal on water uptake at root level and transport to different aerial tissues
Roots, playing major functions of the absorption of water and nutrients uptake, anchoring the plant body, are also the first site of contact for heavy metals (Barcelo et al., 1988, Becerril et al., 1989, Burkhead et al., 2009, Feleafel and Mirdad, 2013). Generally, a very minor portion of the heavy metals present in the soil is translocated to the above ground parts, even though it cause numerous phytotoxic effects in plants. Phytotoxic effects due to heavy metals on plant majorly include
Role of aquaporin under heavy metal stress
Aquaporins, a class of water channel proteins permeate major transmembrane water flow in most of the organisms including plants. Aquaporins function both by alterations in the conductivity as well as expression patterns. The conductivity of AQPs is altered in response to heavy metal stress leading to a decrease in membrane water permeability as reported in epidermal cells of Alium cepa in response to Cd, Hg, Pb, and Zn (Przedpelska-Wasowicz and Wierzbicka, 2011). The gating of AQPs starting
Advanced tools and techniques for aquaporin studies
The advancement in the computational tools and the availability of omics scale data like genomic, transcriptomic, and proteomic data enables the detailed study of AQPs in plants. Numerous computational tools and analytical pipelines are available to predict the 3D structure, conserved motifs and domains, pore structure, pore size, cavities, sub-cellular localization, phosphorylation sites, heterodimerization, expression profile, and co-expression network of AQPs (Deshmukh et al., 2016). In
Differential expression of aquaporins under heavy metal(loid) stress in plants
Numerous comparative transcriptomic studies have elaborated differential responses of AQPs under various abiotic stresses, including heavy metal stresses (Table 1). For instance, PIPs are a major class of AQPs found to be down-regulated in B. juncea plants exposed to As(III) which led to decreased water content and inhibited seedling growth (Srivastava et al., 2013). Till now very less is known about the transcriptional regulation of AQPs under Cd stress, but one report from barley roots
Metal and non-metal inhibitors of aquaporins
Various metal and non-metal ions act as inhibitors of plant AQPs and provide both detrimental as well as beneficial effects on plant growth (Table 2). Particularly mercuric chloride (HgCl2), a major inhibitor of AQPs, has been regularly used to test AQP activity in both plants and animals (Maggio and Joly, 1995). Mercuric chloride mediated inhibition of AQUA1 has been reported in poplar (Ariani et al., 2019). Many previous studies suggest that sub-millimolar concentrations of Hg or mercurial
Regulation of aquaporins gating mechanism by heavy metals
The AQP gating mechanism (opening and closing of water channels) plays a vital role in the regulation of water passage across the biomembrane. One of the pioneer studies (Törnroth-Horsefield et al., 2006) put forth comprehensive efforts to describe the high-resolution structure of plant AQP which shed light to understand the molecular gating mechanism of AQP. They disclose the X-ray structure of Spinach oleracea plasma membrane AQP (SoPIP2;1) in its open and closed conformations with a
Mechanisms involved in AQP-mediated regulation of heavy metal(loid) stresses
Efflux is one of the predominant mechanisms utilized by plants for resisting the stress imposed by hazardous metal(loid)s. Multiple reports suggest the impending importance of efflux transporters in detoxification by excreting hazardous metal(loid)s out of the cell (Singh et al., 2015, Singh et al., 2016). Many AQPs have such efflux transporter activity. The AQP involved in As(III) uptake in rice, Lsi1 (Oryza sativa NIP2:1), is also engaged in As(III) efflux (Zhao et al., 2010). In addition to
Heterologous expression of plant aquaporin showing enhanced heavy-metal resistance
Multiple instances of heterologous expression of AQPs, have been performed for functional annotations, to increase heavy metal tolerance in crops, or for phytoremediation purposes (Table 3). For functional annotations, heterologous expression in Xenopus oocytes and Saccharomyces cerevisiae are mostly preferred approaches. Heterologous expression of AtNIP1;7 in yeast acr3Δ genotype showed the increased uptake of As(III) (Isayenkov and Maathuis, 2008) confirming its role in As(III) uptake in
Identification of desired AQP alleles (allele mining) and marker-assisted breeding
Sequencing of diverse crop plants has led to the aggregation of a vast amount of information in the public domain that can be used to isolate superior alleles of genes associated with agronomically important traits. For the dissection of natural variation occurring in candidate genes, allele mining is a promising approach that can be exploited for the identification of novel haplotypes, and also in the understanding of gene evolution. Identification of novel alleles helps in the development of
Summary and future perspectives
Numerous physiological fluctuations have been reported in the plants as a consequence of heavy metal stress as discussed in the present article. Alteration in water status is one of the earliest responses in plants when subjected to heavy metal stresses. Heavy metals reduce water uptake by roots as well as affect short distance transport of water across different tissues. The heavy metals induced alterations are attributed largely to differential expression of AQPs involved in water homeostasis
CRediT authorship contribution statement
Sanskriti Vats, Sreeja Sudhakarn, Anupriya Bhardwaj: Wrote the original draft. Sanskriti Vats, Yogesh Sharma, Sreeja Sudhakarn: Contributed in Visualization. Sudhir Kumar, Humira Sonah, Tilak Raj Sharma, Rupesh Deshmukh: Conceptualized, Writing - review & editing. Rupesh Deshmukh: Supervised. All the authors read and approved the final draft.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are thankful to the Department of Biotechnology, Government of India for the Ramalingaswami Fellowship Award to Humira Sonah and Rupesh Deshmukh; Department of Science and Technology, India for JC Bose Fellowship to Tilakraj Sharma and funding support (CRG/2019/006599) to Rupesh Deshmukh; Council of Scientific & Industrial Research (CSIR), India for granting Shyama Prasad Mukherjee Fellowship (SPMF) to Sanskriti Vats, and Junior Research Fellowship to Sreeja Sudhakarn and Yogesh
References (174)
- et al.
The aquaporins, blueprints for cellular plumbing systems
J. Biol. Chem.
(1998) - et al.
Ser123 is essential for the water channel activity of McPIP2; 1 from Mesembryanthemum crystallinum
J. Biol. Chem.
(2010) - et al.
AQUA1 is a mercury sensitive poplar aquaporin regulated at transcriptional and post-translational levels by Zn stress
Plant Physiol. Biochem.
(2019) - et al.
Identification and characterization of two plasma membrane aquaporins in durum wheat (Triticum turgidum L. subsp. durum) and their role in abiotic stress tolerance
Plant Physiol. Biochem.
(2011) - et al.
Cadmium-induced decrease of water stress resistance in bush bean plants (Phaseolus vulgaris L. cv. Contender) I. Effects of Cd on water potential, relative water content, and cell wall elasticity
J. Plant Physiol.
(1986) - et al.
Mercury-induced conformational changes and identification of conserved surface loops in plasma membrane aquaporins from higher plants TOPOLOGY OF PMIP31 FROM Beta vulgaris L
J. Biol. Chem.
(1997) - et al.
Root based responses account for Psidium guajava survival at high nickel concentration
J. Plant Physiol.
(2015) Inhibitors of the proton-sucrose symport
Arch. Biochem. Biophys.
(1993)- et al.
Transpiration response of de-rooted peanut plants to aquaporin inhibitors
Environ. Exp. Bot.
(2012) - et al.
Silver and zinc inhibitors influence transpiration rate and aquaporin transcript abundance in intact soybean plants
Environ. Exp. Bot.
(2016)
Biotechnological approaches for phytoremediation
Engineering introns to express RNA guides for Cas9-and Cpf1-mediated multiplex genome editing
Mol. Plant.
Copper-induced alterations in structure and proliferation of maize root meristem cells
J. Plant Physiol.
Unravelling cadmium toxicity and tolerance in plants: insight into regulatory mechanisms
Environ. Exp. Bot.
Cloning and characterization of ZmPIP1-5b, an aquaporin transporting water and urea
Plant Sci.
The Arabidopsis thaliana aquaglyceroporin AtNIP7; 1 is a pathway for arsenite uptake
FEBS Lett.
Aquaporin homologues in plants and mammals transport ammonia
FEBS Lett.
The Camelina aquaporin CsPIP2; 1 is regulated by phosphorylation at Ser273, but not at Ser277, of the C-terminus and is involved in salt-and drought-stress responses
J. Plant Physiol.
The role of aquaporins in cellular and whole plant water balance
Biochim. Biophys. Acta Biomembr.
Functional aquaporin diversity in plants
Biochim. Biophys. Acta Biomembr.
NIP1; 1, an aquaporin homolog, determines the arsenite sensitivity of Arabidopsis thaliana
J. Biol. Chem.
A defect in the yeast plasma membrane urea transporter Dur3p is complemented by CpNIP1, a Nod26–like protein from zucchini (Cucurbita pepo L.), and by Arabidopsis thaliana δ‐TIP or γ‐TIP
FEBS Lett.
Association study reveals genetic loci responsible for arsenic, Cadmium and Lead Accumulation in Rice Grain in Contaminated Farmlands
Front. Plant Sci.
Plant aquaporins: roles in plant physiology
Biochim. Biophys. Acta Gen. Subj.
Prime editing: a new way for genome editing
Trends Cell Biol.
Overview of free software developed for designing drugs based on protein-small molecules interaction
Curr. Top. Med. Chem.
Overexpression of a plasma membrane aquaporin in transgenic tobacco improves plant vigor under favorable growth conditions but not under drought or salt stress
Plant Cell
Silicon induced antioxidative responses and expression of BOR2 and two PIP family aquaporin genes in barley grown under boron toxicity
Plant Mol. Biol. Rep.
Heterologous expression of the yeast arsenite efflux system ACR3 improves Arabidopsis thaliana tolerance to arsenic stress
New Phytol.
Silver nanoparticles in soil–plant systems
J. Nanopart. Res.
Search-and-replace genome editing without double-strand breaks or donor DNA
Nature
Over-expression of AQUA1 in Populus alba Villafranca clone increases relative growth rate and water use efficiency, under Zn excess condition
Plant Cell Rep.
Genome-wide identification and characterization of aquaporin gene family in common bean (Phaseolus vulgaris L.)
Mol. Genet. Genom.
Transcriptome analyses of Populus× euramericana clone I-214 leaves exposed to excess zinc
Tree Physiol.
Genome-wide analysis of major intrinsic proteins in the tree plant Populus trichocarpa: characterization of XIP subfamily of aquaporins from evolutionary perspective
BMC Plant Biol.
Plant water relations as affected by heavy metal stress: a review
J. Plant Nutr.
Structural and ultrastructural disorders in cadmium‐treated bush bean plants (Phaseolus vulgaris L.)
New Phytol.
New insights into the regulation of aquaporins by the arbuscular mycorrhizal symbiosis in maize plants under drought stress and possible implications for plant performance
Mol. Plant Microbe Inter.
Changes induced by cadmium and lead in gas exchange and water relations
Plant Physiol. Biochem.
Selective regulation of maize plasma membrane aquaporin trafficking and activity by the SNARE SYP121
Plant Cell
Role of silicon in mitigation of heavy metal stresses in crop plants
Plants
Enhancing gene targeting with designed zinc finger nucleases
Science
The Nicotiana tabacum plasma membrane aquaporin NtAQP1 is mercury‐insensitive and permeable for glycerol
Plant J.
A subgroup of plant aquaporins facilitate the bi-directional diffusion of As (OH) 3 and Sb (OH) 3 across membranes
BMC Biol.
Copper homeostasis
New Phytol.
Multiplexed genome engineering by Cas12a and CRISPR arrays encoded on single transcripts
Nat. Methods
Cadmium distribution and microlocalization in oilseed rape (Brassica napus) after long-term growth on cadmium-contaminated soil
Planta
Responses of wheat plants to nutrient deprivation may involve the regulation of water-channel function
Planta
Aquaporins constitute a large and highly divergent protein family in maize
Plant Physiol.
Multiplexed activation of endogenous genes by CRISPR-on, an RNA-guided transcriptional activator system
Cell Res.
Cited by (24)
Structural assessment of OsNIP2;1 highlighted critical residues defining solute specificity and functionality of NIP class aquaporins
2024, Journal of Advanced ResearchAnalysis of multiple biomarkers revealed the size matters of Cu particles for barley response under foliar exposure
2024, Science of the Total EnvironmentDifferences in mineral and osmotic balances enhance zinc translocation in an aquaporin overexpressing poplar
2024, Plant Physiology and BiochemistryDurability of antimicrobial agent on nanofiber: A collective review from 2018 to 2022
2024, Journal of Industrial and Engineering ChemistryInteraction between selenium and essential micronutrient elements in plants: A systematic review
2022, Science of the Total EnvironmentCitation Excerpt :These results strongly support that Se has beneficial effects on Na+ compartmentalization in root vacuoles under saline stress. Aquaporins function widely in ion and water uptake and are involved in heavy metal tolerance in plants (Vats et al., 2021). The transcript level of aquaporins was enhanced in M. hupehensis roots under high-salinity conditions.