Aquaporins as potential drought tolerance inducing proteins: Towards instigating stress tolerance

Insights into the effects of saline forage on the meat quality of Tibetan sheep by metabolome and multivariate analysis

This work aimed to investigate how two different types of forage (saline and alkaline) impact the meat quality and muscle metabolism of Tibetan sheep. An integrative multi-omics analysis of meat quality and different metabolites was performed using untargeted and targeted metabolomics approaches. The research results indicated that GG grass (saline and alkaline forage) possessed superior characteristics in terms of apparent quality and secondary metabolite content compared with HG grass (Non saline alkali forage), regardless of the targeted metabolites or non-targeted ones. Simultaneously, under stress conditions, the carbohydrates-rich salt-alkali grass play a significant role in slowing down the decline in pH, increasing the unsaturated fatty acid content and reducing the thawing loss in Tibetan sheep. This study provides an understanding of the impact of different salt-alkali grass on the quality of Tibetan sheep meat, while providing a scientific basis for the future development of salt-alkali livestock industry.

Plant biomarkers as early detection tools in stress management in food crops: a review

MAIN CONCLUSION

Plant Biomarkers are objective indicators of a plant's cellular state in response to abiotic and biotic stress factors. They can be explored in crop breeding and engineering to produce stress-tolerant crop species. Global food production safely and sustainably remains a top priority to feed the ever-growing human population, expected to reach 10 billion by 2050. However, abiotic and biotic stress factors negatively impact food production systems, causing between 70 and 100% reduction in crop yield. Understanding the plant stress responses is critical for developing novel crops that can adapt better to various adverse environmental conditions. Using plant biomarkers as measurable indicators of a plant's cellular response to external stimuli could serve as early warning signals to detect stresses before severe damage occurs. Plant biomarkers have received considerable attention in the last decade as pre-stress indicators for various economically important food crops. This review discusses some biomarkers associated with abiotic and biotic stress conditions and highlights their importance in developing stress-resilient crops. In addition, we highlighted some factors influencing the expression of biomarkers in crop plants under stress. The information presented in this review would educate plant researchers, breeders, and agronomists on the significance of plant biomarkers in stress biology research, which is essential for improving plant growth and yield toward sustainable food production.

Regulation of drought tolerance in Arabidopsis involves the PLATZ4-mediated transcriptional repression of plasma membrane aquaporin PIP2;8

Plant A/T-rich protein and zinc-binding protein (PLATZ) transcription factors play important roles in plant growth, development and abiotic stress responses. However, how PLATZ influences plant drought tolerance remains poorly understood. The present study showed that PLATZ4 increased drought tolerance in Arabidopsis thaliana by causing stomatal closure. Transcriptional profiling analysis revealed that PLATZ4 affected the expression of a set of genes involved in water and ion transport, antioxidant metabolism, small peptides and abscisic acid (ABA) signaling. Among these genes, the direct binding of PLATZ4 to the A/T-rich sequences in the plasma membrane intrinsic protein 2;8 (PIP2;8) promoter was identified. PIP2;8 consistently reduced drought tolerance in Arabidopsis through inhibiting stomatal closure. PIP2;8 was localized in the plasma membrane, exhibited water channel activity in Xenopus laevis oocytes and acted epistatically to PLATZ4 in regulating the drought stress response in Arabidopsis. PLATZ4 increased ABA sensitivity through upregulating the expression of ABSCISIC ACID INSENSITIVE 3 (ABI3), ABI4 and ABI5. The transcripts of PLATZ4 were induced to high levels in vegetative seedlings under drought and ABA treatments within 6 and 3 h, respectively. Collectively, these findings reveal that PLATZ4 positively influences plant drought tolerance through regulating the expression of PIP2;8 and genes involved in ABA signaling.

Transcriptome Analysis Points to BES1 as a Transducer of Strigolactone Effects on Drought Memory in Arabidopsis thaliana

Strigolactones (SLs) are carotenoid-derived phytohormones governing a wide range of physiological processes, including drought-associated stomatal closure. We have previously shown in tomato that SLs regulate the so-called after-effect of drought, whereby stomatal conductance is not completely restored for some time during recovery after a drought spell, irrespective of the water potential. To ease the elucidation of its molecular underpinnings, we investigated whether this SL effect is conserved in Arabidopsis thaliana by contrasting the physiological performances of the wild-type with SL-depleted (more axillary growth 4, max4) and insensitive (dwarf 14, d14) mutants in a drought and recovery protocol. Physiological analyses showed that SLs are important to achieve a complete after-effect in A. thaliana, while transcriptome results suggested that the SL-dependent modulation of drought responses extends to a large subset (about 4/5) of genes displaying memory transcription patterns. Among these, we show that the activation of over 30 genes related to abscisic acid metabolism and signaling strongly depends on SL signaling. Furthermore, by using promoter-enrichment tools, we identified putative cis- and trans-acting factors that may be important in the SL-dependent and SL-independent regulation of genes during drought and recovery. Finally, in order to test the accuracy of our bioinformatic prediction, we confirmed one of the most promising transcription factor candidates mediating SL signaling effects on transcriptional drought memory-BRI-EMS SUPPRESSOR1 (BES1). Our findings reveal that SLs are master regulators of Arabidopsis transcriptional memory upon drought and that this role is partially mediated by the BES1 transcription factor.

Mechanism of [CO2] Enrichment Alleviated Drought Stress in the Roots of Cucumber Seedlings Revealed via Proteomic and Biochemical Analysis

Cucumber is one of the most widely cultivated greenhouse vegetables, and its quality and yield are threatened by drought stress. Studies have shown that carbon dioxide concentration ([CO₂]) enrichment can alleviate drought stress in cucumber seedlings; however the mechanism of this [CO₂] enrichment effect on root drought stress is not clear. In this study, the effects of different drought stresses (simulated with 0, 5% and 10% PEG 6000, i.e., no, moderate, and severe drought stress) and [CO₂] (400 μmol·mol^-1 and 800 ± 40 μmol·mol^-1) on the cucumber seedling root proteome were analyzed using the tandem mass tag (TMT) quantitative proteomics method. The results showed that after [CO₂] enrichment, 346 differentially accumulating proteins (DAPs) were found only under moderate drought stress, 27 DAPs only under severe drought stress, and 34 DAPs under both moderate and severe drought stress. [CO₂] enrichment promoted energy metabolism, amino acid metabolism, and secondary metabolism, induced the expression of proteins related to root cell wall and cytoskeleton metabolism, effectively maintained the balance of protein processing and degradation, and enhanced the cell wall regulation ability. However, the extent to which [CO₂] enrichment alleviated drought stress in cucumber seedling roots was limited under severe drought stress, which may be due to excessive damage to the seedlings.

Characterization, costs, cues and future perspectives of phenotypic plasticity

BACKGROUND

Plastic responses of plants to the environment are ubiquitous. Phenotypic plasticity occurs in many forms and at many biological scales, and its adaptive value depends on the specific environment and interactions with other plant traits and organisms. Even though plasticity is the norm rather than the exception, its complex nature has been a challenge in characterizing the expression of plasticity, its adaptive value for fitness and the environmental cues that regulate its expression.

SCOPE

This review discusses the characterization and costs of plasticity and approaches, considerations, and promising research directions in studying plasticity. Phenotypic plasticity is genetically controlled and heritable; however, little is known about how organisms perceive, interpret and respond to environmental cues, and the genes and pathways associated with plasticity. Not every genotype is plastic for every trait, and plasticity is not infinite, suggesting trade-offs, costs and limits to expression of plasticity. The timing, specificity and duration of plasticity are critical to their adaptive value for plant fitness.

CONCLUSIONS

There are many research opportunities to advance our understanding of plant phenotypic plasticity. New methodology and technological breakthroughs enable the study of phenotypic responses across biological scales and in multiple environments. Understanding the mechanisms of plasticity and how the expression of specific phenotypes influences fitness in many environmental ranges would benefit many areas of plant science ranging from basic research to applied breeding for crop improvement.

Ubiquitin ligase OsRINGzf1 regulates drought resistance by controlling the turnover of OsPIP2;1

Water is crucial for plant growth and survival. The transcellular water movement is facilitated by aquaporins (AQPs) that rapidly and reversibly modify water permeability. The abundance of AQPs is regulated by its synthesis, redistribution and degradation. However, the molecular mechanism of proteasomal degradation of AQPs remains unclear. Here, we demonstrate that a novel E3 ligase, OsRINGzf1, mediated the degradation of AQPs in rice. OsRINGzf1 is the candidate gene from a drought-related quantitative trait locus (QTL) on the long arm of chromosome 4 in rice (Oryza sativa) and encodes a Really Interesting New Gene (RING) zinc finger protein 1. OsRINGzf1 possesses the E3 ligase activity, ubiquitinates and mediates OsPIP2;1 degradation, thus reducing its protein abundance. The content of OsPIP2;1 protein was decreased in OsRINGzf1 overexpression (OE) plants. The degradation of OsPIP2;1 was inhibited by MG132. The OsRINGzf1 OE plants, with higher leaf-related water content (LRWC) and lower leaf water loss rate (LWLR), exhibited enhanced drought resistance, whereas the RNAi and knockout plants of OsRINGzf1 were more sensitive to drought. Together, our data demonstrate that OsRINGzf1 positively regulates drought resistance through promoting the degradation of OsPIP2;1 to enhance water retention capacity in rice.

The Hidden Intricacies of Aquaporins: Remarkable Details in a Common Structural Scaffold

Evolution turned aquaporins (AQPs) into the most efficient facilitators of passive water flow through cell membranes at no expense of solute discrimination. In spite of a plethora of solved AQP structures, many structural details remain hidden. Here, by combining extensive sequence- and structural-based analysis of a unique set of 20 non-redundant high-resolution structures and molecular dynamics simulations of four representatives, key aspects of AQP stability, gating, selectivity, pore geometry, and oligomerization, with a potential impact on channel functionality, are identified. The general view of AQPs possessing a continuous open water pore is challenged and it is depicted that AQPs' selectivity is not exclusively shaped by pore-lining residues but also by the relative arrangement of transmembrane helices. Moreover, this analysis reveals that hydrophobic interactions constitute the main determinant of protein thermal stability. Finally, a numbering scheme of the conserved AQP scaffold is established, facilitating direct comparison of, for example, disease-causing mutations and prediction of potential structural consequences. Additionally, the results pave the way for the design of optimized AQP water channels to be utilized in biotechnological applications.

Genome-Wide Characterization of the Aquaporin Gene Family in Radish and Functional Analysis of RsPIP2-6 Involved in Salt Stress

Aquaporins (AQPs) constitute a highly diverse family of channel proteins that transport water and neutral solutes. AQPs play crucial roles in plant development and stress responses. However, the characterization and biological functions of RsAQPs in radish (Raphanus sativus L.) remain elusive. In this study, 61 non-redundant members of AQP-encoding genes were identified from the radish genome database and located on nine chromosomes. Radish AQPs (RsAQPs) were divided into four subfamilies, including 21 plasma membrane intrinsic proteins (PIPs), 19 tonoplast intrinsic proteins (TIPs), 16 NOD-like intrinsic proteins (NIPs), and 5 small basic intrinsic proteins (SIPs), through phylogenetic analysis. All RsAQPs contained highly conserved motifs (motifs 1 and 4) and transmembrane regions, indicating the potential transmembrane transport function of RsAQPs. Tissue- and stage-specific expression patterns of AQP gene analysis based on RNA-seq data revealed that the expression levels of PIPs were generally higher than TIPs, NIPs, and SIPs in radish. In addition, quantitative real-time polymerase chain reaction (qRT-PCR) revealed that seven selected RsPIPs, according to our previous transcriptome data (e.g., RsPIP1-3, 1-6, 2-1, 2-6, 2-10, 2-13, and 2-14), exhibited significant upregulation in roots of salt-tolerant radish genotype. In particular, the transcriptional levels of RsPIP2-6 dramatically increased after 6 h of 150 mM NaCl treatment during the taproot thickening stage. Additionally, overexpression of RsPIP2-6 could enhance salt tolerance by Agrobacterium rhizogenes-mediated transgenic radish hairy roots, which exhibited the mitigatory effects of plant growth reduction, leaf relative water content (RWC) reduction and alleviation of O2- in cells, as shown by nitro blue tetrazolium (NBT) staining, under salt stress. These findings are helpful for deeply dissecting the biological function of RsAQPs on the salt stress response, facilitating practical application and genetic improvement of abiotic stress resistance in radish.

Pearl Millet Aquaporin Gene PgPIP2;6 Improves Abiotic Stress Tolerance in Transgenic Tobacco

Pearl millet [Pennisetum glaucum (L) R. Br.] is an important cereal crop of the semiarid tropics, which can withstand prolonged drought and heat stress. Considering an active involvement of the aquaporin (AQP) genes in water transport and desiccation tolerance besides several basic functions, their potential role in abiotic stress tolerance was systematically characterized and functionally validated. A total of 34 AQP genes from P. glaucum were identified and categorized into four subfamilies, viz., plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), nodulin-26-like intrinsic proteins (NIPs), and small basic intrinsic proteins (SIPs). Sequence analysis revealed that PgAQPs have conserved characters of AQP genes with a closer relationship to sorghum. The PgAQPs were expressed differentially under high vapor pressure deficit (VPD) and progressive drought stresses where the PgPIP2;6 gene showed significant expression under high VPD and drought stress. Transgenic tobacco plants were developed by heterologous expression of the PgPIP2;6 gene and functionally characterized under different abiotic stresses to further unravel their role. Transgenic tobacco plants in the T2 generations displayed restricted transpiration and low root exudation rates in low- and high-VPD conditions. Under progressive drought stress, wild-type (WT) plants showed a quick or faster decline of soil moisture than transgenics. While under heat stress, PgPIP2;6 transgenics showed better adaptation to heat (40°C) with high canopy temperature depression (CTD) and low transpiration; under low-temperature stress, they displayed lower transpiration than their non-transgenic counterparts. Cumulatively, lower transpiration rate (Tr), low root exudation rate, declined transpiration, elevated CTD, and lower transpiration indicate that PgPIP2;6 plays a role under abiotic stress tolerance. Since the PgPIP2;6 transgenic plants exhibited better adaptation against major abiotic stresses such as drought, high VPD, heat, and cold stresses by virtue of enhanced transpiration efficiency, it has the potential to engineer abiotic stress tolerance for sustained growth and productivity of crops.

Understanding aquaporin regulation defining silicon uptake and role in arsenic, antimony and germanium stress in pigeonpea (Cajanus cajan)

Understanding of aquaporins (AQPs) facilitating the transport of water and many other small solutes including metalloids like silicon (Si) and arsenic (As) is important to develop stress tolerant cultivars. In the present study, 40 AQPs were identified in the genome of pigeonpea (Cajanus cajan), a pulse crop widely grown in semi-arid region and areas known to affected with heavy metals like As. Conserved domains, variation at NPA motifs, aromatic/arginine (ar/R) selectivity filters, and pore morphology defined here will be crucial in predicting solute specificity of pigeonpea AQPs. The study identified CcNIP2-1 as an AQP predicted to transporter Si (beneficial element) as well as As (hazardous element). Further Si quantification in different tissues showed about 1.66% Si in leaves which confirmed the predictions. Furthermore, scanning electron microscopy showed a higher level of Si accumulation in trichomes on the leaf surface. A significant alleviation in level of As, Sb and Ge stress was also observed when these heavy metals were supplemented with Si. Estimation of relative water content, H₂O₂, lipid peroxidation, proline, total chlorophyll content and other physiological parameters suggested Si derived stress tolerance. Extensive transcriptome profiling under different developmental stages from germination to senescence was performed to understand the tissue-specific regulation of different AQPs. For instance, high expression of TIP3s was observed only in reproductive tissues. Co-expression network developed using transcriptome data from 30 different conditions and tissues, showed interdependency of AQPs. Expression profiling of pigeonpea performed using real time PCR showed differential expression of AQPs after Si supplementation. The information generated about the phylogeny, distribution, molecular evolution, solute specificity, and gene expression dynamics in article will be helpful to better understand the AQP transport system in pigeonpea and other legumes.

Optimizing Crop Water Use for Drought and Climate Change Adaptation Requires a Multi-Scale Approach

Selection criteria that co-optimize water use efficiency and yield are needed to promote plant productivity in increasingly challenging and variable drought scenarios, particularly dryland cereals in the semi-arid tropics. Optimizing water use efficiency and yield fundamentally involves transpiration dynamics, where restriction of maximum transpiration rate helps to avoid early crop failure, while maximizing grain filling. Transpiration restriction can be regulated by multiple mechanisms and involves cross-organ coordination. This coordination involves complex feedbacks and feedforwards over time scales ranging from minutes to weeks, and from spatial scales ranging from cell membrane to crop canopy. Aquaporins have direct effect but various compensation and coordination pathways involve phenology, relative root and shoot growth, shoot architecture, root length distribution profile, as well as other architectural and anatomical aspects of plant form and function. We propose gravimetric phenotyping as an integrative, cross-scale solution to understand the dynamic, interwoven, and context-dependent coordination of transpiration regulation. The most fruitful breeding strategy is likely to be that which maintains focus on the phene of interest, namely, daily and season level transpiration dynamics. This direct selection approach is more precise than yield-based selection but sufficiently integrative to capture attenuating and complementary factors.

Increasing yield on dry fields: molecular pathways with growing potential

Drought stress constitutes one of the major constraints to agriculture all over the world, and its devastating effect is only expected to increase in the following years due to climate change. Concurrently, the increasing food demand in a steadily growing population requires a proportional increase in yield and crop production. In the past, research aimed to increase plant resilience to severe drought stress. However, this often resulted in stunted growth and reduced yield under favorable conditions or moderate drought. Nowadays, drought tolerance research aims to maintain plant growth and yield under drought conditions. Overall, recently deployed strategies to engineer drought tolerance in the lab can be classified into a 'growth-centered' strategy, which focuses on keeping growth unaffected by the drought stress, and a 'drought resilience without growth penalty' strategy, in which the main aim is still to boost drought resilience, while limiting the side effects on plant growth. In this review, we put the scope on these two strategies and some molecular players that were successfully engineered to generate drought-tolerant plants: abscisic acid, brassinosteroids, cytokinins, ethylene, ROS scavenging genes, strigolactones, and aquaporins. We discuss how these pathways participate in growth and stress response regulation under drought. Finally, we present an overview of the current insights and future perspectives in the development of new strategies to improve drought tolerance in the field.

Characterization of Differentially Expressed Genes under Salt Stress in Olive

Climate change, currently taking place worldwide and also in the Mediterranean area, is leading to a reduction in water availability and to groundwater salinization. Olive represents one of the most efficient tree crops to face these scenarios, thanks to its natural ability to tolerate moderate salinity and drought. In the present work, four olive cultivars (Koroneiki, Picual, Royal de Cazorla and Fadak86) were exposed to high salt stress conditions (200 mM of NaCl) in greenhouse, in order to evaluate their tolerance level and to identify key genes involved in salt stress response. Molecular and physiological parameters, as well as plant growth and leaves’ ions Na⁺ and K⁺ content were measured. Results of the physiological measurements showed Royal de Cazorla as the most tolerant cultivar, and Fadak86 and Picual as the most susceptible ones. Ten candidate genes were analyzed and their complete genomic, CDS and protein sequences were identified. The expression analysis of their transcripts through reverse transcriptase quantitative PCR (RT-qPCR) demonstrated that only OeNHX7, OeP5CS, OeRD19A and OePetD were upregulated in tolerant cultivars, thus suggesting their key role in the activation of a salt tolerance mechanism.

Scattering versus fluorescence self-quenching: more than a question of faith for the quantification of water flux in large unilamellar vesicles?

The endeavors to understand the determinants of water permeation through membrane channels, the effect of the lipid or polymer membrane on channel function, the development of specific water flow inhibitors, the design of artificial water channels and aquaporins for the use in industrial water filtration applications all rely on accurate ways to quantify water permeabilities (P f). A commonly used method is to reconstitute membrane channels into large unilamellar vesicles (LUVs) and to subject these vesicles to an osmotic gradient in a stopped-flow device. Fast recordings of either scattered light intensity or fluorescence self-quenching signals are taken as a readout for vesicle volume change, which in turn can be recalculated to accurate P f values. By means of computational and experimental data, we discuss the pros and cons of using scattering versus self-quenching experiments or subjecting vesicles to hypo- or hyperosmotic conditions. In addition, we explicate for the first time the influence of the LUVs size distribution, channel distribution between vesicles and remaining detergent after protein reconstitution on P f values. We point out that results such as the single channel water permeability (p f) depend on the membrane matrix or on the direction of the applied osmotic gradient may be direct results of the measurement and analysis procedure.

A draft genome provides hypotheses on drought tolerance in a keystone plant species in Western North America threatened by climate change

Climate change presents distinct ecological and physiological challenges to plants as extreme climate events become more common. Understanding how species have adapted to drought, especially ecologically important nonmodel organisms, will be crucial to elucidate potential biological pathways for drought adaptation and inform conservation strategies. To aid in genome-to-phenome research, a draft genome was assembled for a diploid individual of Artemisia tridentata subsp. tridentata, a threatened keystone shrub in western North America. While this taxon has few genetic resources available and genetic/genomics work has proven difficult due to genetic heterozygosity in the past, a draft genome was successfully assembled. Aquaporin (AQP) genes and their promoter sequences were mined from the draft genome to predict mechanisms regulating gene expression and generate hypotheses on key genes underpinning drought response. Fifty-one AQP genes were fully assembled within the draft genome. Promoter and phylogenetic analyses revealed putative duplicates of A. tridentata subsp. tridentata AQPs which have experienced differentiation in promoter elements, potentially supporting novel biological pathways. Comparison with nondrought-tolerant congener supports enrichments of AQP genes in this taxon during adaptation to drought stress. Differentiation of promoter elements revealed that paralogues of some genes have evolved to function in different pathways, highlighting these genes as potential candidates for future research and providing critical hypotheses for future genome-to-phenome work.

The Role of Plant-Associated Bacteria, Fungi, and Viruses in Drought Stress Mitigation

Drought stress is an alarming constraint to plant growth, development, and productivity worldwide. However, plant-associated bacteria, fungi, and viruses can enhance stress resistance and cope with the negative impacts of drought through the induction of various mechanisms, which involve plant biochemical and physiological changes. These mechanisms include osmotic adjustment, antioxidant enzyme enhancement, modification in phytohormonal levels, biofilm production, increased water and nutrient uptake as well as increased gas exchange and water use efficiency. Production of microbial volatile organic compounds (mVOCs) and induction of stress-responsive genes by microbes also play a crucial role in the acquisition of drought tolerance. This review offers a unique exploration of the role of plant-associated microorganisms-plant growth promoting rhizobacteria and mycorrhizae, viruses, and their interactions-in the plant microbiome (or phytobiome) as a whole and their modes of action that mitigate plant drought stress.

Comprehensive RNA-seq analysis revealed molecular pathways and genes associated with drought tolerance in wild soybean (Glycine soja Sieb. and Zucc.)

Drought stress at the germination stage is an important environmental stress limiting crop yield. Hence, our study investigated comparative root transcriptome profiles of four contrasting soybean genotypes viz., drought-tolerant (PI342618B/DTP and A214/DTL) and drought-sensitive (NN86-4/DSP and A195/DSL) under drought stress using RNA-Seq approach. A total of 4850 and 6272 differentially expressed genes (DEGs) were identified in tolerant (DTP and DTL) and sensitive (DSP and DSL) genotypes, respectively. Principle component analysis (PCA) and correlation analysis revealed higher correlation between DTP and DTL. Both gene ontology (GO) and MapMan analyses showed that the drought response was enriched in DEGs associated with water and auxin transport, cell wall/membrane, antioxidant activity, catalytic activity, secondary metabolism, signaling and transcription factor (TF) activities. Out of 981 DEGs screened from above terms, only 547 showed consistent opposite expression between contrasting genotypes. Twenty-eight DEGs of 547 were located on Chr.08 rich in QTLs and "Hotspot regions" associated with drought stress, and eight of them showed non-synonymous single nucleotide polymorphism. Hence, 10 genes (including above eight genes plus two hub genes) were predicated as possible candidates regulating drought tolerance, which needs further functional validation. Overall, the transcriptome profiling provided in-depth understanding about the genetic mechanism and candidate genes underlying drought tolerance in soybean.

Plant aquaporins alleviate drought tolerance in plants by modulating cellular biochemistry, root-architecture, and photosynthesis

Water is a vital resource for plants to grow, thrive, and complete their life cycle. In recent years, drastic changes in the climate, especially drought frequency and severity, have increased, which reduces agricultural productivity worldwide. Aquaporins are membrane channels belonging to the major intrinsic protein superfamily, which play an essential role in cellular water and osmotic homeostasis of plants under both control and water deficit conditions. A genome-wide search reveals the vast availability of aquaporin isoforms, phylogenetic relationships, different families, conserved residues, chromosomal locations, and gene structure of aquaporins. Furthermore, aquaporins gating and subcellular trafficking are commonly controlled by phosphorylation, cytosolic pH, divalent cations, reactive oxygen species, and stoichiometry. Researchers have identified their involvement in regulating hydraulic conductance, root system architecture, modulation of abiotic stress-related genes, seed viability and germination, phloem loading, xylem water exit, photosynthetic parameters, and post-drought recovery. Remarkable effects following the change in aquaporin activity and/or gene expression have been observed on root water transport properties, nutrient acquisition, physiology, transpiration, stomatal aperture, gas exchange, and water use efficiency. The present review highlights the role of different aquaporin homologs under water-deficit stress condition in model and crop plants. Moreover, the opportunity and challenges encountered to explore aquaporins for engineering drought-tolerant crop plants are also discussed here.

Roles of Plant Glycine-Rich RNA-Binding Proteins in Development and Stress Responses

In recent years, much progress has been made in elucidating the functional roles of plant glycine-rich RNA-binding proteins (GR-RBPs) during development and stress responses. Canonical GR-RBPs contain an RNA recognition motif (RRM) or a cold-shock domain (CSD) at the N-terminus and a glycine-rich domain at the C-terminus, which have been associated with several different RNA processes, such as alternative splicing, mRNA export and RNA editing. However, many aspects of GR-RBP function, the targeting of their RNAs, interacting proteins and the consequences of the RNA target process are not well understood. Here, we discuss recent findings in the field, newly defined roles for GR-RBPs and the actions of GR-RBPs on target RNA metabolism.

Understanding aquaporin transport system, silicon and other metalloids uptake and deposition in bottle gourd (Lagenaria siceraria)

Aquaporins (AQPs) facilitates the transport of small solutes like water, urea, carbon dioxide, boron, and silicon (Si) and plays a critical role in important physiological processes. In this study, genome-wide characterization of AQPs was performed in bottle gourd. A total of 36 AQPs were identified in the bottle gourd, which were subsequently analyzed to understand the pore-morphology, exon-intron structure, subcellular-localization. In addition, available transcriptome data was used to study the tissue-specific expression. Several AQPs showed tissue-specific expression, more notably the LsiTIP3-1 having a high level of expression in flowers and fruits. Based on the in-silico prediction of solute specificity, LsiNIP2-1 was predicted to be a Si transporter. Silicon was quantified in different tissues, including root, young leaves, mature leaves, tendrils, and fruits of bottle gourd plants. More than 1.3% Si (d.w.) was observed in bottle gourd leaves, testified the in-silico predictions. Silicon deposition evaluated with an energy-dispersive X-ray coupled with a scanning electron microscope showed a high Si accumulation in the shaft of leaf trichomes. Similarly, co-localization of Si with arsenic and antimony was observed. Expression profiling performed with real-time quantitative PCR showed differential expression of AQPs in response to Si supplementation. The information provided in the present study will be helpful to better understand the AQP transport mechanism, particularly Si and other metalloids transport and localization in plants.

Targeting aquaporins to alleviate hazardous metal(loid)s imposed stress in plants

Uptake of hazardous metal(loid)s adversely affects plants and imposes a threat to the entire food chain. Here, the role of aquaporins (AQPs) providing tolerance against hazardous metal(loid)s in plants is discussed to provide a perspective on the present understanding, knowledge gaps, and opportunities. Plants adopt complex molecular and physiological mechanisms for better tolerance, adaptability, and survival under metal(loid)s stress. Water conservation in plants is one such primary strategies regulated by AQPs, a family of channel-forming proteins facilitating the transport of water and many other solutes. The strategy is more evident with reports suggesting differential expression of AQPs adopted by plants to cope with the heavy metal stress. In this regard, numerous studies showing enhanced tolerance against hazardous elements in plants due to AQPs activity are discussed. Consequently, present understanding of various aspects of AQPs, such as tertiary-structure, transport activity, solute-specificity, differential expression, gating mechanism, and subcellular localization, are reviewed. Similarly, various tools and techniques are discussed in detail aiming at efficient utilization of resources and knowledge to combat metal(loid)s stress. The scope of AQP transgenesis focusing on heavy metal stresses is also highlighted. The information provided here will be helpful to design efficient strategies for the development of metal(loid)s stress-tolerant crops.

Silicon in mitigation of abiotic stress-induced oxidative damage in plants

Accumulation of reactive oxygen species (ROS), and their destructive effects on cellular organelles are the hallmark features of plants exposed to abiotic stresses. Plants are well-equipped with defensive mechanisms like antioxidant systems to deal with ROS-induced oxidative stress. Silicon has been emerged as an important regulator of plant protective mechanisms under environmental stresses, which can be up-taken from soil through a system of various silicon-transporters. In plants, silicon is deposited underneath of cuticles and in the cell wall, and help plant cells reduce deleterious effects of stresses. Furthermore, silicon can provide resistance to ROS-toxicity, which often accounts for silicon-mediated improvement of plant tolerance to different abiotic constraints, including salinity, drought, and metal toxicity. Silicon enhances the ROS-detoxification ability of treated plants by modulating the antioxidant defense systems, and the expression of key genes associated with oxidative stress mitigation and hormone metabolism. Silicon also displays additive roles in ROS-elimination when supplied with other external stimuli. Here, we discuss recent findings on how silicon is able to modulate antioxidant defense of plants in response to oxidative stress triggered by different abiotic constraints. We also review interactions of silicon with other signaling molecules, including nitric oxide, ROS, polyamines, and phytohormones in the mediation of plant protection against abiotic stress-induced oxidative damage.

Fullerol C60(OH)24 Nanoparticles and Drought Impact on Wheat (Triticum aestivum L.) during Growth and Infection with Aspergillus flavus

Fullerol C₆₀(OH)₂₄ nanoparticles (FNP)-wheat-A. flavus interaction outcome is more complicated in the presence of drought. This study sheds light on how the presence of FNP affects food and feed safety from the perspective of mycotoxin contamination. The study aims to determine the influence of FNP at environmentally plausible concentrations on wheat growth under drought stress and on the aggressiveness of A. flavus during wheat germination, as well as the influence of FNP on the secondary metabolite profile during the inappropriate wheat storage. The co-occurrence of drought and FNP inhibited germination and shoot growth, while an application of FNP alone had no negative effect on plant growth. Wheat pre-treated with FNP showed a concentration dependent resistance pattern to A. flavus aggressiveness. Nevertheless, using a LC-MS/MS based multi-mycotoxin method, six secondary fungal metabolites: 3-nitropropionic acid (<LOD −775.7336 ± 10.7752 ng mL⁻¹), aflatoxin B1 (<LOD −6.78 ± 0.43 ng mL⁻¹) and B2 (<LOD −0.07 ± 0.00 ng mL⁻¹), aflatoxicol (<LOD −0.37 ± 0.16 ng mL⁻¹), kojic acid (<LOD −1337.87 ± 189.04 ng mL⁻¹), and O-methylsterigmatocystin (<LOD −0.17 ± 0.00 ng mL⁻¹), were detected. FNP affected secondary metabolism of A. flavus during inappropriate wheat storage and increased the concentration of secondary metabolites in a concentration-dependent pattern (3-nitropropionic acid and kojic acid). In addition, aflatoxicol production was provoked in FNP treated samples.

Zinc regulates the hydraulic response of maize root under water stress conditions

Zinc (Zn) is involved in plant growth and stress resistance and is known to increase crop yield. Here, we investigated the effect of Zn on water absorption in the roots of maize (Zea mays L.), a crop which is sensitive to Zn deficiency, during water stress conditions. Seedlings of the maize variety "Zhengdan 958" were cultivated with 0.1 or 6 μM ZnSO₄·7H₂O. To simulate drought stress, three-week-old seedlings were exposed to 15% polyethylene glycol (PEG). Root growth parameters, root antioxidant enzyme activity, root hydraulic conductivity, root aquaporin gene expression, root and leaf anatomy structure, leaf water potential, chlorophyll content, leaf area, and gas exchange parameters were measured. Under water stress, moderate Zn treatment promoted root growth; maintained root and leaf anatomy structural integrity. Moderate Zn significantly increased roots hydraulic conductivity (51%) and decreased roots antioxidant enzyme activity (POD: -11.1%, CAT: -35.1%, SOD: -3.1%) compared with low-level Zn under water stress. The expression of ZmPIP1;1, ZmPIP1;2, and ZmPIP2;2 was significantly higher with moderate Zn treatment than that of low-level Zn treatment. The leaf water potential, chlorophyll content, leaf area, and gas exchange parameters with moderate Zn treatment increased significantly under water stress compared with low-level Zn treatment. The moderate concentration of Zn improved root hydraulic conductivity in maize and increased resistance to simulated drought conditions by maintaining root structural integrity, decreasing antioxidant enzyme activity, and increasing aquaporin gene expression. Moderate Zn application increased root water absorption and leaf transpiration, thereby maintaining maize water balance under water stress conditions.

Molecular Characterization and Expression of Four Aquaporin Genes in Impatiens walleriana During Drought Stress and Recovery

Aquaporins comprise a large group of transmembrane proteins responsible for water transport, which is crucial for plant survival under stress conditions. Despite the vital role of aquaporins, nothing is known about this protein family in Impatiens walleriana, a commercially important horticultural plant, which is sensitive to drought stress. In the present study, attention is given to the molecular characterization of aquaporins in I. walleriana and their expression during drought stress and recovery. We identified four I. walleriana aquaporins: IwPIP1;4, IwPIP2;2, IwPIP2;7 and IwTIP4;1. All of them had conserved NPA motifs (Asparagine-Proline-Alanine), transmembrane helices (TMh), pore characteristics, stereochemical properties and tetrameric structure of holoprotein. Drought stress and recovery treatment affected the aquaporins expression in I. walleriana leaves, which was up- or downregulated depending on stress intensity. Expression of IwPIP2;7 was the most affected of all analyzed I. walleriana aquaporins. At 15% and 5% soil moisture and recovery from 15% and 5% soil moisture, IwPIP2;7 expression significantly decreased and increased, respectively. Aquaporins IwPIP1;4 and IwTIP4;1 had lower expression in comparison to IwPIP2;7, with moderate expression changes in response to drought and recovery, while IwPIP2;2 expression was of significance only in recovered plants. Insight into the molecular structure of I. walleriana aquaporins expanded knowledge about plant aquaporins, while its expression during drought and recovery contributed to I. walleriana drought tolerance mechanisms and re-acclimation.

Two Aquaporin Genes, GhPIP2;7 and GhTIP2;1, Positively Regulate the Tolerance of Upland Cotton to Salt and Osmotic Stresses

Aquaporins (AQPs) facilitate the transport of water and small molecules across intrinsic membranes and play a critical role in abiotic stresses. In this study, 111, 54, and 56 candidate AQP genes were identified in Gossypium hirsutum (AD₁), Gossypium arboreum (A₂), and Gossypium raimondii (D₅), respectively, and were further classified into five subfamilies, namely, plasma intrinsic protein (PIP), tonoplast intrinsic protein (TIP), nodulin 26-like intrinsic protein (NIP), small basic intrinsic protein (SIP), and uncategorized X intrinsic protein (XIP). Transcriptome analysis and quantitative real-time PCR (qRT-PCR) revealed some high-expression GhPIPs and GhTIPs (PIP and TIP genes in G. hirsutum, respectively) in drought and salt stresses. GhPIP2;7-silenced plants decreased in the chlorophyll content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity comparing the mock control (empty-vector) under 400 mM NaCl treatment, which indicated a positive regulatory role of GhPIP2;7 in salt tolerance of cotton. The GhTIP2;1-silenced cotton plants were more sensitive to osmotic stress. GhTIP2;1-overexpressed plants exhibited less accumulation of H₂O₂ and malondialdehyde but higher proline content under osmotic stress. In summary, our study elucidates the positive regulatory roles of two GhAQPs (GhPIP2;7 and GhTIP2;1) in salt and osmotic stress responses, respectively, and provides a new gene resource for future research.

Grapevine Responses to Heat Stress and Global Warming

The potential effects of the forthcoming climate change include the rising of the average annual temperature and the accumulation of extreme weather events, like frequent and severe heatwaves, a phenomenon known as global warming. Temperature is an important environmental factor affecting almost all aspects of growth and development in plants. The grapevine (Vitis spp.) is quite sensitive to extreme temperatures. Over the current century, temperatures are projected to continue rising with negative impacts on viticulture. These consequences range from short-term effects on wine quality to long-term issues such as the suitability of certain varieties and the sustainability of viticulture in traditional wine regions. Many viticultural zones, particularly in Mediterranean climate regions, may not be suitable for growing winegrapes in the near future unless we develop heat-stress-adapted genotypes or identify and exploit stress-tolerant germplasm. Grapevines, like other plants, have developed strategies to maintain homeostasis and cope with high-temperature stress. These mechanisms include physiological adaptations and activation of signaling pathways and gene regulatory networks governing heat stress response and acquisition of thermotolerance. Here, we review the major impacts of global warming on grape phenology and viticulture and focus on the physiological and molecular responses of the grapevine to heat stress.

Understanding aquaporin transport system in highly stress-tolerant and medicinal plant species Jujube (Ziziphus jujuba Mill.)

Jujube (Ziziphus jujubaMill.), a deciduous tree, is well known for its medicinal and nutritional values. Being an extremophile, it has an excellent capability to survive under arid conditions with limited water availability. In this regard, studying the role of water transport regulating proteins such as Aquaporins (AQPs) in jujube is of great importance. Aquaporins, channel-forming proteins are known to have a significant role in the transport of water and many other small solutes in plants. In the present study, computational approaches have identified 36 AQPs, which comprised of 12 NIPs (Nodulin 26-like intrinsic proteins), 10 PIPs (Plasma membrane intrinsic proteins), 10 TIPs (Tonoplast intrinsic proteins), 3 SIPs (Small intrinsic proteins), and 1 XIP (uncharacterized intrinsic protein). Conserved features of AQPs like asparagines-proline-alanine (NPA) amino acid motifs, aromatic/arginine (ar/R) selectivity filters, and Frogger's residues, having a significant role in solute specificity and transport, were also predicted. Homology-based tertiary (3D) structures of AQP_S were also resolved using various tools, and subsequently, pore-lining residues have been identified using the 3D structures. The information of pore morphology, along with the conserved features provided through this work, will be helpful to predict solute specificity of AQPs. Analysis of transcriptomic data revealed the tissue-specific or ubiquitous expression of several AQPs in different tissues of jujube. Interestingly, TIP3-1 was found to have fruit specific expression whereas most of the AQPs have a relatively low expression. Based on the present study and previous reports, TIP3s seems to have a significant role in seed desiccation processes. The findings presented here provide pivotal insights into the functions of extremophile specific AQPs, to better understand the role of AQPs and, subsequently, the stress tolerance mechanism in jujube.

Membrane-associated xylanase-like protein OsXYN1 is required for normal cell wall deposition and plant development in rice

The rice (Oryza sativa) genome encodes 37 putative β-1,4-xylanase proteins, but none of them has been characterized at the genetic level. In this work, we report the isolation of slim stem (ss) mutants with pleiotropic defects, including dwarfism, leaf tip necrosis, and withered and rolled leaves under strong sunlight. Map-based cloning of the ss1 mutant identified the candidate gene as OsXyn1 (LOC_03g47010), which encodes a xylanase-like protein belonging to the glycoside hydrolase 10 (GH10) family. OsXyn1 was found to be widely expressed, especially in young tissues. Subcellular localization analysis showed that OsXyn1 encodes a membrane-associated protein. Physiological analysis of ss1 and the allelic ss2 mutant revealed that water uptake was partially compromised in these mutants. Consistently, the plant cell wall of the mutants exhibited middle lamella abnormalities or deficiencies. Immunogold assays revealed an unconfined distribution of xylan in the mutant cell walls, which may have contributed to a slower rate of plant cell wall biosynthesis and delayed plant growth. Additionally, water deficiency caused abscisic acid accumulation and triggered drought responses in the mutants. The findings that OsXyn1 is involved in plant cell wall deposition and the regulation of plant growth and development help to shed light on the functions of the rice GH10 family.

Evolutionary Understanding of Aquaporin Transport System in the Basal Eudicot Model Species Aquilegia coerulea

Aquaporins (AQPs) play a pivotal role in the cellular transport of water and many other small solutes, influencing many physiological and developmental processes in plants. In the present study, extensive bioinformatics analysis of AQPs was performed in Aquilegia coerulea L., a model species belonging to basal eudicots, with a particular focus on understanding the AQPs role in the developing petal nectar spur. A total of 29 AQPs were identified in Aquilegia, and their phylogenetic analysis performed with previously reported AQPs from rice, poplar and Arabidopsis depicted five distinct subfamilies of AQPs. Interestingly, comparative analysis revealed the loss of an uncharacterized intrinsic protein II (XIP-II) group in Aquilegia. The absence of the entire XIP subfamily has been reported in several previous studies, however, the loss of a single clade within the XIP family has not been characterized. Furthermore, protein structure analysis of AQPs was performed to understand pore diversity, which is helpful for the prediction of solute specificity. Similarly, an AQP AqcNIP2-1 was identified in Aquilegia, predicted as a silicon influx transporter based on the presence of features such as the G-S-G-R aromatic arginine selectivity filter, the spacing between asparagine-proline-alanine (NPA) motifs and pore morphology. RNA-seq analysis showed a high expression of tonoplast intrinsic proteins (TIPs) and plasma membrane intrinsic proteins (PIPs) in the developing petal spur. The results presented here will be helpful in understanding the AQP evolution in Aquilegia and their expression regulation, particularly during floral development.

Genome-wide identification and characterisation of Aquaporins in Nicotiana tabacum and their relationships with other Solanaceae species

BACKGROUND

Cellular membranes are dynamic structures, continuously adjusting their composition, allowing plants to respond to developmental signals, stresses, and changing environments. To facilitate transmembrane transport of substrates, plant membranes are embedded with both active and passive transporters. Aquaporins (AQPs) constitute a major family of membrane spanning channel proteins that selectively facilitate the passive bidirectional passage of substrates across biological membranes at an astonishing 108 molecules per second. AQPs are the most diversified in the plant kingdom, comprising of five major subfamilies that differ in temporal and spatial gene expression, subcellular protein localisation, substrate specificity, and post-translational regulatory mechanisms; collectively providing a dynamic transportation network spanning the entire plant. Plant AQPs can transport a range of solutes essential for numerous plant processes including, water relations, growth and development, stress responses, root nutrient uptake, and photosynthesis. The ability to manipulate AQPs towards improving plant productivity, is reliant on expanding our insight into the diversity and functional roles of AQPs.

RESULTS

We characterised the AQP family from Nicotiana tabacum (NtAQPs; tobacco), a popular model system capable of scaling from the laboratory to the field. Tobacco is closely related to major economic crops (e.g. tomato, potato, eggplant and peppers) and itself has new commercial applications. Tobacco harbours 76 AQPs making it the second largest characterised AQP family. These fall into five distinct subfamilies, for which we characterised phylogenetic relationships, gene structures, protein sequences, selectivity filter compositions, sub-cellular localisation, and tissue-specific expression. We also identified the AQPs from tobacco's parental genomes (N. sylvestris and N. tomentosiformis), allowing us to characterise the evolutionary history of the NtAQP family. Assigning orthology to tomato and potato AQPs allowed for cross-species comparisons of conservation in protein structures, gene expression, and potential physiological roles.

CONCLUSIONS

This study provides a comprehensive characterisation of the tobacco AQP family, and strengthens the current knowledge of AQP biology. The refined gene/protein models, tissue-specific expression analysis, and cross-species comparisons, provide valuable insight into the evolutionary history and likely physiological roles of NtAQPs and their Solanaceae orthologs. Collectively, these results will support future functional studies and help transfer basic research to applied agriculture.

The jasmonic acid pathway, rather than abscisic acid, may partly explain contrasting stomatal responses in two strawberry cultivars under osmotic stress

Drought is a major threat in agriculture and horticulture, including commercial strawberry production. Here, we compare hormonal regulation of a first-line drought stress response, namely stomatal closure, in two Fragaria x ananassa cultivars, known to differ in their drought stress phenotype. We show that the observed difference in xylem abscisic acid accumulation cannot explain the different stomatal responses under osmotic stress. Foliar abscisic acid accumulation cannot fully account for the stomatal behavior in one of both cultivars either. An indirect effect of abscisic acid on stomatal conductance via an impact on leaf hydraulic conductance, possibly mediated via aquaporins, as is recently proposed in literature, was not observed here. Next, we show that these two cultivars respond differently to jasmonic acid and one of its precursors. This difference in sensitivity of the jasmonates pathway between both cultivars may partly explain the different stomatal response. This study contributes to the understanding of the regulation of an important drought stress response in an economically important crop prone to water deficit stress.

Should Root Plasticity Be a Crop Breeding Target?

Root phenotypic plasticity has been proposed as a target for the development of more productive crops in variable environments. However, the plasticity of root anatomical and architectural responses to environmental cues is highly complex, and the consequences of these responses for plant fitness are poorly understood. We propose that root phenotypic plasticity may be beneficial in natural or low-input systems in which the availability of soil resources is spatiotemporally dynamic. Crop ancestors and landraces were selected with multiple stresses, competition, significant root loss and heterogenous resource distribution which favored plasticity in response to resource availability. However, in high-input agroecosystems, the value of phenotypic plasticity is unclear, since human management has removed many of these constraints to root function. Further research is needed to understand the fitness landscape of plastic responses including understanding the value of plasticity in different environments, environmental signals that induce plastic responses, and the genetic architecture of plasticity before it is widely adopted in breeding programs. Phenotypic plasticity has many potential ecological, and physiological benefits, but its costs and adaptive value in high-input agricultural systems is poorly understood and merits further research.

CO2 enrichment enhanced drought resistance by regulating growth, hydraulic conductivity and phytohormone contents in the root of cucumber seedlings

The coordinated effects of CO2 enrichment and drought stress on cucumber leaves have attracted increasing research attention, but few studies have investigated the effects of CO2 enrichment on the root system under drought stress. So we analyzed the morphological parameters, hydraulic conductivity, aquaporin-related gene expression, and endogenous phytohormone contents in roots of cucumber seedlings cultured under different CO2 concentrations (approximately 400 and 800 ± 40 μmol mol-1) and drought stresses simulated by polyethylene glycol 6000 (0%, 5%, and 10%). The results showed that under drought stress, regardless of the CO2 concentration, the root biomass and hydraulic conductivity decreased, the contents of auxin (IAA), zeatin nucleoside (ZR), and gibberellin (GA) decreased, the abscisic acid (ABA) content and the transcript levels of the aquaporin-related genes CsPIP2-4 increased, and the transcript levels of the aquaporin-related genes CsPIP2-5 and CsPIP2-7 decreased compared with no drought stress. Under moderate drought stress, CO2 enrichment decreased ABA content and the transcript level of CsPIP2-4, increased root biomass and GA content and the transcript level of CsPIP2-7, improved contribution rate of cell-to-cell water transport (mediated by aquaporins) and roots hydraulic conductivity. In summary, drought stress changed the water transport capacity of the roots and inhibited the growth of cucumber seedlings. CO2 enrichment regulated phytohormone contents and aquaporin-related gene expression, maintained the normal contribution rate of cell-to-cell water transport, and improved the root biomass and hydraulic conductivity, thereby alleviated the negative effects of drought stress on cucumber seedlings.

Improving water use efficiency by changing hydraulic and stomatal characteristics in soybean exposed to drought: the involvement of nitric oxide

A variety of cellular responses is needed to ensure the plants survival during drought, but little is known about the signaling mechanisms involved in this process. Soybean cultivars (EMBRAPA 48 and BR 16, tolerant and sensitive to drought, respectively) were exposed to the following treatments: control conditions (plants in field capacity), drought (20% of available water in the soil), sodium nitroprusside (SNP) treatment (plants irrigated and treated with 100-µM SNP [SNP-nitric oxide (NO) donor molecule], and Drought + SNP (plants subjected to drought and SNP treatment). Plants remained in these conditions until the reproductive stage and were evaluated for physiological (photosynthetic pigments, chlorophyll a fluorescence and gas exchange rates), hydraulic (water potential, osmotic potential and leaf hydraulic conductivity) and morpho-anatomical traits (biomass, venation density and stomatal characterization). Exposure to water deficit considerably reduced water potential in both cultivars and resulted in decrease in photosynthesis and biomass accumulation. The addition of the NO donor attenuated these damaging effects of water deficit and increased the tolerance index of both cultivars. The results showed that NO was able to reduce plant's water loss, while maintaining their biomass production through alteration in stomatal characteristics, hydraulic conductivity and the biomass distribution pattern. These hydraulic and morpho-anatomical alterations allowed the plants to obtain, transport and lose less water to the atmosphere, even in water deficit conditions.

Genetic control of root anatomical plasticity in maize

Root anatomical phenes have important roles in soil resource capture and plant performance; however, their phenotypic plasticity and genetic architecture is poorly understood. We hypothesized that (a) the responses of root anatomical phenes to water deficit (stress plasticity) and different environmental conditions (environmental plasticity) are genetically controlled and (b) stress and environmental plasticity are associated with different genetic loci than those controlling the expression of phenes under water-stress and well-watered conditions. Root anatomy was phenotyped in a large maize (Zea mays L.) association panel in the field with and without water deficit stress in Arizona and without water deficit stress in South Africa. Anatomical phenes displayed stress and environmental plasticity; many phenotypic responses to water deficit were adaptive, and the magnitude of response varied by genotype. We identified 57 candidate genes associated with stress and environmental plasticity and 64 candidate genes associated with phenes under well-watered and water-stress conditions in Arizona and under well-watered conditions in South Africa. Four candidate genes co-localized between plasticity groups or for phenes expressed under each condition. The genetic architecture of phenotypic plasticity is highly quantitative, and many distinct genes control plasticity in response to water deficit and different environments, which poses a challenge for breeding programs.

Drought tolerance of the grapevine, Vitis champinii cv. Ramsey, is associated with higher photosynthesis and greater transcriptomic responsiveness of abscisic acid biosynthesis and signaling

BACKGROUND

Grapevine is an economically important crop for which yield and berry quality is strongly affected by climate change. Large variations in drought tolerance exist across Vitis species. Some of these species are used as rootstock to enhance abiotic and biotic stress tolerance. In this study, we investigated the physiological and transcriptomic responses to water deficit of four different genotypes that differ in drought tolerance: Ramsey (Vitis champinii), Riparia Gloire (Vitis riparia), Cabernet Sauvignon (Vitis vinifera), and SC2 (Vitis vinifera x Vitis girdiana).

RESULTS

Ramsey was particularly more drought tolerant than the other three genotypes. Ramsey maintained a higher stomatal conductance and photosynthesis at equivalent levels of moderate water deficit. We identified specific and common transcriptomic responses shared among the four different Vitis species using RNA sequencing analysis. A weighted gene co-expression analysis identified a water deficit core gene set with the ABA biosynthesis and signaling genes, NCED3, RD29B and ABI1 as potential hub genes. The transcript abundance of many abscisic acid metabolism and signaling genes was strongly increased by water deficit along with genes associated with lipid metabolism, galactinol synthases and MIP family proteins. This response occurred at smaller water deficits in Ramsey and with higher transcript abundance than the other genotypes. A number of aquaporin genes displayed differential and unique responses to water deficit in Ramsey leaves. Genes involved in cysteine biosynthesis and metabolism were constitutively higher in the roots of Ramsey; thus, linking the gene expression of a known factor that influences ABA biosynthesis to this genotype's increased NCED3 transcript abundance.

CONCLUSION

The drought tolerant Ramsey maintained higher photosynthesis at equivalent water deficit than the three other grapevine genotypes. Ramsey was more responsive to water deficit; its transcriptome responded at smaller water deficits, whereas the other genotypes did not respond until more severe water deficits were reached. There was a common core gene network responding to water deficit for all genotypes that included ABA metabolism and signaling. The gene clusters and sub-networks identified in this work represent interesting gene lists to explore and to better understand drought tolerance molecular mechanisms.

Nitric oxide and hydrogen sulfide crosstalk during heavy metal stress in plants

Gases such as ethylene, hydrogen peroxide (H₂ O₂ ), nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂ S) have been recognized as vital signaling molecules in plants and animals. Of these gasotransmitters, NO and H₂ S have recently gained momentum mainly because of their involvement in numerous cellular processes. It is therefore important to study their various attributes including their biosynthetic and signaling pathways. The present review provides an insight into various routes for the biosynthesis of NO and H₂ S as well as their signaling role in plant cells under different conditions, more particularly under heavy metal stress. Their beneficial roles in the plant's protection against abiotic and biotic stresses as well as their adverse effects have been addressed. This review describes how H₂ S and NO, being very small-sized molecules, can quickly pass through the cell membranes and trigger a multitude of responses to various factors, notably to various stress conditions such as drought, heat, osmotic, heavy metal and multiple biotic stresses. The versatile interactions between H₂ S and NO involved in the different molecular pathways have been discussed. In addition to the signaling role of H₂ S and NO, their direct role in posttranslational modifications is also considered. The information provided here will be helpful to better understand the multifaceted roles of H₂ S and NO in plants, particularly under stress conditions.

Fungal Aquaporins in Ectomycorrhizal Root Water Transport

Ectomycorrhizal fungi influence root water transport of host plants. To delineate the exact mechanisms of how fungal partner alters root water relations, it is important to understand the functions of fungal transmembrane water channels, i.e., aquaporins, the key component in the symplastic pathways. In this paper, we discussed what roles the fungal aquaporins may play in root water transport. We also highlighted the opportunities of using integrated approaches to address rising questions in future hotspots of aquaporin and root water relations research.

Physiological responses and aquaporin expression upon drought and osmotic stress in a conservative vs prodigal Fragaria x ananassa cultivar

In order to improve the understanding of plant water relations under drought stress, the water use behavior of two Fragaria x ananassa Duch. cultivars, contrasting in their drought stress phenotype, is identified. Under drought, stomatal closure is gradual in Figaro. Based on this, we associate Figaro with conservative water use behavior. Contrarily, drought stress causes a sudden and steep decrease in stomatal conductance in Flair, leading to the identification of Flair as a prodigal water use behavior cultivar. Responses to progressive drought on the one hand and an osmotic shock on the other hand are compared between these two cultivars. Tonoplast intrinsic protein mRNA levels are shown to be upregulated under progressive drought in the roots of Figaro only. Otherwise, aquaporin expression upon drought or osmotic stress is similar between both cultivars, i.e. plasma membrane intrinsic proteins are downregulated under progressive drought in leaves and under short term osmotic shock in roots. In response to osmotic shock, root hydraulic conductivity did not change significantly and stomatal closure is equal in both cultivars. De novo abscisic acid biosynthesis is upregulated in the roots of both cultivars under progressive drought.

Local root ABA/cytokinin status and aquaporins regulate poplar responses to mild drought stress independently of the ectomycorrhizal fungus Laccaria bicolor

The relatively better performance of mycorrhizal plants subjected to drought stress has commonly been linked to improved root water uptake through the fungal regulation of plant aquaporins and hormones. In this study, we examined the role of ectomycorrhizal fungi in plant water relations and plant hormonal balance under mild drought using split-root seedlings of Populus trichocarpa × deltoides either with or without inoculation with Laccaria bicolor. The root compartments where the drought treatment was applied had higher ABA and lower cytokinin tZR contents, and greater expression of the plant aquaporins PtPIP1;1, PtPIP1;2, PtPIP2;5, and PtPIP2;7. On the other hand, the presence of L. bicolor within the roots down-regulated PtPIP1;4, PtPIP2;3, and PtPIP2;10, and reduced the abundance of PIP2 proteins. In addition, expression of the fungal aquaporins JQ585595 and JQ585596 were positively correlated with root ABA content, while tZR content was positively correlated with PtPIP1;4 and negatively correlated with PtPIP2;7. The results demonstrate a coordinated plant-fungal system that regulates the different mechanisms involved in water uptake in ectomycorrhizal poplar plants.

Genome Editing in Plants: Exploration of Technological Advancements and Challenges

Genome-editing, a recent technological advancement in the field of life sciences, is one of the great examples of techniques used to explore the understanding of the biological phenomenon. Besides having different site-directed nucleases for genome editing over a decade ago, the CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) based genome editing approach has become a choice of technique due to its simplicity, ease of access, cost, and flexibility. In the present review, several CRISPR/Cas based approaches have been discussed, considering recent advances and challenges to implicate those in the crop improvement programs. Successful examples where CRISPR/Cas approach has been used to improve the biotic and abiotic stress tolerance, and traits related to yield and plant architecture have been discussed. The review highlights the challenges to implement the genome editing in polyploid crop plants like wheat, canola, and sugarcane. Challenges for plants difficult to transform and germline-specific gene expression have been discussed. We have also discussed the notable progress with multi-target editing approaches based on polycistronic tRNA processing, Csy4 endoribonuclease, intron processing, and Drosha ribonuclease. Potential to edit multiple targets simultaneously makes it possible to take up more challenging tasks required to engineer desired crop plants. Similarly, advances like precision gene editing, promoter bashing, and methylome-editing will also be discussed. The present review also provides a catalog of available computational tools and servers facilitating designing of guide-RNA targets, construct designs, and data analysis. The information provided here will be useful for the efficient exploration of technological advances in genome editing field for the crop improvement programs.

Insights into the role of phytohormones regulating pAtNIP5;1 activity and boron transport in Arabidopsis thaliana

Aiming to counteract B deficiency impacts, plants have developed different strategies in order to reach an optimal growth in soils with limited B availability. These include B transport mechanisms that involves a facilitated transport, via channel proteins, and a high-affinity active transport driven by borate transporters. The AtNIP5;1 channel protein is a member of Major Intrinsic Protein family which facilitates B influx into the roots under low B supply. In order to explore the phytohormone-dependent regulation of AtNIP5;1, the effects of abscisic acid (ABA), ethylene, auxins and cytokinins on the activity of AtNIP5;1 promoter were evaluated using the reporter line pNIP5;1-GUS. The results show that ABA treatment increased pAtNIP5;1 activity. Besides, a larger B uptake was found following ABA treatment under B deficiency suggesting a role of ABA inducing B uptake. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) caused an induction of AtNIP5;1 expression although did not correlate with higher B concentrations nor with an improvement in root growth. On the contrary, auxins and cytokinins caused slight changes in pAtNIP5;1 induction. Altogether, these results show a regulatory role of phytohormones in AtNIP5;1 promoter what may affect B transport. The herein provided information may contribute to better understand the regulation of B transport in plants towards minimizing B deficiency impacts on agriculture.

Genome-wide analysis of the cotton G-coupled receptor proteins (GPCR) and functional analysis of GTOM1, a novel cotton GPCR gene under drought and cold stress

BACKGROUND

The efficient detection and initiation of appropriate response to abiotic stresses are important to plants survival. The plant G-protein coupled receptors (GPCRs) are diverse membranous proteins that are responsible for signal transduction.

RESULTS

In this research work, we identified a novel gene of the GPCR domain, transformed and carried out the functional analysis in Arabidopsis under drought and cold stresses. The transgenic lines exposed to drought and cold stress conditions showed higher germination rate, increased root length and higher fresh biomass accumulation. Besides, the levels of antioxidant enzymes, glutathione (GSH) and ascorbate peroxidase (APX) exhibited continuously increasing trends, with approximately threefold higher than the control, implying that these ROS-scavenging enzymes were responsible for the detoxification of ROS induced by drought and cold stresses. Similarly, the transgenic lines exhibited stable cell membrane stability (CMS), reduced water loss rate in the detached leaves and significant values for the saturated leaves compared to the wild types. Highly stress-responsive miRNAs were found to be targeted by the novel gene and based on GO analysis; the protein encoded by the gene was responsible for maintaining an integral component of membrane. In cotton, the virus-induced gene silencing (VIGS) plants exhibited a higher susceptibility to drought and cold stresses compared to the wild types.

CONCLUSION

The novel GPCR gene enhanced drought and cold stress tolerance in transgenic Arabidopsis plants by promoting root growth and induction of ROS scavenging enzymes. The outcome showed that the gene had a role in enhancing drought and cold stress tolerance, and can be further exploited in breeding for more stress-resilient and tolerant crops.

Genome-wide identification, structure characterization, and expression pattern profiling of aquaporin gene family in cucumber

BACKGROUND

Aquaporin (AQP) proteins comprise a group of membrane intrinsic proteins (MIPs) that are responsible for transporting water and other small molecules, which is crucial for plant survival under stress conditions including salt stress. Despite the vital role of AQPs, little is known about them in cucumber (Cucumis sativus L.).

RESULTS

In this study, we identified 39 aquaporin-encoding genes in cucumber that were separated by phylogenetic analysis into five sub-families (PIP, TIP, NIP, SIP, and XIP). Their substrate specificity was then assessed based on key amino acid residues such as the aromatic/Arginine (ar/R) selectivity filter, Froger's positions, and specificity-determining positions. The putative cis-regulatory motifs available in the promoter region of each AQP gene were analyzed and results revealed that their promoter regions contain many abiotic related cis-regulatory elements. Furthermore, analysis of previously released RNA-seq data revealed tissue- and treatment-specific expression patterns of cucumber AQP genes (CsAQPs). Three aquaporins (CsTIP1;1, CsPIP2;4, and CsPIP1;2) were the most transcript abundance genes, with CsTIP1;1 showing the highest expression levels among all aquaporins. Subcellular localization analysis in Nicotiana benthamiana epidermal cells revealed the diverse and broad array of sub-cellular localizations of CsAQPs. We then performed RNA-seq to identify the expression pattern of CsAQPs under salt stress and found a general decreased expression level of root CsAQPs. Moreover, qRT-PCR revealed rapid changes in the expression levels of CsAQPs in response to diverse abiotic stresses including salt, polyethylene glycol (PEG)-6000, heat, and chilling stresses. Additionally, transient expression of AQPs in N. benthamiana increased leaf water loss rate, suggesting their potential roles in the regulation of plant water status under stress conditions.

CONCLUSIONS

Our results indicated that CsAQPs play important roles in response to salt stress. The genome-wide identification and primary function characterization of cucumber aquaporins provides insight to elucidate the complexity of the AQP gene family and their biological functions in cucumber.

Drought Stress Effects and Olive Tree Acclimation under a Changing Climate

Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor.

Distinct leaf transcriptomic response of water deficient Eucalyptus grandis submitted to potassium and sodium fertilization

While potassium fertilization increases growth yield in Brazilian eucalyptus plantations, it could also increase water requirements, making trees more vulnerable to drought. Sodium fertilization, which has been shown to promote eucalyptus growth compared to K-deficient trees, could partially mitigate this adverse effect of potassium. However, little is known about the influence of K and Na fertilization on the tree metabolic response to water deficit. The aim of the present study was thus to analyze the transcriptome of leaves sampled from Eucalyptus grandis trees subjected to 37% rainfall reduction, and fertilized with potassium (K), sodium (Na), compared to control trees (C). The multifactorial experiment was set up in a field with a throughfall exclusion system. Transcriptomic analysis was performed on leaves from two-year-old trees, and data analyzed using multifactorial statistical analysis and weighted gene co-expression network analysis (WGCNA). Significant sets of genes were seen to respond to rainfall reduction, in interaction with K or Na fertilization, or to fertilization only (regardless of the water supply regime). The genes were involved in stress signaling, primary and secondary metabolism, secondary cell wall formation and photosynthetic activity. Our focus on key genes related to cation transporters and aquaporins highlighted specific regulation of ion homeostasis, and plant adjustment to water deficit. While water availability significantly affects the transcriptomic response of eucalyptus species, this study points out that the transcriptomic response is highly dependent on the fertilization regime. Our study is based on the first large-scale field trial in a tropical region, specifically designed to study the interaction between water availability and nutrition in eucalyptus. To our knowledge, this is the first global transcriptomic analysis to compare the influence of K and Na fertilization on tree adaptive traits in water deficit conditions.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.