Intrinsic Membrane Proteins Research Articles

CsMYB96 confers resistance to water loss in citrus fruit by simultaneous regulation of water transport and wax biosynthesis.

A Citrus sinensis R2R3 MYB transcription factor (CsMYB96) has previously been shown to be strongly associated with the expression of many genes related to wax biosynthesis in the fruit. In this study, CsMYB96 was found to alleviate water loss by simultaneously regulating the expression of genes encoding plasma membrane intrinsic proteins (CsPIPs) and wax-related genes. Expression profiling indicated that CsPIP1;1 and CsPIP2;4 had high expression that was representative of other aquaporins, and they were down-regulated in the peel of post-harvest citrus fruit. CsPIP2;4 was further characterized as the predominant CsPIP, with high expression and high-water channel activity. Transient overexpression of CsPIP2;4 accelerated water loss in citrus fruit. In silico analysis further indicated that the expression of CsMYB96 had a significant negative correlation with that of CsPIPs. In vivo and in vitro experiments confirmed that CsMYB96 was able to directly repress the expression of CsPIPs. In addition, CsMYB96 was able to activate wax-related genes and promote wax biosynthesis for defense against water loss. Transient and stable overexpression of CsMYB96 reduced water loss from both citrus fruit and Arabidopsis.

The complex regulation of NIS expression and activity in thyroid and extrathyroidal tissues.

The sodium/iodide symporter (NIS) is an intrinsic plasma membrane protein that mediates active iodide transport into the thyroid gland and into several extrathyroidal tissues. NIS-mediated iodide uptake plays a pivotal role in the biosynthesis of thyroid hormones, of which iodide is an essential constituent. For 80 years, radioiodide has been used for the diagnosis and treatment of thyroid cancer, a successful theranostic agent that is extending its use to extrathyroidal malignancies. The purpose of this review is to focus on the most recent findings regarding the mechanisms that regulate NIS both in thyroid and extra-thyroidal tissues. Among other issues, we discuss the different transcriptional regulatory elements that govern NIS transcription in different tissues, the epigenetic modifications that regulate its expression, and the role that miRNAs play in fine-tuning NIS after being transcribed. A review on how hormones, cytokines, and iodide itself regulate NIS is provided. We also review the present stage of understanding NIS dysregulation in cancer, occupied mainly by convergent signaling pathways and by new insights in the route that NIS follows through different subcellular compartments to the plasma membrane. Furthermore, we cover NIS distribution and function in the increasing number of extrathyroidal tissues that express the symporter, as well as the role that NIS plays in tumor progression independently of its transport activity.

Biomimetic immunomodulation by crosstalk with nanoparticulate regulatory T cells

<h2>Summary</h2> Hyperactive immunity mediates the development and progression of various immuno-inflammatory diseases. However, the use of immunosuppressive or anti-inflammatory agents has been largely restricted either by off-target side effects or by individual interaction site. Here, we describe a biomimetic manipulation strategy for immunosuppression by crosstalk with regulatory T (Treg) cell membrane-coated nanoparticles. Due to the reservation of intrinsic membrane proteins and function from Treg cells, coated nanoparticles can directly interact with multifaceted overactive immune cells. By virtue of this unique characteristic, nanoparticulate Treg cells inhibit macrophage-osteoclast differentiation, the maturation of dendritic cells, and the activation of effector T cells. In both murine and canine models of periodontitis, these nanoparticles successfully suppress excessive immune responses, alleviating inflammation and curbing alveolar bone resorption. Our work reveals how dysregulated immune responses can be effectively manipulated by biomimetic immunomodulation and proposes the utilization of nanoparticulate Treg cells as a promising approach to treat immuno-inflammatory diseases.

Gene Frequency Shift in Relict Abies pinsapo Forests Associated with Drought-Induced Mortality: Preliminary Evidence of Local-Scale Divergent Selection

Current climate change constitutes a challenge for the survival of several drought-sensitive forests. The study of the genetic basis of adaptation offers a suitable way to understand how tree species may respond to future climatic conditions, as well as to design suitable conservation and management strategies. Here, we focus on selected genetic signatures of the drought-sensitive relict fir, Abies pinsapo Boiss. Field sampling of 156 individuals was performed in two elevation ecotones, characterized by widespread A. pinsapo decline and mortality. The DNA from dead trees was investigated and compared to living individuals, accounting for different ages and elevations. We studied the genes gated outwardly-rectifying K+ (GORK) channel and Plasma membrane Intrinsic Protein (PIP1) aquaporin, previously related to drought response in plant model species, to test whether drought was the main abiotic factor driving the decline of A. pinsapo forests. A combination of linear regression and factor models were used to test these selection signatures, as well as a fixation index (Fst), used here to analyze the genetic structure. The results were consistent among these approaches, supporting a statistically significant association of the GORK gene with survival in one of the A. pinsapo populations. These results provide preliminary evidence for the potential role of the GORK gene in the resilience to drought of A. pinsapo.

Saussurea involucrata PIP2;7 improves photosynthesis and drought resistance by decreasing the stomatal density and increasing intracellular osmotic pressure

Aquaporin proteins are very important for water transport across the plasma membrane. In this study, the plasma membrane intrinsic protein PIP2;7 cloned from Saussurea involucrata was overexpressed in Arabidopsis thaliana. Transgenic lines showed rapid growth, with increased leaf numbers and leaf sizes, due to high rates of photosynthesis, transpiration, and stomatal conductance. Moreover, SiPIP2;7 conferred drought resistance in Arabidopsis by improving water use efficiency and intracellular osmotic pressure via a decrease in the stomatal density and increases in intracellular Cl−. These phenotypes were attributed to the effects of SiPIP2;7 on the relative expression levels of target genes related to the stomatal development and ion transport. Moreover, SiPIP2;7 gene improve drought resistance and fruit yield of tomato. These results indicated that the SiPIP2;7 gene is effective for breeding new varieties with high drought resistance and yield.

Mesophyll conductance variability of rice aquaporin knockout lines at different growth stages and growing environments.

The plasma membrane subfamily of aquaporins [plasma membrane intrinsic proteins (PIPs)], which facilitates the CO2 diffusion across membranes, is proposed to play an important role in mesophyll conductance to CO2 (gm ), a major limiting factor of photosynthesis. However, recent studies implied no causal relationship between gm and PIPs because they failed to repeat the previous observed differences in gm between PIP knockout lines and their wild-type. The contrasting results on the role of PIPs in gm were interpreted as the different growth conditions among studies, which has never been tested. Here, we assessed whether the differences in gm between wild-type and PIP knockout lines, Ospip1;1, Ospip1;2 and Ospip2;1, varied with growth condition (field versus pot condition) and growth stages in rice. Under field conditions, no differences were observed in plant performance, photosynthetic rate (A) and gm between PIP knockout lines and the wild-type. However, in agreement with previous studies, two out of three knockout lines showed significant declines in tiller number, plant height, A and gm under pot conditions. Moreover, we found that the differences in A and gm between PIP knockout lines and the wild-type varied with the growth stage of the plants. Our results showed that the differences in gm between PIP knockout lines and wild-type were depending on the growth environments and stage of the plants, and further efforts are required to reveal the underlying mechanisms.

Rice aquaporin OsPIP2;2 is a water-transporting facilitator in relevance to drought-tolerant responses.

In rice (Oryza sativa), the PLASMA MEMBRANE INTRINSIC PROTEIN (PIP) family of aquaporin has 11 members, OsPIP1;1 to OsPIP1;3, and OsPIP2;1 to OsPIP2;8, which are hypothesized to facilitate the transport of H2O and other small compounds across cell membranes. To date, however, only OsPIP1;2, OsPIP2;1, and OsPIP2;4 have been demonstrated for substrate selectivity in their source plant (rice). In this study, OsPIP2;2 was characterized as the most efficient facilitator of H2O transport across cell membranes in comparison with the other 10 OsPIPs. In concomitant tests of all OsPIPs, four genes (OsPIP1;3, OsPIP2;1, OsPIP2;2, and OsPIP2;4) were induced to express in leaves of rice plants following a physiological drought stress, while OsPIP2;2 was expressed to the highest level. After de novo expression in frog oocytes and yeast cells, the four OsPIP proteins were localized to the plasma membranes in trimer and tetramer and displayed the activity to increase the membrane permeability to H2O. In comparison, OsPIP2;2 was most supportive to H2O import to oocytes and yeast cells. After de novo expression in tobacco protoplasts, OsPIP2;2 exceeded OsPIP1;3, OsPIP2;1, and OsPIP2;4 to support H2O transport across the plasma membranes. OsPIP2;2‐mediated H2O transport was accompanied by drought‐tolerant responses, including increases in concentrations of proline and polyamines, both of which are physiological markers of drought tolerance. In rice protoplasts, H2O transport and drought‐tolerant responses, which included expression of marker genes of drought tolerance pathway, were considerably enhanced by OsPIP2;2 overexpression but strongly inhibited by the gene silencing. Furthermore, OsPIP2;2 played a role in maintenance of the cell membrane integrity and effectively protected rice cells from electrolyte leakage caused by the physiological drought stress. These results suggest that OsPIP2;2 is a predominant facilitator of H2O transport in relevance to drought tolerance in the plant.

Endogenous phytosulfokine α (PSKα) signaling delays petals senescence and prolongs vase life of cut rose flowers (Rosa hybrida cv. Angelina)

This study investigated the endogenous phytosulfokine α (PSKα) signaling during opening and senescence in rose flowers. Our results showed that the higher phytosulfokines (PSKs) and tyrosyl protein sulfotransferase (TPST) expression could be responsible for higher endogenous PSKα accumulation in petals during rose flowers opening (stages 2 and 3). By triggering the endogenous PSKα signaling, higher phytosulfokine receptor 1 (PSKR1) expression could be responsible for higher cytosolic cyclic guanosine monophosphate (cGMP) accumulation in petals during rose flowers opening (stages 3 and 4). Higher protein kinase G (PKG) and cyclic nucleotide-gated ion channel 1 (CNGC1) expression accompanying higher plasma membrane intrinsic protein 2 (PIP2) and tonoplast intrinsic protein 1 (TIP1) expression in petals during rose flowers opening may arise from higher cytosolic cGMP accumulation giving rise to higher petals relative water content (RWC) (stage 4). Triggering phosphodiesterase (PDE) expression lay off cytosolic cGMP signaling. Suppressing PKG and CNGC1 expression accompanying lower PIP2 and TIP1 expression accelerates petals senescence in rose flowers representing by deteriorating petals membrane integrity revealed by higher electrolyte leakage and malondialdehyde (MDA) accumulation (stage 5 and 6). For delaying petals senescence and prolonging vase life in cut rose flowers, we employed exogenous PSKα treatment at the commercial harvest stage (stage 3). Our results showed that the suppressing PDE expression in petals by exogenous 150 nM PSKα treatment could be responsible for allowing cytosolic cGMP signaling ongoing for supporting PKG and CNGC1 expression accompanying by higher PIP2 and TIP1 expression. Exogenous 150 nM PSKα treatment, outperforming cut rose flowers by delayed senescence and prolonged vase life to 16 days from 12 days could be ascribed to preserving membrane integrity revealed by lower electrolyte leakage and MDA accumulation. Our results could be proposed that exogenous PSKα treatment and endogenous PSKα signaling for employing in the floriculture industry for delaying petals senescence and prolonging the vase life of cut rose flower.

Genome-wide identification and expression analysis of aquaporin family in Canavalia rosea and their roles in the adaptation to saline-alkaline soils and drought stress

BackgroundCanavalia rosea (Sw.) DC. (bay bean) is an extremophile halophyte that is widely distributed in coastal areas of the tropics and subtropics. Seawater and drought tolerance in this species may be facilitated by aquaporins (AQPs), channel proteins that transport water and small molecules across cell membranes and thereby maintain cellular water homeostasis in the face of abiotic stress. In C. rosea, AQP diversity, protein features, and their biological functions are still largely unknown.ResultsWe describe the action of AQPs in C. rosea using evolutionary analyses coupled with promoter and expression analyses. A total of 37 AQPs were identified in the C. rosea genome and classified into five subgroups: 11 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, 11 Nod26-like intrinsic proteins, 4 small and basic intrinsic proteins, and 1 X-intrinsic protein. Analysis of RNA-Seq data and targeted qPCR revealed organ-specific expression of aquaporin genes and the involvement of some AQP members in adaptation of C. rosea to extreme coral reef environments. We also analyzed C. rosea sequences for phylogeny reconstruction, protein modeling, cellular localizations, and promoter analysis. Furthermore, one of PIP1 gene, CrPIP1;5, was identified as functional using a yeast expression system and transgenic overexpression in Arabidopsis.ConclusionsOur results indicate that AQPs play an important role in C. rosea responses to saline-alkaline soils and drought stress. These findings not only increase our understanding of the role AQPs play in mediating C. rosea adaptation to extreme environments, but also improve our knowledge of plant aquaporin evolution more generally.

Genome-Wide Identification, Structure Characterization, and Expression Pattern Profiling of the Aquaporin Gene Family in Betula pendula.

Aquaporin water channels (AQPs) constitute a large family of transmembrane proteins present throughout all kingdoms of life. They play key roles in the flux of water and many solutes across the membranes. The AQP diversity, protein features, and biological functions of silver birch are still unknown. A genome analysis of Betula pendula identified 33 putative genes encoding full-length AQP sequences (BpeAQPs). They are grouped into five subfamilies, representing ten plasma membrane intrinsic proteins (PIPs), eight tonoplast intrinsic proteins (TIPs), eight NOD26-like intrinsic proteins (NIPs), four X intrinsic proteins (XIPs), and three small basic intrinsic proteins (SIPs). The BpeAQP gene structure is conserved within each subfamily, with exon numbers ranging from one to five. The predictions of the aromatic/arginine selectivity filter (ar/R), Froger’s positions, specificity-determining positions, and 2D and 3D biochemical properties indicate noticeable transport specificities to various non-aqueous substrates between members and/or subfamilies. Nevertheless, overall, the BpePIPs display mostly hydrophilic ar/R selective filter and lining-pore residues, whereas the BpeTIP, BpeNIP, BpeSIP, and BpeXIP subfamilies mostly contain hydrophobic permeation signatures. Transcriptional expression analyses indicate that 23 BpeAQP genes are transcribed, including five organ-related expressions. Surprisingly, no significant transcriptional expression is monitored in leaves in response to cold stress (6 °C), although interesting trends can be distinguished and will be discussed, notably in relation to the plasticity of this pioneer species, B. pendula. The current study presents the first detailed genome-wide analysis of the AQP gene family in a Betulaceae species, and our results lay a foundation for a better understanding of the specific functions of the BpeAQP genes in the responses of the silver birch trees to cold stress.

Characterization of Interactions between the Soybean Salt-Stress Responsive Membrane-Intrinsic Proteins GmPIP1 and GmPIP2

Salt tolerance is an important trait in soybean cultivation and breeding. Plant responses to salt stress include physiological and biochemical changes that affect the movement of water across the plasma membrane. Plasma membrane intrinsic proteins (PIPs) localize to the plasma membrane and regulate the water and solutes flow. In this study, quantitative real-time PCR and yeast two-hybridization were engaged to analyze the early gene expression profiles and interactions of a set of soybean PIPs (GmPIPs) in response to salt stress. A total of 20 GmPIPs-encoding genes had varied expression profiles after salt stress. Among them, 13 genes exhibited a downregulated expression pattern, including GmPIP1;6, the constitutive overexpression of which could improve soybean salt tolerance, and its close homologs GmPIP1;7 and 1;5. Three genes showed upregulated patterns, including the GmPIP1;6 close homolog GmPIP1;4, when four genes with earlier increased and then decreased expression patterns. GmPIP1;5 and GmPIP1;6 could both physically interact strongly with GmPIP2;2, GmPIP2;4, GmPIP2;6, GmPIP2;8, GmPIP2;9, GmPIP2;11, and GmPIP2;13. Definite interactions between GmPIP1;6 and GmPIP1;7 were detected and GmPIP2;9 performed homo-interaction. The interactions of GmPIP1;5 with GmPIP2;11 and 2;13, GmPIP1;6 with GmPIP2;9, 2;11 and GmPIP2;13, and GmPIP2;9 with itself were strengthened upon salt stress rather than osmotic stress. Taken together, we inferred that GmPIP1 type and GmPIP2 type could associate with each other to synergistically function in the plant cell; a salt-stress environment could promote part of their interactions. This result provided new clues to further understand the soybean PIP–isoform interactions, which lead to potentially functional homo- and heterotetramers for salt tolerance.

A bamboo leaf-specific aquaporin gene PePIP2;7 is involved in abiotic stress response

PePIP2;7, a leaf-specific aquaporin gene in bamboo, is upregulated under abiotic stresses. Overexpressing PePIP2;7 confers abiotic stresses tolerance in transgenic Arabidopsis plant and yeast. Aquaporins (AQPs) participate in the regulation of water balance in plants. However, the function of AQPs in bamboo remains unclear. Here, PePIP2;7 was identified as a leaf-specific aquaporin gene in moso bamboo based on the expression analysis of transcriptome data and PCR. In situ hybridization further indicated that PePIP2;7 was mainly expressed in mesophyll cells of mature leaves, while in immature leaves it was dominant in blade edge cells followed by mesophyll cells. Interestingly, PePIP2;7 was strongly expressed in the mesophyll cells near bulliform cells of immature leaves, suggesting that PePIP2;7 might function in water transport and contribute to leaf unfolding. The transient expression assay showed that PePIP2;7 was a plasma membrane intrinsic protein. Furthermore, PePIP2;7 was upregulated under abiotic stresses such as high light, drought, and NaCl. Compared with Col-0, transgenic Arabidopsis plants overexpressing PePIP2;7 had better seed germination rate, longer taproot length, higher SOD activity, and lower MDA content under abiotic stresses. Besides, yeasts expressing PePIP2;7 also had higher tolerance to stress compared to the control. Taken together, our results show that PePIP2;7 is leaf-specific and involved in stress response, which provides new insights into aquaporin function in bamboo.

Poplar aquaporin PIP1;1 promotes Arabidopsis growth and development

BackgroundRoot hydraulic conductance is primarily determined by the conductance of living tissues to radial water flow. Plasma membrane intrinsic proteins (PIPs) in root cortical cells are important for plants to take up water and are believed to be directly involved in cell growth.ResultsIn this study, we found that constitutive overexpression of the poplar root-specific gene PtoPIP1;1 in Arabidopsis accelerated bolting and flowering. At the early stage of the developmental process, PtoPIP1;1 OE Arabidopsis exhibited faster cell growth in both leaves and roots. The turgor pressure of plants was correspondingly increased in PtoPIP1;1 OE Arabidopsis, and the water status was changed. At the same time, the expression levels of flowering-related genes (CRY1, CRY2 and FCA) and hub genes in the regulatory networks underlying floral timing (FT and SOC1) were significantly upregulated in OE plants, while the floral repressor FLC gene was significantly downregulated.ConclusionsTaken together, the results of our study indicate that constitutive overexpression of PtoPIP1;1 in Arabidopsis accelerates bolting and flowering through faster cell growth in both the leaf and root at an early stage of the developmental process. The autonomous pathway of flowering regulation may be executed by monitoring developmental age. The increase in turgor and changes in water status with PtoPIP1;1 overexpression play a role in promoting cell growth.

Tolerance mechanisms in maize identified through phenotyping and transcriptome analysis in response to water deficit stress.

The online version contains supplementary material available at 10.1007/s12298-021-01003-4.

Editor’s Letter

<i>SLCO1B1 </i>(<i>solute carrier organic anion transporter family member 1B1</i>) is an important transmembrane hepatic uptake transporter. Genetic variants in the <i>SLCO1B1</i> gene have been associated with altered protein folding, resulting in protein degradation and decreased transporter activity. Next-generation sequencing (NGS) of pharmacogenes is being applied increasingly to associate variation in drug response with genetic sequence variants. However, it is difficult to link variants of unknown significance with functional phenotypes using “one-at-a-time” functional systems. Deep mutational scanning (DMS) using a “landing pad cell–based system” is a high-throughput technique designed to analyze hundreds of gene open reading frame (ORF) missense variants in a parallel and scalable fashion. We have applied DMS to analyze 137 missense variants in the <i>SLCO1B1</i> ORF obtained from the Exome Aggregation Consortium project. ORFs containing these variants were fused to green fluorescent protein and were integrated into “landing pad” cells. Florescence-activated cell sorting was performed to separate the cells into four groups based on fluorescence readout indicating protein expression at the single cell level. NGS was then performed and <i>SLCO1B1</i> variant frequencies were used to determine protein abundance. We found that six variants not previously characterized functionally displayed less than 25% and another 12 displayed approximately 50% of wild-type protein expression. These results were then functionally validated by transporter studies. Severely damaging variants identified by DMS may have clinical relevance for <i>SLCO1B1-</i>dependent drug transport, but we need to exercise caution since the relatively small number of severely damaging variants identified raise questions with regard to the application of DMS to intrinsic membrane proteins such as organic anion transporter protein 1B1. <h3>Significance Statement</h3> The functional implications of a large numbers of open reading frame (ORF) “variants of unknown significance” (VUS) in transporter genes have not been characterized. This study applied deep mutational scanning to determine the functional effects of VUS that have been observed in the ORF of <i>SLCO1B1</i>(<i>s</i><i>olute carrier organic anion transporter family member 1B1</i>). Several severely damaging variants were identified, studied, and validated. These observations have implications for both the application of deep mutational scanning to intrinsic membrane proteins and for the clinical effect of drugs and endogenous compounds transported by <i>SLCO1B1</i>.

Molecular insights into the role of plant transporters in salt stress response.

Salt stress disturbs the cellular osmotic and ionic balance, which then creates a negative impact on plant growth and development. The Na+ and Cl- ions can enter into plant cells through various membrane transporters, including specific and non-specific Na+ , K+ , and Ca2+ transporters. Therefore, it is important to understand Na+ and K+ transport mechanisms in plants along with the isolation of genes, their characterization, the structural features, and their post-translation regulation under salt stress. This review summarizes the molecular insights of plant ion transporters, including non-selective cation transporters, cyclic nucleotide-gated cation transporters, glutamate-like receptors, membrane intrinsic proteins, cation proton antiporters, and sodium proton antiporter families. Further, we discussed the K+ transporter families such as high-affinity K+ transporters, HAK/KUP/KT transporters, shaker type K+ transporters, and K+ efflux antiporters. Besides the ion transport process, we have shed light on available literature on epigenetic regulation of transport processes under salt stress. Recent advancements of salt stress sensing mechanisms and various salt sensors within signaling transduction pathways are discussed. Further, we have compiled salt-stress signaling pathways, and their crosstalk with phytohormones.

Elevated CO2 Modulates Plant Hydraulic Conductance Through Regulation of PIPs Under Progressive Soil Drying in Tomato Plants.

Increasing atmospheric CO2 concentrations accompanied by abiotic stresses challenge food production worldwide. Elevated CO2 (e[CO2]) affects plant water relations via multiple mechanisms involving abscisic acid (ABA). Here, two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (AC) and its ABA-deficient mutant (flacca), were used to investigate the responses of plant hydraulic conductance to e[CO2] and drought stress. Results showed that e[CO2] decreased transpiration rate (E) increased plant water use efficiency only in AC, whereas it increased daily plant water consumption and osmotic adjustment in both genotypes. Compared to growth at ambient [CO2], AC leaf and root hydraulic conductance (Kleaf and Kroot) decreased at e[CO2], which coincided with the transcriptional regulations of genes of plasma membrane intrinsic proteins (PIPs) and OPEN STOMATA 1 (OST1), and these effects were attenuated in flacca during soil drying. Severe drought stress could override the effects of e[CO2] on plant water relation characteristics. In both genotypes, drought stress resulted in decreased E, Kleaf, and Kroot accompanied by transcriptional responses of PIPs and OST1. However, under conditions combining e[CO2] and drought, some PIPs were not responsive to drought in AC, indicating that e[CO2] might disturb ABA-mediated drought responses. These results provide some new insights into mechanisms of plant hydraulic response to drought stress in a future CO2-enriched environment.

Ethylene enhances root water transport and aquaporin expression in trembling aspen (Populus tremuloides) exposed to root hypoxia

BackgroundRoot hypoxia has detrimental effects on physiological processes and growth in most plants. The effects of hypoxia can be partly alleviated by ethylene. However, the tolerance mechanisms contributing to the ethylene-mediated hypoxia tolerance in plants remain poorly understood.ResultsIn this study, we examined the effects of root hypoxia and exogenous ethylene treatments on leaf gas exchange, root hydraulic conductance, and the expression levels of several aquaporins of the plasma membrane intrinsic protein group (PIP) in trembling aspen (Populus tremuloides) seedlings. Ethylene enhanced net photosynthetic rates, transpiration rates, and root hydraulic conductance in hypoxic plants. Of the two subgroups of PIPs (PIP1 and PIP2), the protein abundance of PIP2s and the transcript abundance of PIP2;4 and PIP2;5 were higher in ethylene-treated trembling aspen roots compared with non-treated roots under hypoxia. The increases in the expression levels of these aquaporins could potentially facilitate root water transport. The enhanced root water transport by ethylene was likely responsible for the increase in leaf gas exchange of the hypoxic plants.ConclusionsExogenous ethylene enhanced root water transport and the expression levels of PIP2;4 and PIP2;5 in hypoxic roots of trembling aspen. The results suggest that ethylene facilitates the aquaporin-mediated water transport in plants exposed to root hypoxia.

Genome-wide identification, characterization of aquaporin gene family and understanding aquaporin transport system in hot pepper (Capsicum annuum L.)

The aquaporin gene family constitute essential channel proteins and is highly conserved which possess multiple functions all through plant growth, development and under stress conditions. They play a key role in transport of water and other solutes. In the present work, we report a comprehensive genome wide search for aquaporins in Capsicum annuum, a widely grown commercial crop. A total of fifty chilli aquaporins (CaAQPs) were identified and classified into five sub-families namely plasma membrane intrinsic proteins (PIPs), tonoplast intrinsic proteins (TIPs), NOD26-like intrinsic proteins (NIPs), small basic intrinsic proteins (SIPs) and xintrinsic proteins (XIPs) based on phylogenetic analysis. Functional prediction based on analysis of key amino acid residues viz., aromatic/arginine (ar/R) selectivity filter, Froger's Positions, Specificity Determining Positions demonstrated significant differences for substrate specificity among sub-families. Analysis of physical distribution of genes revealed uneven distribution of CaAQPs in genome. Drought induced expression pattern of CaAQPs, studied by qRT- PCR analysis illustrated varied and distinct expression profiles in various organs (leaves and roots) and between genotypes differing in drought tolerance. These results provide fundamental and indispensible insights into the role of the studied CaAQP genes under drought conditions. The present work contributes a reference and resource for further investigation of CaAQPs as candidate genes for genetic improvement studies of drought stress tolerance in hot pepper.

Aquaporins in Cereals-Important Players in Maintaining Cell Homeostasis under Abiotic Stress.

Cereal productivity is reduced by environmental stresses such as drought, heat, elevated CO2, salinity, metal toxicity and cold. Sometimes, plants are exposed to multiple stresses simultaneously. Plants must be able to make a rapid and adequate response to these environmental stimuli in order to restore their growing ability. The latest research has shown that aquaporins are important players in maintaining cell homeostasis under abiotic stress. Aquaporins are membrane intrinsic proteins (MIP) that form pores in the cellular membranes, which facilitate the movement of water and many other molecules such as ammonia, urea, CO2, micronutrients (silicon and boron), glycerol and reactive oxygen species (hydrogen peroxide) across the cell and intercellular compartments. The present review primarily focuses on the diversity of aquaporins in cereal species, their cellular and subcellular localisation, their expression and their functioning under abiotic stresses. Lastly, this review discusses the potential use of mutants and plants that overexpress the aquaporin-encoding genes to improve their tolerance to abiotic stress.