Aquaporin Gene Family Research Articles

Aquaporin (AQP) gene family in Buffalo and Goat: Molecular characterization and their expression analysis

Aquaporins (AQPs) are essential membrane proteins facilitating water and small solute transport across cell membranes. Mammals have approximately 13 paralogs of AQPs that may have evolved through gene duplication events. These genes are present in two separate clusters within the genome. In the present study, comprehensive 13 AQP genes (AQP0–12) were cloned and characterized in buffalo and goat. The protein coding region of AQPs in both species ranged from 729 to 990 bps, corresponding to 263–330 amino acid residues. Two important residues including NPA motifs and ar/R selectivity filter were found conserved in all AQPs, except for AQP7, 11 and 12. AQP0, 2, 4, 5, 7, 9, 12 showed tissue-restricted expression, whereas AQP1, 3, 8, and 11 exhibited ubiquitous expression across several tissues. AQP10 was identified as a pseudogene in all artiodactyls. Transcript variants were identified in buffalo and goat, where some variants of goat AQP5 and 6 lacked important motifs. Evolutionary analysis indicated positive selection at or near the NPA motifs and ar/R selectivity filter of AQP0, 3, 6, 7, and 10 that may alter its structure and function. This study is crucial for future investigations aiming to study the molecular mechanisms of AQPs in response to various physiological conditions.

Genome-Wide Analysis of Aquaporins Gene Family in Populus euphratica and Its Expression Patterns in Response to Drought, Salt Stress, and Phytohormones.

Aquaporins (AQPs) play an essential role in membrane water transport during plant responses to water stresses centered on conventional upstream signals. Phytohormones (PHs) regulate plant growth and yield, working with transcription factors to help plants withstand environmental challenges and regulate physiological and chemical processes. The AQP gene family is important, so researchers have studied its function and regulatory system in numerous species. Yet, there is a critical gap the understanding of many of their molecular features, thus our full knowledge of AQPs is far-off. In this study, we undertook a broad examination of the AQP family gene in Populus euphratica via bioinformatics tools and analyzed the expression patterns of certain members in response to drought, salt, and hormone stress. A total of 22 AQP genes were examined in P. euphratica, and were categorized into four main groups, including TIPs, PIPs, SIPs, and NIPs based on phylogenetic analysis. Comparable exon-intron gene structures were found by gene structure examination, and similarities in motif number and pattern within the same subgroup was determined by motif analysis. The PeuAQP gene family has numerous duplications, and there is a distinct disparity in how the members of the PeuAQP family react to post-translational modifications. Abiotic stress and hormone responses may be mediated by AQPs, as indicated by the abundance of stress response elements found in 22 AQP genes, as revealed by the promoter's cis-elements prediction. Expression pattern analysis reveals that selected six AQP genes from the PIP subgroup were all expressed in the leaves, stem, and roots with varying expression levels. Moreover, qRT-PCR analysis discovered that the majority of the selected AQP members were up- or down-regulated in response to hormone treatment and abiotic stress. Remarkably, PeuAQP14 and PeuAQP15 appeared to be highly responsive to drought stress and PeuAQP15 exhibited a high response to salt stress. The foliar application of the phytohormones (SA, IAA, GA3, MeJA, and ABA) were found to either activate or inhibit PeuAQP, suggesting that they may mitigate the effects of water shortage of poplar water stress. The present work enhances our knowledge of the practical roles of AQPs in stress reactions and offers fundamental information for the AQP genes in poplar species. It also highlights a direction for producing new varieties of poplar species with drought, salt, and hormone tolerance and holds substantial scientific and ecological importance, offering a potential contribution to the conservation of poplar species in arid regions.

Identification of Catalpa bungei Aquaporin Gene Family Related to Low Temperature Stress

Identification of Catalpa bungei Aquaporin Gene Family Related to Low Temperature Stress

Visual Analytics for Robust Investigations of Placental Aquaporin Gene Expression in Response to Maternal SARS-CoV-2 Infection

The human placenta is a multifunctional, disc-shaped temporary fetal organ that develops in the uterus during pregnancy, connecting the mother and the fetus. The availability of large-scale datasets on the gene expression of placental cell types and scholarly articles documenting adverse pregnancy outcomes from maternal infection warrants the use of computational resources to aid in knowledge generation from disparate data sources. Using maternal Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection as a case study in microbial infection, we constructed integrated datasets and implemented visual analytics resources to facilitate robust investigations of placental gene expression data in the dimensions of flow, curation, and analytics. The visual analytics resources and associated datasets can support a greater understanding of SARS-CoV-2-induced changes to the human placental expression levels of 18,882 protein-coding genes and at least 1233 human gene groups/families. We focus this report on the human aquaporin gene family that encodes small integral membrane proteins initially studied for their roles in water transport across cell membranes. Aquaporin-9 (AQP9) was the only aquaporin downregulated in term placental villi from SARS-CoV-2-positive mothers. Previous studies have found that (1) oxygen signaling modulates placental development; (2) oxygen tension could modulate AQP9 expression in the human placenta; and (3) SARS-CoV-2 can disrupt the formation of oxygen-carrying red blood cells in the placenta. Thus, future research could be performed on microbial infection-induced changes to (1) the placental hematopoietic stem and progenitor cells; and (2) placental expression of human aquaporin genes, especially AQP9.

Genome-wide analysis and expression of the aquaporin gene family in Avena sativa L.

Oat (Avena sativa L.) belongs to the early maturity grass subfamily of the Gramineae subfamily oats (Avena) and has excellent characteristics, such as tolerance to barrenness, salt, cold, and drought. Aquaporin (AQP) proteins belong to the major intrinsic protein (MIP) superfamily, are widely involved in plant growth and development, and play an important role in abiotic stress responses. To date, previous studies have not identified or analyzed the AsAQP gene family system, and functional studies of oat AQP genes in response to drought, cold, and salt stress have not been performed. In this study, AQP genes (AsAQP) were identified from the oat genome, and various bioinformatics data on the AQP gene family, gene structure, gene replication, promoters and regulatory networks were analyzed. Quantitative real-time PCR technology was used to verify the expression patterns of the AQP gene family in different oat tissues under different abiotic stresses. In this study, a total of 45 AQP genes (AsAQP) were identified from the oat reference genome. According to a phylogenetic analysis, 45 AsAQP were divided into 4 subfamilies (PIP, SIP, NIP, and TIP). Among the 45 AsAQP, 23 proteins had interactions, and among these, 5AG0000633.1 had the largest number of interacting proteins. The 20 AsAQP genes were expressed in all tissues, and their expression varied greatly among different tissues and organs. All 20 AsAQP genes responded to salt, drought and cold stress. The NIP subfamily 6Ag0000836.1 gene was significantly upregulated under different abiotic stresses and could be further verified as a key candidate gene. The findings of this study provide a comprehensive list of members and their sequence characteristics of the AsAQP protein family, laying a solid theoretical foundation for further functional analysis of AsAQP in oats. This research also offers valuable reference for the creation of stress-tolerant oat varieties through genetic engineering techniques.

Analysis of Carica papaya Informs Lineage-Specific Evolution of the Aquaporin (AQP) Family in Brassicales.

Aquaporins (AQPs), a type of intrinsic membrane proteins that transport water and small solutes across biological membranes, play crucial roles in plant growth and development. This study presents a first genome-wide identification and comparative analysis of the AQP gene family in papaya (Carica papaya L.), an economically and nutritionally important fruit tree of tropical and subtropical regions. A total of 29 CpAQP genes were identified, which represent five subfamilies, i.e., nine plasma intrinsic membrane proteins (PIPs), eight tonoplast intrinsic proteins (TIPs), seven NOD26-like intrinsic proteins (NIPs), two X intrinsic proteins (XIPs), and three small basic intrinsic proteins (SIPs). Although the family is smaller than the 35 members reported in Arabidopsis, it is highly diverse, and the presence of CpXIP genes as well as orthologs in Moringa oleifera and Bretschneidera sinensis implies that the complete loss of the XIP subfamily in Arabidopsis is lineage-specific, sometime after its split with papaya but before Brassicaceae-Cleomaceae divergence. Reciprocal best hit-based sequence comparison of 530 AQPs and synteny analyses revealed that CpAQP genes belong to 29 out of 61 identified orthogroups, and lineage-specific evolution was frequently observed in Brassicales. Significantly, the well-characterized NIP3 group was completely lost; lineage-specific loss of the NIP8 group in Brassicaceae occurred sometime before the divergence with Cleomaceae, and lineage-specific loss of NIP2 and SIP3 groups in Brassicaceae occurred sometime after the split with Cleomaceae. In contrast to a predominant role of recent whole-genome duplications (WGDs) on the family expansion in B. sinensis, Tarenaya hassleriana, and Brassicaceae plants, no recent AQP repeats were identified in papaya, and ancient WGD repeats are mainly confined to the PIP subfamily. Subfamily even group-specific evolution was uncovered via comparing exon-intron structures, conserved motifs, the aromatic/arginine selectivity filter, and gene expression profiles. Moreover, down-regulation during fruit ripening and expression divergence of duplicated CpAQP genes were frequently observed in papaya. These findings will not only improve our knowledge on lineage-specific family evolution in Brassicales, but also provide valuable information for further studies of AQP genes in papaya and species beyond.

Spatially resolved transcriptomic analysis of the germinating barley grain.

Seeds are a vital source of calories for humans and a unique stage in the life cycle of flowering plants. During seed germination, the embryo undergoes major developmental transitions to become a seedling. Studying gene expression in individual seed cell types has been challenging due to the lack of spatial information or low throughput of existing methods. To overcome these limitations, a spatial transcriptomics workflow was developed for germinating barley grain. This approach enabled high-throughput analysis of spatial gene expression, revealing specific spatial expression patterns of various functional gene categories at a sub-tissue level. This study revealed over 14000 genes differentially regulated during the first 24 hafter imbibition. Individual genes, such as the aquaporin gene family, starch degradation, cell wall modification, transport processes, ribosomal proteins and transcription factors, were found to have specific spatial expression patterns over time. Using spatial autocorrelation algorithms, we identified auxin transport genes that had increasingly focused expression within subdomains of the embryo over time, suggesting their role in establishing the embryo axis. Overall, our study provides an unprecedented spatially resolved cellular map for barley germination and identifies specific functional genomics targets to better understand cellular restricted processes during germination. The data can be viewed at https://spatial.latrobe.edu.au/.

Evolution and phylogenetic diversity of the aquaporin gene family in arachnids

Water flux across cells predominantly occurs through the pore formed by the aquaporin channels. Since water balance is one of the most important challenges to terrestrial animals, aquaporin evolution and diversity is known to play roles in animal terrestrialisation. Arachnids (Arthropoda: Chelicerata: Arachnida) are the second most diverse group and represent the pioneer land colonists in animals; however, there remains no thorough investigation on aquaporin evolution and diversity in this evolutionarily important lineage. Here we reported a phylogenetic study of aquaporin evolution and diversity using genomic data from 116 arachnid species covering almost all (15/16) extant orders. A previously unrecognised subfamily related to aquaporin-4 (i.e. Aqp4-like subfamily) via phylogenetic analysis was identified, suggesting certain underestimate of the arachnid aquaporin diversity in earlier studies probably due to limited taxonomic sampling. Further analysis indicates that this subfamily emerged deep within the life tree of arthropods. Gene tree of another Aqp4-like subfamily (PripL) shows an unexpected basal split between acariform mites (Acariformes) and other arachnids. A closer inspection demonstrated that the PripL evolved quickly and has been under differential selection pressure in acariform mites. Evidence is provided that the evolutionarily ancient Glp subfamily (i.e. aquaglyceroporin) is significantly expanded in terrestrial arachnids compared with their marine relatives. Finally, in spite of the phylogenetic diversity, there exists conservation of some exons in size, functional domain, and intron-insertion phase: an 81-bp and a 218-bp exon, respectively, in apq4-like and glp genes across Eumetazoa lineages including arachnids and human beings. Both exons encode the carboxyl-terminal NPA motif, implying the coding and splicing pressure during hundreds of million years of animal evolution. Hypotheses were tested to explore the possible link between these findings and arachnid terrestrialisation.

Genome-wide identification, structural and evolutionary characteristics, and expression analysis of aquaporin gene family members in Mercenaria mercenaria

Aquaporins (AQPs) are highly-selective transmembrane water transporters that are involved in the adaptation to environmental challenges. However, the structure, function, and evolution of AQPs in bivalves remain largely unknown. In this study, AQP gene family members were identified in nine bivalve species, and their abundance rangs from 7 to 15. Nine AQPs (MmAQPs) were identified in the genome of hard clam (Mercenaria mercenaria), which is a euryhaline bivalve that has evolved sophisticated osmoregulatory mechanisms and salinity adaptation. Structurally, all MmAQPs contain 6 or 12 transmembrane α-helices, a major intrinsic protein (MIP) domain, and 2 asparagine-proline-alanine (NPA) motifs. MmAQPs were classified into three subfamilies based on phylogenetic analysis: AQP1-like, AQP3-like, and AQP8-like. No AQP11-like subfamily member was identified in the genome of hard clam. Tandem duplication resulted in a lineage-specific expansion in AQP8-like subfamily in hard clams. MmAQP8 genes showed different expression sensitivity to different environmental stressors. The gene expression patterns of three MmAQP8 were similar under heat, hypoxia, and air exposure stress, but differed greatly under salinity stress, indicating that tandem duplication events may accelerate the functional divergence of AQP8 genes in hard clams. AQP3-like members may have undergone gene loss during evolution, resulting in weakened glycerol and urea penetration in hard clams. Three orthologs of MmAQPs were detected in the genomes of Cyclina sinensis and Archivesica marissinica through synteny analyses. Tissue expression profiles showed that MmAQP genes were highly expressed in the foot and hepatopancreas. Under environmental stress, the expression levels of most of the MmAQP genes changed significantly to maintain metabolic homeostasis. Several MmAQP genes were downregulated to reduce water permeability under salinity and air exposure stress. Several MmAQP genes were significantly upregulated to promote the transmembrane transport of ammonia and reactive oxygen species and activate anti-apoptotic responses to resist stress. This study provides a comprehensive understanding of the AQP gene family in hard clams, and lays a foundation for further studies to explore the functions of AQPs in bivalves.

Function and evolution of the aquaporin IsAQP1 in the Lyme disease vector Ixodes scapularis.

Ticks are important vectors of pathogenic viruses, bacteria, and protozoans to humans, wildlife, and domestic animals. Due to their life cycles, ticks face significant challenges related to water homeostasis. When blood-feeding, they must excrete water and ions, but when off-host (for stretches lasting several months), they must conserve water to avoid desiccation. Aquaporins (AQPs), a family of membrane-bound water channels, are key players in osmoregulation in many animals but remain poorly characterized in ticks. Here, we bioinformatically identified AQP-like genes from the deer tick Ixodes scapularis and used phylogenetic approaches to map the evolution of the aquaporin gene family in arthropods. Most arachnid AQP-like sequences (including those of I.scapularis) formed a monophyletic group clustered within aquaglycerolporins (GLPs) from bacteria to vertebrates. This gene family is absent from insects, revealing divergent evolutionary paths for AQPs in different hematophagous arthropods. Next, we sequenced the full-length cDNA of I.scapularis aquaporin 1 (IsAQP1) and expressed it heterologously in Xenopus oocytes to functionally characterize its permeability to water and solutes. Additionally, we examined IsAQP1 expression across different life stages and adult female organs. We found IsAQP1 is an efficient water channel with high expression in salivary glands prior to feeding, suggesting it plays a role in osmoregulation before or during blood feeding. Its functional properties are unique: unlike most GLPs, IsAQP1 has low glycerol permeability, and unlike most AQPs, it is insensitive to mercury. Together, our results suggest IsAQP1 plays an important role in tick water balance physiology and that it may hold promise as a target of novel vector control efforts.

Genome-Wide Analysis of Aquaporin Gene Family in Triticum turgidum and Its Expression Profile in Response to Salt Stress.

During the response of plants to water stresses, aquaporin (AQP) plays a prominent role in membrane water transport based on the received upstream signals. Due to the importance of the AQP gene family, studies have been conducted that investigate the function and regulatory system of these genes. However, many of their molecular aspects are still unknown. This study aims to carry out a genome-wide investigation of the AQP gene family in Triticum turgidum using bioinformatics tools and to investigate the expression patterns of some members in response to salt stress. Our results show that there are 80 TtAQP genes in T. turgidum, which are classified into four main groups based on phylogenetic analysis. Several duplications were observed between the members of the TtAQP gene family, and high diversity in response to post-translational modifications was observed between TtAQP family members. The expression pattern of TtAQP genes disclosed that these genes are primarily upregulated in response to salt stress. Additionally, the qPCR data revealed that TtAQPs are more induced in delayed responses to salinity stress. Overall, our findings illustrate that TtAQP members are diverse in terms of their structure, regulatory systems, and expression levels.

Genome-Wide Identification and Expression Analysis of the Aquaporin Gene Family in Lycium barbarum during Fruit Ripening and Seedling Response to Heat Stress.

Plant-water relations mediated by aquaporins (AQPs) play vital roles in both key plant growth processes and responses to environmental challenges. As a well-known medicinal and edible plant, the harsh natural growth habitat endows Lycium plants with ideal materials for stress biology research. However, the details of their molecular switch for water transport remain unclear. In the present work, we first identified and characterized AQP family genes from Lycium (L.) barbarum at the genome scale and conducted systemic bioinformatics and expression analyses. The results showed that there were 38 Lycium barbarum AQPs (LbAQPs) in L. barbarum, which were classified into four subfamilies, including 17 LbPIP, 9 LbTIP, 10 LbNIP, and 2 LbXIP. Their encoded genes were unevenly distributed on all 12 chromosomes, except chromosome 10. Three of these genes encoded truncated proteins and three genes underwent clear gene duplication events. Cis-acting element analysis indicated that the expression of LbAQPs may be mainly regulated by biotic/abiotic stress, phytohormones and light. The qRT-PCR assay indicated that this family of genes presented a clear tissue-specific expression pattern, in which most of the genes had maximal transcript levels in roots, stems, and leaves, while there were relatively lower levels in flowers and fruits. Most of the LbAQP genes were downregulated during L. barbarum fruit ripening and presented a negative correlation with the fruit relative water content (RWC). Most of their transcripts presented a quick and sharp upregulation response to heat stress following exposure of the 2-month-old seedlings to a 42 °C temperature for 0, 1, 3, 12, or 24 h. Our results proposed that LbAQPs were involved in L. barbarum key development events and abiotic stress responses, which may lay a foundation for further studying the molecular mechanism of the water relationship of Lycium plants, especially in harsh environments.

Genome-wide identification and expression analysis of the aquaporin gene family reveals the role in the salinity adaptability in Nile tilapia (Oreochromis niloticus).

Nile tilapia (Oreochromis niloticus), an important economic freshwater fish being cultured globally, is highly adaptable to a wide range of salinities. However, little information is currently available on the mechanism of salinity adaptation. For a better understanding of this intriguing adaptability, we identified and analyzed aquaporins (AQPs), which are channel proteins with a basic function of intracellular and intercellular transportation for water and certain solutes. In the present study, we performed genome-wide identification and comprehensive analysis of the duplicated AQP genes in Nile tilapia by bioinformatics methods. Tissue-specific analyses were then combined with transcriptome data under different salinity treatments. It was revealed that Nile tilapia has a total of twenty-eight AQPs, which are distributed unevenly on twelve chromosomes and belong to four subfamilies according to phylogenetic analysis. These AQPs share conserved AQP characteristic structural domains and motifs, although they differ in molecular weight from 23 to 36kDa and contain distinct sequences. GO analysis revealed that most AQPs have transporter protein activity and are involved in biological processes such as substance transport, stress response, development and metabolism. KEGG enrichment analysis showed that AQPs were significantly enriched in two pathways, anti-diuretic hormone-regulated reabsorption and bile secretion. These results suggested that Nile tilapia has a highly developed, albeit complex, osmotic pressure regulation system, which provided a molecular basis for exploring how these AQP members coordinate to help Nile tilapia cope with different salinities.

Genome‐wide characterization of aquaporins in Spirodela polyrhiza and expression of aquaporin gene family under high‐temperature stress

As one of the most conserved classes of gene families, aquaporins (AQP) genes play an essential role in water transport and stress resistance in organisms. However, little information was available for their evolutionary and functional roles in aquatic plant species. In the present study, gene sequences, gene structure, phylogeny, conserved motif and promoter of the AQP genes in Spirodela polyrhiza were investigated to explore the mechanisms of osmoregulation underwater. A total of 24 putative AQP genes divided into four clades representing four distinct AQPs subfamilies were identified. The gene structure and intron numbers of the AQP genes were conserved among subfamilies. The Froger's residues, conserved Ar/R selectivity filters and conserved NPA domain showed high differences among different subfamilies. Moreover, the promoter profiling of SpAQP genes for conserved cis‐acting regulatory elements revealed enrichment of cis‐elements involved in light response and stress responsiveness, reflecting their varying gene expression pattern. Our results demonstrated that the AQP genes in the S. polyrhiza were similar to those in the Zostera marina and might have experienced adaptive evolution to water. Transcriptome results showed that the SpTIP2‐3, SpPIP2‐2, SpPIP1‐3, SpTIP4‐3 and SpNIP5‐2 were expressed significantly among different treatments indicating they might play important roles under temperature stress. These data offer valuable sight into understanding the adaptation to the water of the S. polyrhiza. They may further inform our understanding of the evolution of water tolerance in S. polyrhiza.

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.

Genome-Wide Identification and Expression Analyses of the Aquaporin Gene Family in Passion Fruit (Passiflora edulis), Revealing PeTIP3-2 to Be Involved in Drought Stress.

Aquaporins (AQPs) in plants can transport water and small molecules, and they play an important role in plant development and abiotic stress response. However, to date, a comprehensive study on AQP family members is lacking. In this study, 27 AQP genes were identified from the passion fruit genome and classified into four groups (NIP, PIP, TIP, SIP) on the basis of their phylogenetic relationships. The prediction of protein interactions indicated that the AQPs of passion fruit were mainly associated with AQP family members and boron protein family genes. Promoter cis-acting elements showed that most PeAQPs contain light response elements, hormone response elements, and abiotic stress response elements. According to collinear analysis, passion fruit is more closely related to Arabidopsis than rice. Furthermore, three different fruit ripening stages and different tissues were analyzed on the basis of the transcriptome sequencing results for passion fruit AQPs under drought, high-salt, cold and high-temperature stress, and the results were confirmed by qRT-PCR. The results showed that the PeAQPs were able to respond to different abiotic stresses, and some members could be induced by and expressed in response to multiple abiotic stresses at the same time. Among the three different fruit ripening stages, 15 AQPs had the highest expression levels in the first stage. AQPs are expressed in all tissues of the passion fruit. One of the passion fruit aquaporin genes, PeTIP3-2, which was induced by drought stress, was selected and transformed into Arabidopsis. The survival rate of transgenic plants under drought stress treatment is higher than that of wild-type plants. The results indicated that PeTIP3-2 was able to improve the drought resistance of plants. Our discovery lays the foundation for the functional study of AQPs in passion fruit.

Identification of Aquaporin Gene Family in Response to Natural Cold Stress in Ligustrum × vicaryi Rehd.

Plants are susceptible to a variety of abiotic stresses during the growing period, among which low temperature is one of the more frequent stress factors. Maintaining water balance under cold stress is a difficult and critical challenge for plants. Studies have shown that aquaporins located on the cytomembrane play an important role in controlling water homeostasis under cold stress, and are involved in the tolerance mechanism of plant cells to cold stress. In addition, the aquaporin gene family is closely related to the cold resistance of plants. As a major greening tree species in urban landscaping, Ligustrum× vicaryi Rehd. is more likely to be harmed by low temperature after a harsh winter and a spring with fluctuating temperatures. Screening the target aquaporin genes of Ligustrum × vicaryi responding to cold resistance under natural cold stress will provide a scientific theoretical basis for cold resistance breeding of Ligustrum × vicaryi. In this study, the genome-wide identification of the aquaporin gene family was performed at four different overwintering periods in September, November, January and April, and finally, 58 candidate Ligustrum × vicaryi aquaporin (LvAQP) genes were identified. The phylogenetic analysis revealed four subfamilies of the LvAQP gene family: 32 PIPs, 11 TIPs, 11 NIPs and 4 SIPs. The number of genes in PIPs subfamily was more than that in other plants. Through the analysis of aquaporin genes related to cold stress in other plants and LvAQP gene expression patterns identified 20 LvAQP genes in response to cold stress, and most of them belonged to the PIPs subfamily. The significantly upregulated LvAQP gene was Cluster-9981.114831, and the significantly downregulated LvAQP genes were Cluster-9981.112839, Cluster-9981.107281, and Cluster-9981.112777. These genes might play a key role in responding to cold tolerance in the natural low-temperature growth stage of Ligustrum × vicaryi.

Genome-Wide Identification of Aquaporin Gene Family in Pitaya Reveals an HuNIP6;1 Involved in Flowering Process.

Aquaporins (AQPs) are essential membrane proteins involved in seed maturation and germination, stomata movement, photosynthesis, and regulation of plant flowering processes. Pitaya flowers are open at night and wither at daybreak, which shows an obvious circadian rhythm. In this study, a comprehensive genome-wide analysis of AQPs in Hylocereus undantus was conducted to screen key genes associated with flowering processes. A total of 33 HuAQP genes were identified from the H. undantus genome. The 33 HuAQPs were grouped into four subfamilies: 10 PIPs, 13 TIPs, 8 NIPs, and 2 SIPs, which were distributed on 9 out of 11 pitaya chromosomes (Chr) (except for Chr7 and Chr10). Results from expression profiles showed that HuNIP6;1 may be involved in pitaya’s floral opening. HuNIP6;1 was localized exclusively in the cell membrane. Overexpression of HuNIP6;1 in Arabidopsis thaliana significantly promoted early flowering through regulating negative flowering regulators of MJM30, COL9, and PRR5, suggesting that HuNIP6;1 plays key roles in regulating flowering time. The present study provides the first genome-wide analysis of the AQP gene family in pitaya and valuable information for utilization of HuAQPs.

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.

Comparative Analysis of Re-Annotated Genes Provides Insight into Evolutionary Divergence and Expressions of Aquaporin Family in Pepper.

Aquaporins (AQPs) are known to have a vital role in water transport in all living organisms including agriculturally important crops, but a comprehensive genomic study of AQPs in pepper has not been implemented. Here, we updated previous gene annotations and generated a total of 259 AQP genes from five plants, including pepper. Phylogenetic and motif analyses revealed that a large proportion of pepper AQP genes belong to the specific subgroup of tonoplast intrinsic protein (TIP) subfamily, TIP4. Chromosomal localization and estimated duplication times illustrated that genes in TIP4 formed a tandem array on the short arm of chromosome 1, resulting from pepper-specific expansion after its divergence with Solanaceae species. Transcriptome analyses under various abiotic stress conditions revealed that transport-, photosystem-, and thylakoid-related genes were generally enriched in expression clusters containing AQP genes in pepper. These results provide valuable genomic resources and insight into the evolutionary mechanism that generate genomic diversity of the AQP gene family in pepper.