AcPIP2, a plasma membrane intrinsic protein from halophyte Atriplex canescens, enhances plant growth rate and abiotic stress tolerance when overexpressed in Arabidopsis thaliana

Modulation of physio-biochemical and photosynthesis parameters by overexpressing SbPIP2 gene improved abiotic stress tolerance of transgenic tobacco

The present study aims to explore the potential of a plasma-membrane localized PIP2-type aquaporin protein sourced from the halophyte Salicornia brachiata to alleviate salinity and water deficit stress tolerance in a model plant through transgenic intervention. Transgenic plants overexpressing SbPIP2 gene showed improved physio-biochemical parameters like increased osmolytes (proline, total sugar, and amino acids), antioxidants (polyphenols), pigments and membrane stability under salinity and drought stresses compared to control plants [wild type (WT) and vector control (VC) plants]. Multivariate statistical analysis showed that, under water and salinity stresses, osmolytes, antioxidants and pigments were correlated with SbPIP2-overexpressing (SbPIP2-OE) plants treated with salinity and water deficit stress, suggesting their involvement in stress tolerance. As aquaporins are also involved in CO2 transport, SbPIP2-OE plants showed enhanced photosynthesis performance than wild type upon salinity and drought stresses. Photosynthetic gas exchange (net CO2 assimilation rate, PSII efficiency, ETR, and non-photochemical quenching) were significantly higher in SbPIP2-OE plants compared to control plants (wild type and vector control plants) under both unstressed and stressed conditions. The higher quantum yield for reduction of end electron acceptors at the PSI acceptor side [Φ( R0 )] in SbPIP2-OE plants compared to control plants under abiotic stresses indicates a continued PSI functioning, leading to retained electron transport rate, higher carbon assimilation, and less ROS-mediated injuries. In conclusion, the SbPIP2 gene functionally validated in the present study could be a potential candidate for engineering abiotic stress resilience in important crops.

TaMPK2B, a member of the MAPK family in T. aestivum, enhances plant low-Pi stress tolerance through modulating physiological processes associated with phosphorus starvation defensiveness

The mitogen-activated protein kinase (MAPK) cascades are present in plant species and modulate plant growth and stress responses. This study characterizes TaMPK2B, a MAPK family gene in T. aestivum that regulates plant adaptation to low-Pi stress. TaMPK2B harbors the conserved domains involving protein phosphorylation and protein-protein interaction. A yeast two-hybrid assay reveals an interaction between TaMPK2B and TaMPKK2 and between the latter and TaMPKKK;A, suggesting that all comprise a MAPK signaling cascade TaMPKKK;A-TaMPKK2-TaMPK2B. TaMPK2B expression levels were elevated in roots and leaves under a Pi starvation (PS) condition. Additionally, the induced TaMPK2B transcripts under PS in tissues were gradually restored following the Pi normal recovery condition. TaMPK2B overexpression conferred on plants improved PS adaptation; the tobacco lines with TaMPK2B overexpression enhanced the plant's dry mass production, Pi uptake capacity, root system architecture (RSA) establishment, and ROS homeostasis relative to wild type under PS treatment. Moreover, the transcripts of genes in phosphate transporter (PT), PIN-FORMED, and antioxidant enzyme (AE) families, including NtPT3 and NtPT4, NtPIN9, and NtMnSOD1 and NtPOD1;7, were elevated in Pi-deprived lines overexpressing TaMPK2B. Transgene analyses validated their functions in regulating Pi uptake, RSA establishment, and AE activities of plants treated by PS. These results suggest that TaMPK2B-mediated plant PS adaptation is correlated with the modified transcription of distinct PT, PIN, and AE genes. Our investigation suggests that TaMPK2B is one of the crucial regulators in plant low-Pi adaptation by improving Pi uptake, RSA formation, and ROS homeostasis via transcriptionally regulating genes associated with the above physiological processes.

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.

Atriplex canescens, a valuable plant in soil rehabilitation and forage production. A review

A. canescens (Pure) Nutt. is a halophytic forage shrub distributes in arid and semiarid regions, which has great use potential in disturbed lands for its strong adaptability and feeding value. At present, land degradation caused by salinization, desertification and heavy metal pollution is still expanding all over the world, meanwhile, stock raising in arid and semi-arid areas may face more shortage of forage supply. Although A. canescens is much accounted of in some regions, its application values are not widely concerned in some countries such as China. Therefore, a comprehensive understanding is needed to promote its application in these regions. In the review, we introduced the morphological and physiological characteristics of A. canescens, summarized its ecological and economic values, and we also discussed its use prospect and main problems in China. This review could be helpful for understanding of A. canescens adaptive characteristics and application values, thus promote its reasonable popularization and use in areas in need.

Transcript profiles analysis of citrus aquaporins in response to fruit water loss during storage

Water loss is an essential factor that affects the maintenance of quality of citrus fruit during postharvest handling and storage. Aquaporins (AQPs) play an important role in the transport of water across membranes. However, the expression profiling of AQPs is incomplete for citrus fruits during storage. In this study, a post-harvest storage experiment was performed using sweet orange fruits to determine changes in water loss and fruit quality. Also, genome-wide expression analysis of CsAQP genes was carried out in fruit of different citrus varieties during storage. Low humidity storage conditions accelerated the postharvest water loss and texture decline and increased the TSS content in the fruit. A total of 39 non-redundant CsAQP genes were identified. A comprehensive analysis of these genes demonstrated that all AQPs had conserved filter motifs in the different citrus varieties examined. Moreover, multiple expression analysis revealed AQPs had complex expression profiles upon water loss in citrus fruit, being time-specific in tight-skin varieties (orange and pomelo varieties), tissue-specific between peel and pulp, and variety-specific between loose-skin (mandarin varieties) and tight-skin varieties (such as sweet orange and pummelo). These results indicated that the relative humidity in storage environment affected the postharvest water loss and quality of citrus fruit. Besides, the alternation in AQPs expression may partially account for the different water loss ratio in citrus varieties and the transfer of water between the peel and the pulp of citrus fruit during storage.

ERAD-related E2 and E3 enzymes modulate the drought response by regulating the stability of PIP2 aquaporins

Endoplasmic reticulum-associated degradation (ERAD) is known to regulate plant responses to diverse stresses, yet its underlying molecular mechanisms and links to various stress signaling pathways are poorly understood. Here, we show that the ERAD component ubiquitin-conjugating enzyme UBC32 positively regulates drought tolerance in Arabidopsis thaliana by targeting the aquaporins PIP2;1 and PIP2;2 for degradation. Furthermore, we demonstrate that the RING-type ligase Rma1 acts together with UBC32 and that the E2 activity of UBC32 is essential for the ubiquitination of Rma1. This complex ubiquitinates a phosphorylated form of PIP2;1 at Lys276 to promote its degradation, thereby enhancing plant drought tolerance. Extending these molecular insights into crops, we show that overexpression of Arabidopsis UBC32 also improves drought tolerance in rice (Oryza sativa). Thus, beyond uncovering the molecular basis of an ERAD-regulated stress response, our study suggests multiple potential strategies for engineering crops with improved drought tolerance.

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

BACKGROUND

Canavalia 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.

RESULTS

We 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.

CONCLUSIONS

Our 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.

Poplar aquaporin PIP1;1 promotes Arabidopsis growth and development

BACKGROUND

Root 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.

RESULTS

In 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.

CONCLUSIONS

Taken 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.

Insight of transcriptional regulators reveals the tolerance mechanism of carpet-grass (Axonopus compressus) against drought

BACKGROUND

Carpet grass [Axonopus compressus (L.)] is an important warm-season perennial grass around the world and is known for its adaptability to varied environmental conditions. However, Carpet grass lacks enough data in public data banks, which confined our comprehension of the mechanisms of environmental adaptations, gene discovery, and development of molecular markers. In current study, the DEGs (differentially expressed genes) in Axonopus compressus under drought stress (DS) were identified and compared with CK (control) by RNA-Seq.

RESULTS

A total of 263,835 unigenes were identified in Axonopus compressus, and 201,303 (also added to the numbers of the remaining 2 databases) a sequence of unigenes significantly matched in at least one of the seven databases. A total of 153,697 (58.25%) unigenes classified to 144 KEGG pathways, and 7444 unigenes were expressed differentially between DS and CK, of which 4249 were up-regulated and 3195 were down-regulated unigenes. Of the 50 significantly enriched GO terms, 18, 6, and 14 items were related to BP, CC, and MF respectively. Analysis of KEGG enrichment revealed 2569 DEGs involved in 143 different pathways, under drought stress. 2747 DEGs were up-regulated and 2502 DEGs were down-regulated. Moreover, we identified 352 transcription factors (TFs) in Axonopus compressus, of which 270 were differentially expressed between CK and DS. The qRT-PCR validation experiment also supports the transcriptional response of Axonopus compressus against drought. Accuracy of transcriptome unigenes of Axonopus compressus was assessed with BLAST, which showed 3300 sequences of Axonopus compressus in the NCBI.

CONCLUSION

The 7444 unigenes were found to be between DS and CK treatments, which indicate the existence of a strong mechanism of drought tolerance in Axonopus compressus. The current findings provide the first framework for further investigations for the particular roles of these unigenes in Axonopus compressus in response to drought.

Ectopic Expression of CrPIP2;3, a Plasma Membrane Intrinsic Protein Gene from the Halophyte Canavalia rosea, Enhances Drought and Salt-Alkali Stress Tolerance in Arabidopsis

Aquaporins are channel proteins that facilitate the transmembrane transport of water and other small neutral molecules, thereby playing vital roles in maintaining water and nutrition homeostasis in the life activities of all organisms. Canavalia rosea, a seashore and mangrove-accompanied halophyte with strong adaptability to adversity in tropical and subtropical regions, is a good model for studying the molecular mechanisms underlying extreme saline-alkaline and drought stress tolerance in leguminous plants. In this study, a PIP2 gene (CrPIP2;3) was cloned from C. rosea, and its expression patterns and physiological roles in yeast and Arabidopsis thaliana heterologous expression systems under high salt-alkali and high osmotic stress conditions were examined. The expression of CrPIP2;3 at the transcriptional level in C. rosea was affected by high salinity and alkali, high osmotic stress, and abscisic acid treatment. In yeast, the expression of CrPIP2;3 enhanced salt/osmotic and oxidative sensitivity under high salt/osmotic and H₂O₂ stress. The overexpression of CrPIP2;3 in A. thaliana could enhance the survival and recovery of transgenic plants under drought stress, and the seed germination and seedling growth of the CrPIP2;3 OX (over-expression) lines showed slightly stronger tolerance to high salt/alkali than the wild-type. The transgenic plants also showed a higher response level to high-salinity and dehydration than the wild-type, mostly based on the up-regulated expression of salt/dehydration marker genes in A. thaliana plants. The reactive oxygen species (ROS) staining results indicated that the transgenic lines did not possess stronger ROS scavenging ability and stress tolerance than the wild-type under multiple stresses. The results confirmed that CrPIP2;3 is involved in the response of C. rosea to salt and drought, and primarily acts by mediating water homeostasis rather than by acting as an ROS transporter, thereby influencing physiological processes under various abiotic stresses in plants.

Are Aquaporins Expressed in Stomatal Complexes Promising Targets to Enhance Stomatal Dynamics?

The opening and closure of stomata depend on the turgor pressure adjustment by the influx or efflux of ions and water in guard cells. In this process, aquaporins may play important roles by facilitating the transport of water and other small molecules. In this perspective, we consider the potential roles of aquaporins in the membrane diffusion of different molecules (H₂O, CO₂, and H₂O₂), processes dependent on abscisic acid and CO₂ signaling in guard cells. While the limited data already available emphasizes the roles of aquaporins in stomatal movement, we propose additional approaches to elucidate the specific roles of single or several aquaporin isoforms in the stomata and evaluate the perspectives aquaporins might offer to improve stomatal dynamics.

Physiological and transcriptome analyses of the effects of exogenous dopamine on drought tolerance in apple

Water shortage is one of the main limiting factors in apple (Malus domestica Borkh.) production. Although dopamine is produced in plants and has been linked with response to abiotic stress, the underlying mechanism remains unknown. In this study, physiological analyses revealed that pretreatment with 100 μM dopamine alleviated drought stress in apple seedlings. Dopamine inhibited the degradation of photosynthetic pigments and increased net photosynthetic rate under drought stress. Dopamine also reduced H₂O₂ content, possibly through direct scavenging and by mediating the antioxidant enzyme activity. Seedlings pretreated with dopamine had higher sucrose and malic acid contents but lower starch accumulation in their leaves. RNA-Seq analysis identified 1052 differentially expressed genes (DEGs) between non-treated and dopamine-pretreated plants under drought. An in-depth analysis of these DEGs revealed that dopamine regulated the expression of genes related to metabolism of nitrogen, secondary compounds, and amino acids under drought stress. In addition, dopamine may improve apple drought tolerance by activating Ca²⁺ signaling pathways through increased expression of CNGC and CAM/CML family genes. Moreover, analysis of transcription factor expression suggested that dopamine affected drought tolerance mainly through the regulation of WRKY, ERF, and NAC transcription factors.

Identification of candidate genes related to salt tolerance of the secretohalophyte Atriplex canescens by transcriptomic analysis

BACKGROUND

Atriplex canescens is a typical C₄ secretohalophyte with salt bladders on the leaves. Accumulating excessive Na⁺ in tissues and salt bladders, maintaining intracellular K⁺ homeostasis and increasing leaf organic solutes are crucial for A. canescens survival in harsh saline environments, and enhanced photosynthetic activity and water balance promote its adaptation to salt. However, the molecular basis for these physiological mechanisms is poorly understood. Four-week-old A. canescens seedlings were treated with 100 mM NaCl for 6 and 24 h, and differentially expressed genes in leaves and roots were identified, respectively, with Illumina sequencing.

RESULTS

In A. canescens treated with 100 mM NaCl, the transcripts of genes encoding transporters/channels for important nutrient elements, which affect growth under salinity, significantly increased, and genes involved in exclusion, uptake and vacuolar compartmentalization of Na⁺ in leaves might play vital roles in Na⁺ accumulation in salt bladders. Moreover, NaCl treatment upregulated the transcripts of key genes related to leaf organic osmolytes synthesis, which are conducive to osmotic adjustment. Correspondingly, aquaporin-encoding genes in leaves showed increased transcripts under NaCl treatment, which might facilitate water balance maintenance of A. canescens seedlings in a low water potential condition. Additionally, the transcripts of many genes involved in photosynthetic electron transport and the C₄ pathway was rapidly induced, while other genes related to chlorophyll biosynthesis, electron transport and C₃ carbon fixation were later upregulated by 100 mM NaCl.

CONCLUSIONS

We identified many important candidate genes involved in the primary physiological mechanisms of A. canescens salt tolerance. This study provides excellent gene resources for genetic improvement of salt tolerance of important crops and forages.

AcERF2, an ethylene-responsive factor of Atriplex canescens, positively modulates osmotic and disease resistance in Arabidopsis thaliana

Ethylene-responsive factors (ERFs) comprise a large family of transcription factors in plants and play important roles in developmental processes and stress responses. Here, we characterized a novel AP2/ERF transcription factor, AcERF2, from the halophyte Atriplex canescens (four-wing saltbush, Chenopodiaceae). AcERF2 was proved to be a transcriptional activator in yeast and localized to the nucleus upon transient expression in Nicotiana benthamiana, indicating its potential role as a transcription factor. Overexpression of AcERF2 driven by a CaMV35S promoter led to decreased accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), and increased antioxidant enzymatic activities, as well as rapid stomatal closure under osmotic treatment in Arabidopsis. Arabidopsis plants overexpressing AcERF2 were hypersensitive to abscisic acid (ABA) during germination, seedling establishment, and primary root elongation, and exhibited significant tolerance to osmotic stress. Furthermore, overexpression of AcERF2 induced transcript accumulation of plant defense-related genes (PR1, PR2, PR5, ERF1 and ERF3) and increased Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and the necrotrophic fungal pathogen Botrytis cinerea. These results suggest that AcERF2 may play a positive modulation role in response to osmotic stress and pathogen infection in plants.

Exploration for the Salinity Tolerance-Related Genes from Xero-Halophyte Atriplex canescens Exploiting Yeast Functional Screening System

Plant productivity is limited by salinity stress, both in natural and agricultural systems. Identification of salt stress-related genes from halophyte can provide insights into mechanisms of salt stress tolerance in plants. Atriplex canescens is a xero-halophyte that exhibits optimum growth in the presence of 400 mM NaCl. A cDNA library derived from highly salt-treated A. canescens plants was constructed based on a yeast expression system. A total of 53 transgenic yeast clones expressing enhanced salt tolerance were selected from 10⁵ transformants. Their plasmids were sequenced and the gene characteristics were annotated using a BLASTX search. Retransformation of yeast cells with the selected plasmids conferred salt tolerance to the resulting transformants. The expression patterns of 28 of these stress-related genes were further investigated in A. canescens leaves by quantitative reverse transcription-PCR. In this study, we provided a rapid and robust assay system for large-scale screening of genes for varied abiotic stress tolerance with high efficiency in A. canescens.

Carbon dioxide and water transport through plant aquaporins

Aquaporins are channel proteins that function to increase the permeability of biological membranes. In plants, aquaporins are encoded by multigene families that have undergone substantial diversification in land plants. The plasma membrane intrinsic proteins (PIPs) subfamily of aquaporins is of particular interest given their potential to improve plant water relations and photosynthesis. Flowering plants have between 7 and 28 PIP genes. Their expression varies with tissue and cell type, through development and in response to a variety of factors, contributing to the dynamic and tissue specific control of permeability. There are a growing number of PIPs shown to act as water channels, but those altering membrane permeability to CO₂ are more limited. The structural basis for selective substrate specificities has not yet been resolved, although a few key amino acid positions have been identified. Several regions important for dimerization, gating and trafficking are also known. PIP aquaporins assemble as tetramers and their properties depend on the monomeric composition. PIPs control water flux into and out of veins and stomatal guard cells and also increase membrane permeability to CO₂ in mesophyll and stomatal guard cells. The latter increases the effectiveness of Rubisco and can potentially influence transpiration efficiency.

The bamboo aquaporin gene PeTIP4;1-1 confers drought and salinity tolerance in transgenic Arabidopsis

PeTIP4;1-1, an aquaporin gene involved in bamboo shoot growth, is regulated by abiotic stresses. Overexpression of PeTIP4;1-1 confers drought and salinity tolerance in transgenic Arabidopsis. Aquaporins play a central role in numerous physiological processes throughout plant growth and development. PeTIP4;1-1, an aquaporin gene isolated from moso bamboo (Phyllostachys edulis), comprises an open reading frame (ORF) of 756 bp encoding a peptide of 251 amino acids. The genomic sequence corresponding to the ORF of PeTIP4;1-1 was 1777 bp and contained three exons separated by two introns. PeTIP4;1-1 was constitutively expressed at the highest level in culms, and the expression level was elevated with increasing height of the bamboo shoot. PeTIP4;1-1 was significantly up-regulated in response to drought and salinity stresses in bamboo roots and leaves. To investigate the role of PeTIP4;1-1 in response to drought and salinity stresses, transgenic Arabidopsis plants overexpressing PeTIP4;1-1 under the control of CaMV 35S promoter were generated and subjected to morphological and physiological assays. Compared with Col-0, the transgenic plants showed enhanced tolerance to drought and salinity stresses and produced longer taproots, which had more green leaves, higher F _v/F _m and NPQ values, higher activities of SOD, POD and CAT, lower MDA concentration and higher water content. Transcript levels of three stress-related genes (AtP5CS, AtNHX1 and AtLEA) were enhanced. These results indicated that PeTIP4;1-1 might play an important function in response to drought and salinity stresses, and is a candidate gene for breeding of stress tolerance in other crops through genetic engineering.

Tartary buckwheat FtMYB10 encodes an R2R3-MYB transcription factor that acts as a novel negative regulator of salt and drought response in transgenic Arabidopsis

Tartary buckwheat is a strongly abiotic, resistant coarse cereal, but its tolerance mechanisms for stress are largely unknown. MYB transcription factors play key roles in various physiological, biochemical and molecular responses, which can both positively and negatively regulate the stress tolerance of plants. In this study, we report that the expression of FtMYB10, a R2R3-MYB gene from Tartary buckwheat, was induced significantly by ABA and drought treatments. A seed germination test under ABA treatment indicated that transgenic lines were less sensitive to ABA. The overexpression of FtMYB10 in Arabidopsis reduced drought and salt tolerance. Further studies showed that the proline contents in the transgenic plants are markedly decreased associated with reduced expression of the P5CS1 gene under both normal and stress conditions. Furthermore, the expression of some stress-responsive genes, including DREB1/CBFs, RD29B, RD22, and several genes of the DRE/CRT class, decreased in response to FtMYB10 overexpression in Arabidopsis. These results suggest that FtMYB10 may play a key role in ABA signaling feedback regulation and act as a novel negative regulator of salt and drought stress tolerance in plants.

AcEBP1, an ErbB3-Binding Protein (EBP1) from halophyte Atriplex canescens, negatively regulates cell growth and stress responses in Arabidopsis

An ErbB-3-binding protein gene AcEBP1, also known as proliferation-associated 2G4 gene (PA2G4s) belonging to the M24 superfamily, was obtained from the saltbush Atriplex canescens. Subcellular localization imaging showed the fusion protein AcEBP1-eGFP was located in the nucleus of epidermal cells in Nicotiana benthamiana. The AcEBP1 gene expression levels were up-regulated under salt, osmotic stress, and hormones treatment as revealed by qRT-PCR. Overexpression of AcEBP1 in Arabidopsis demonstrated that AcEBP1 was involved in root cell growth and stress responses (NaCl, osmotic stress, ABA, low temperature, and drought). These phenotypic data were correlated with the expression patterns of stress responsive genes and PR genes. The AcEBP1 transgenic Arabidopsis plants also displayed increased sensitivity under low temperature and evaluated resistance to drought stress. Together, these results demonstrate that AcEBP1 negatively affects cell growth and is a regulator under stress conditions.

Identification of Drought Tolerant Mechanisms in Maize Seedlings Based on Transcriptome Analysis of Recombination Inbred Lines

Zea mays is an important crop that is sensitive to drought stress, but survival rates and growth status remain strong in some drought-tolerant lines under stress conditions. Under drought conditions, many biological processes, such as photosynthesis, carbohydrate metabolism and energy metabolism, are suppressed, while little is known about how the transcripts of genes respond to drought stress in the genome-wide rang in the seedling stage. In our study, the transcriptome profiles of two maize recombination inbred lines (drought-tolerant RIL70 and drought-sensitive RIL93) were analyzed at different drought stages to elucidate the dynamic mechanisms underlying drought tolerance in maize seedlings during drought conditions. Different numbers of differentially expressed genes presented in the different stages of drought stress in the two RILs, for the numbers of RIL93 vs. RIL70 were: 9 vs. 358, 477 vs. 103, and 5207 vs. 152 respectively in DT1, DT2, and DT5. Gene Ontology enrichment analysis revealed that in the initial drought-stressed stage, the primary differentially expressed genes involved in cell wall biosynthesis and transmembrane transport biological processes were overrepresented in RIL70 compared to RIL93. On the contrary, differentially expressed genes profiles presented at 2 and 5 day-treatments, the primary differentially expressed genes involved in response to stress, protein folding, oxidation-reduction, photosynthesis and carbohydrate metabolism, were overrepresented in RIL93 compared to RIL70. In addition, the transcription of genes encoding key members of the cell cycle and cell division processes were blocked, but ABA- and programmed cell death-related processes responded positively in RIL93. In contrast, the expression of cell cycle genes, ABA- and programmed cell death-related genes was relatively stable in RIL70. The results we obtained supported the working hypothesis that signaling events associated with turgor homeostasis, as established by cell wall biosynthesis regulation- and aquaporin-related genes, responded early in RIL70, which led to more efficient detoxification signaling (response to stress, protein folding, oxidation-reduction) during drought stress. This energy saving response at the early stages of drought should facilitate more cell activity under stress conditions and result in drought tolerance in RIL70.

Wheat mitogen-activated protein kinase gene TaMPK4 improves plant tolerance to multiple stresses through modifying root growth, ROS metabolism, and nutrient acquisitions

KEY MESSAGE

Wheat MAPK member TaMPK4 responds to abiotic stresses of Pi and N deprivations and high salinity and is crucial in regulating plant tolerance to aforementioned stresses. Mitogen-activated protein kinase (MAPK) cascades are important signal transduction modules in regulating plant responses to various environmental stresses. In this study, a wheat MAPK member referred to TaMPK4 was characterized for its roles in mediating plant tolerance to diverse stresses. TaMPK4 shares conserved domains generally identified in plant MAPKs and possesses in vitro kinase activity. Under stresses of Pi and N deprivations and high salinity, TaMPK4 was strongly upregulated and its expressions were restored upon recovery treatments from above stresses. Sense- and antisense-expressing TaMPK4 in tobacco significantly modified plant growth under the stress conditions and dramatically modified the root architecture through transcriptional regulation of the auxin transport-associated genes NtPIN3 and NtPIN9, whose downregulated expressions dramatically reduced the root growth. Compared with wild type (WT), the antioxidant enzymatic activities under the stress conditions, P accumulation under P deprivation, and N amount under N deficiency were altered dramatically in the transgenic plants, showing higher in the TaMPK4-overexpressing and lower in the TaMPK4-knockout plants, which were in concordance with the modified expressions of a set of antioxidant enzyme genes (NtPOD2;1, NtPOD9, NtSOD2, NtFeSOD, and NtCAT), two phosphate transporter genes (NtPT and NtPT2), and two nitrate transporter genes (NtNRT1.1-s and NtNRT1.1-t), respectively. Downregulated expression of above genes in tobacco largely reduced the plant growth, and Pi and N acquisitions under the stress conditions. TaMPK4 also involved regulations of plant K(+) and osmolyte contents under high salinity. Thus, TaMPK4 is functional in regulating plant tolerance to diverse stresses through modifying various biological processes.