Over-expression of GsZFP1, an ABA-responsive C2H2-type zinc finger protein lacking a QALGGH motif, reduces ABA sensitivity and decreases stomata size

Heterologous expression of Zygophyllum xanthoxylon zinc finger protein gene (ZxZF) enhances the tolerance of poplar photosynthetic function to drought stress

The ZxZF transcription factor (TF) of Zygophyllum xanthoxylon (Bunge) Maxim, an extremely drought-resistant woody plant, is a C₂H₂ zinc finger protein. Studies have shown that C₂H₂ zinc finger proteins play important roles in activating stress-related genes and enhancing plant resistance. However, their function in regulating plant photosynthesis under drought stress is not well understood. Since poplar is an important greening and afforestation tree species, it is particularly important to cultivate excellent drought-tolerant varieties. The ZxZF transcription factor (TF) was heterogeneously expressed in Euroamerican poplar (Populus × euroameracana cl.'Bofengl') by genetic transformation. Based on the mechanism and potential function of poplar photosynthesis regulated by ZxZF under drought stress, transcriptomic and physiological determinations were used to reveal the important role of this gene in improving the drought resistance of poplar. The results showed that the overexpression of ZxZF TF in transgenic poplars could improve the inhibition of Calvin cycle by regulating stomatal opening and increasing the concentration of intercellular CO₂. The chlorophyll content, photosynthetic performance index, and photochemical efficiency of transgenic lines under drought stress were significantly higher than those of the wild type (WT). The overexpression of ZxZF TFs could alleviate the degree of photoinhibition of photosystems II and I under drought stress and maintain the efficiency of light energy capture and the photosynthetic electron transport chain. The transcriptomic data also showed that differentially expressed genes between the transgenic poplar and WT under drought stress were primarily enriched in metabolic pathways related to photosynthesis, such as photosynthesis, photosynthesis-antenna protein, porphyrin and chlorophyll metabolism, and photosynthetic carbon fixation, and the downregulation of genes related to chlorophyll synthesis, photosynthetic electron transport and Calvin cycle were alleviated. In addition, the overexpression of ZxZF TF can alleviate the inhibition of NADH dehydrogenase-like (NDH) cyclic electron flow of the poplar NDH pathway under drought stress, which plays an important role in reducing the excess pressure of electrons on the photosynthetic electron transport chain and maintaining the normal photosynthetic electron transport. In summary, the overexpression of ZxZF TFs can effectively alleviate the inhibition of drought on the assimilation of carbon in poplar and have a positive impact on light energy capture, the orderly transport of photosynthetic electron transport chain and the integrity of the photosystem, which is highly significant to acheivean in-depth understanding of the function of ZxZF TFs. This also provides an important basis for the breeding of new transgenic poplar varieties.

The C2 H2 -type zinc finger transcription factor OSIC1 positively regulates stomatal closure under osmotic stress in poplar

Salt and drought impair plant osmotic homeostasis and greatly limit plant growth and development. Plants decrease stomatal aperture to reduce water loss and maintain osmotic homeostasis, leading to improved stress tolerance. Herein, we identified the C₂ H₂ transcription factor gene OSMOTIC STRESS INDUCED C₂ H₂ 1 (OSIC1) from Populus alba var. pyramidalis to be induced by salt, drought, polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA). Overexpression of OSIC1 conferred transgenic poplar more tolerance to high salinity, drought and PEG6000 treatment by reducing stomatal aperture, while its mutant generated by the CRISPR/Cas9 system showed the opposite phenotype. Furthermore, OSIC1 directly up-regulates PalCuAOζ in vitro and in vivo, encoding a copper-containing polyamine oxidase, to enhance H₂ O₂ accumulation in guard cells and thus modulates stomatal closure when stresses occur. Additionally, ABA-, drought- and salt-induced PalMPK3 phosphorylates OSIC1 to increase its transcriptional activity to PalCuAOζ. This regulation of OSIC1 at the transcriptional and protein levels guarantees rapid stomatal closure when poplar responds to osmotic stress. Our results revealed a novel transcriptional regulatory mechanism of H₂ O₂ production in guard cells mediated by the OSIC1-PalCuAOζ module. These findings deepen our understanding of how perennial woody plants, like poplar, respond to osmotic stress caused by salt and drought and provide potential targets for breeding.

Pinpointing genomic loci for drought-induced proline and hydrogen peroxide accumulation in bread wheat under field conditions

BACKGROUND

Proline (Pro) and hydrogen peroxide (H₂O₂) play a critical role in plants during drought adaptation. Genetic mapping for drought-induced Pro and H₂O₂ production under field conditions is very limited in crop plants since their phenotyping with large populations is labor-intensive. A genome-wide association study (GWAS) of a diversity panel comprised of 184 bread wheat cultivars grown in natural field (control) and rain-out shelter (drought) environments was performed to identify candidate loci and genes regulating Pro and H₂O₂ accumulation induced by drought.

RESULTS

The GWAS identified top significant marker-trait associations (MTAs) on 1A and 2A chromosomes, respectively for Pro and H₂O₂ in response to drought. Similarly, MTAs for stress tolerance index (STI) of Pro and H₂O₂ were identified on 5B and 1B chromosomes, respectively. Total 143 significant MTAs were identified including 36 and 71 were linked to drought and 2 and 34 were linked to STI for Pro and H₂O_2, respectively. Next, linkage disequilibrium analysis revealed minor alleles of significant single-markers and haplotypes were associated with higher Pro and H₂O₂ accumulation under drought. Several putative candidate genes for Pro and H₂O₂ content encode proteins with kinase, transporter or protein-binding activities.

CONCLUSIONS

The identified genetic factors associated with Pro and H₂O₂ biosynthesis underlying drought adaptation lay a fundamental basis for functional studies and future marker-assisted breeding programs.

Genome-wide analysis of the C2H2 zinc finger protein gene family and its response to salt stress in ginseng, Panax ginseng Meyer

The C2H2 zinc finger protein (C2H2-ZFP) gene family plays important roles in response to environmental stresses and several other biological processes in plants. Ginseng is a precious medicinal herb cultivated in Asia and North America. However, little is known about the C2H2-ZFP gene family and its functions in ginseng. Here, we identified 115 C2H2-ZFP genes from ginseng, defined as the PgZFP gene family. It was clustered into five groups and featured with eight conserved motifs, with each gene containing one to six of them. The family genes are categorized into 17 gene ontology subcategories and have numerous regulatory elements responsive to a variety of biological process, suggesting their functional differentiation. The 115 PgZFP genes were spliced into 228 transcripts at seed setting stage and varied dramatically in expression across tissues, developmental stages, and genotypes, but they form a co-expression network, suggesting their functional correlation. Furthermore, four genes, PgZFP31, PgZFP78-01, PgZFP38, and PgZFP39-01, were identified from the gene family that were actively involved in plant response to salt stress. These results provide new knowledge on origin, differentiation, evolution, and function of the PgZFP gene family and new gene resources for C2H2-ZFP gene research and application in ginseng and other plant species.

A C2H2-Type Zinc-Finger Protein from Millettia pinnata, MpZFP1, Enhances Salt Tolerance in Transgenic Arabidopsis

C2H2 zinc finger proteins (ZFPs) play important roles in plant development and response to abiotic stresses, and have been studied extensively. However, there are few studies on ZFPs in mangroves and mangrove associates, which represent a unique plant community with robust stress tolerance. MpZFP1, which is highly induced by salt stress in the mangrove associate Millettia pinnata, was cloned and functionally characterized in this study. MpZFP1 protein contains two zinc finger domains with conserved QALGGH motifs and targets to the nucleus. The heterologous expression of MpZFP1 in Arabidopsis increased the seeds' germination rate, seedling survival rate, and biomass accumulation under salt stress. The transgenic plants also increased the expression of stress-responsive genes, including RD22 and RD29A, and reduced the accumulation of reactive oxygen species (ROS). These results indicate that MpZFP1 is a positive regulator of plant responses to salt stress due to its activation of gene expression and efficient scavenging of ROS.

Transcriptome analysis of salt stress responsiveness in the seedlings of wild and cultivated Ricinus communis L

Soil salinity is one of the major environmental factors, influencing agricultural productivity of crops. As a non-edible and ideal oilseed crop, castor (Ricinus communis L.) has great industrial value in biofuel, but molecular mechanisms of salt stress regulation are still unknown. In this study, the differentially expressed genes (DEGs) for differential salt tolerance in two castor cultivar (wild castor : Y, cultivated castor 'Tongbi 5': Z) were identified. 12 libraries were sampled for Illumina high-throughput sequencing to consider 132,426 nonredundant unigenes and 31,221 gene loci. Multiple phytohormones and transcription factors (TFs) were correlated with salt-tolerance and differently enriched in these two genotypes. The type 2C protein phosphatases (PP2C) homologs were all upregulated under salt stress. Importantly, IAA (1), DELLA (1) and Jasmonate zim domain (JAZ) (1) were also identified and found to be differentially expressed. Based on the co-expressed module by regulatory networks and heatmap analysis, ERF/AP2, WRKY and bHLH families were prominently participate in high salt stress response of wild and cultivated castor. Finally, these results highlight that the hub DEGs and families were more accumulated in cultivated castor than those in wild castor, providing novel insights into the salinity adaptive mechanisms and genetic improvement in castor.

A Leymus chinensis histidine-rich Ca2+-binding protein binds Ca2+/Zn2+ and suppresses abscisic acid signaling in Arabidopsis

Intracellular Ca²⁺ plays an essential role in plant cellular sensing of various environmental stress signals by modulating the activity of Ca²⁺-binding proteins. Leymus chinensis is a dominant forage grass widely distributed in the Eurasian Steppe that is well adapted to drought and salty soils common in the region. Through transcript profiling of L. chinensis roots, we identified a transcript predicted to encode histidine-rich calcium-binding protein (HRC), a protein recently characterized in wheat. L. chinensis HRC (LcH RC) localized in the nucleus, as demonstrated using a transient gene expression method that we developed for this species. Different regions of LcHRC showed affinity for either Ca²⁺ or Zn²⁺, but not Mg²⁺ and Mn²⁺. Arabidopsis thaliana seedlings heterologously overexpressing LcHRC showed greater sensitivity to abscisic acid (ABA), along with decreased expression of some ABA-induced marker genes, but no increase in ABA content. Screening a Arabidopsis cDNA yeast library identified a Tudor/PWWP/MBT-domain-containing protein (AtPWWP3) that interacts with LcHRC. AtPWWP3 also localized in the nucleus and is predicted to mediate gene expression by modifying histone deacetylation. Based on these results, we propose a functional model of LcHRC action.

Heterologous Expression of a Glycine soja C2H2 Zinc Finger Gene Improves Aluminum Tolerance in Arabidopsis

Aluminum (Al) toxicity limits plant growth and has a major impact on the agricultural productivity in acidic soils. The zinc-finger protein (ZFP) family plays multiple roles in plant development and abiotic stresses. Although previous reports have confirmed the function of these genes, their transcriptional mechanisms in wild soybean (Glycine soja) are unclear. In this study, GsGIS3 was isolated from Al-tolerant wild soybean gene expression profiles to be functionally characterized in Arabidopsis. Laser confocal microscopic observations demonstrated that GsGIS3 is a nuclear protein, containing one C2H2 zinc-finger structure. Our results show that the expression of GsGIS3 was of a much higher level in the stem than in the leaf and root and was upregulated under AlCl3, NaCl or GA3 treatment. Compared to the control, overexpression of GsGIS3 in Arabidopsis improved Al tolerance in transgenic lines with more root growth, higher proline and lower Malondialdehyde (MDA) accumulation under concentrations of AlCl3. Analysis of hematoxylin staining indicated that GsGIS3 enhanced the resistance of transgenic plants to Al toxicity by reducing Al accumulation in Arabidopsis roots. Moreover, GsGIS3 expression in Arabidopsis enhanced the expression of Al-tolerance-related genes. Taken together, our findings indicate that GsGIS3, as a C2H2 ZFP, may enhance tolerance to Al toxicity through positive regulation of Al-tolerance-related genes.

C2H2 Zinc Finger Proteins: Master Regulators of Abiotic Stress Responses in Plants

Abiotic stresses such as drought and salinity are major environmental factors that limit crop yields. Unraveling the molecular mechanisms underlying abiotic stress resistance is crucial for improving crop performance and increasing productivity under adverse environmental conditions. Zinc finger proteins, comprising one of the largest transcription factor families, are known for their finger-like structure and their ability to bind Zn2+. Zinc finger proteins are categorized into nine subfamilies based on their conserved Cys and His motifs, including the Cys2/His2-type (C2H2), C3H, C3HC4, C2HC5, C4HC3, C2HC, C4, C6, and C8 subfamilies. Over the past two decades, much progress has been made in understanding the roles of C2H2 zinc finger proteins in plant growth, development, and stress signal transduction. In this review, we focus on recent progress in elucidating the structures, functions, and classifications of plant C2H2 zinc finger proteins and their roles in abiotic stress responses.

Comprehensive genomic survey, structural classification and expression analysis of C2H2 zinc finger protein gene family in Brassica rapa L

C2H2 zinc finger protein (ZFP) genes have been extensively studied in many organisms and can function as transcription factors and be involved in many biological processes including plant growth and development and stress responses. In the current study, a comprehensive genomics analysis of the C2H2-ZFP genes in B. rapa was performed. A total of 301 B. rapa putative C2H2-ZFP (BrC2H2-ZFP) genes were identified from the available Brassica genome databases, and further characterized through analysis of conserved amino acid residues in C2H2-ZF domains and their organization, subcellular localization, phylogeny, additional domain, chromosomal location, synteny relationship, Ka/Ks ratio, and expression pattern. We also analyzed the expression patterns of eight B. rapa C2H2-ZFP genes under salt and drought stress conditions by using qRT-PCR technique. Our results showed that about one-third of these B. rapa C2H2-ZFP genes were originated from segmental duplication caused by the WGT around 13 to 17 MYA, one-third of them were highly and consecutively expressed in all tested tissues, and 92% of them were located in nucleus by prediction supporting then their functional roles as transcription factors, of which some may play important roles in plant growth and development. The Ka/Ks ratios of 264 orthologous C2H2-ZFP gene pairs between A. thaliana and B. rapa were all, except two, inferior to 1 (varied from 0.0116 to 1.4919, with an average value of 0.3082), implying that these genes had mainly experienced purifying selection during species evolution. The estimated divergence times of the same set of gene pairs ranged from 6.23 to 38.60 MY, with an average value of 18.29 MY, indicating that these gene members have undergone different selective pressures resulting in different evolutionary rates during species evolution. In addition, a few of these B. rapa C2H2-ZFPs were shown to be involved in stress responses in a similar way as their orthologs in A. thaliana. Comparison between A. thaliana and B. rapa orthologous C2H2-ZFP genes showed that the majority of these C2H2-ZFP gene members encodes proteins with conserved subcellular localization and functional domains between the two species but differed in their expression patterns in five tissues or organs. Thus, our study provides valuable information for further functional determination of each C2H2-ZFP gene across the Brassica species, and may help to select the appropriate gene targets for further in-depth studies, and genetic engineering and improvement of Brassica crops.

Ectopic expression of GmZAT4, a putative C2H2-type zinc finger protein, enhances PEG and NaCl stress tolerances in Arabidopsis thaliana

The zinc finger protein (ZFP) transcription factor family plays an important role in regulating plant growth, development, and response to abiotic stress. In this study, we aimed to determine the role of GmZAT4, a C2H2-type transcription factor, in abiotic stress tolerance. The complete coding sequence of the GmZAT4 gene was isolated from soybean root RNA, which shows highest expression level compared with leaf, flower and other tissues. Using multiple sequence alignment and conserved domain analysis, we showed that GmZAT4 is a typical C2H2-type transcription factor which is comprised of two C2H2 domains, including a highly conserved QALGGH motif, and implied the regulation of abiotic stress tolerance in plant. A phylogenetic tree revealed that the soybean GmZAT4 gene clustered with ZAT4 from Glycine soja and AZF1, AZF2, and AZF3 from Arabidopsis thaliana. The mRNA expression levels of GmZAT4 were determined in two soybean cultivars by quantitative reverse transcription (qRT)-PCR and compared. The results showed higher expression (up to 60, 25 and 4 times, respectively) in the drought-tolerant type (Jinda 74) compared to the drought-sensitive soybean cultivar (Jinda 53) following treatment with 18% PEG, 150 mM NaCl, or 100 µM abscisic acid (ABA). GmZAT4 was ectopically over-expressed in A. thaliana to determine its role in abiotic stress tolerance. GmZAT4 overexpression enhanced the tolerance of A. thaliana to treatment with 20% PEG and 150 mM NaCl, and improved the germination rate following treatment with 1 µM or 2 µM ABA. The expression profiles of marker genes in the ABA signaling pathway, such as RD29A, RD29B, ABI, and RAD, indicated that GmZAT4 enhanced the abiotic stress tolerance of Arabidopsis. These results suggest that the C2H2-type ZFP encoded by GmZAT4 plays an important role in PEG and NaCl stress tolerance and ABA responses in soybean and A. thaliana.

The role of C2H2 zinc finger proteins in plant responses to abiotic stresses

Abiotic stresses are important factors affecting plant growth and development and limiting agricultural production worldwide. Plants have evolved complex regulatory mechanisms to respond and adapt to constantly changing environmental conditions. C2H2 zinc finger proteins form a relatively large family of transcriptional regulators in plants. Recent studies have revealed that C2H2 zinc finger proteins function as key transcriptional regulators in plant responses to a wide spectrum of stress conditions, including extreme temperatures, salinity, drought, oxidative stress, excessive light and silique shattering. Here, we summarize recent functional analysis on C2H2 zinc finger proteins in plant responses to abiotic stresses and discuss their roles as part of a large regulatory network in the perception and responses by plants to different environmental stimuli.

A novel Glycine soja homeodomain-leucine zipper (HD-Zip) I gene, Gshdz4, positively regulates bicarbonate tolerance and responds to osmotic stress in Arabidopsis

BACKGROUND

Wild soybean (Glycine soja) is a highly adaptive plant species which can grow well in saline-alkaline soils. In soybean genome, there exist about 140 HD-Zip (Homeodomain-leucine Zipper) genes. HD-Zip transcription factor family is one of the largest plant specific superfamilies and plays important roles in response to abiotic stresses. Although HD-Zip transcription factors have been broadly reported to be involved in plant resistance to abiotic stresses like salt and drought, their roles in response to bicarbonate stress is largely unknown.

RESULTS

From our previous transcriptome profile analysis of wild soybean treated by 50 mM NaHCO3, we identified an HD-Zip gene (Gshdz4) which showed high response to the alkaline stress. Our result of qRT-PCR showed that the expression of Gshdz4 was induced by alkaline stress (NaHCO3) in both leaves and roots of wild soybean. Overexpression of Gshdz4 in Arabidopsis resulted in enhanced tolerance to NaHCO3 and KHCO3 during the process of plant growth and development. However, the growths of transgenic and WT plants were not significantly different on the medium with high pH adjusted by KOH, implicating Gshdz4 is only responsible for resisting HCO3 (-) but not high pH. The transgenic plants had less MDA contents but higher POD activities and chlorophyll contents than the WT plants. Moreover, the transcript levels of stress-related genes, such as NADP-ME, H (+) -Ppase, RD29B and KIN1 were increased with greater extent in the transgenic plants than the wild plants. On the contrary, Gshdz4 overexpression lines were much sensitive to osmotic stress at seed germination and stocking stages compared to the wild plants.

CONCLUSIONS

We revealed that the important and special roles of Gshdz4 in enhancing bicarbonate tolerance and responding to osmotic stress. It is the first time to elucidate these novel functions of HD-ZIP transcription factors. All the evidences broaden our understanding of functions of HD-Zip family and provide clues for uncovering the mechanisms of high tolerance of wild soybean to saline-alkaline stresses.

An Arabidopsis Zinc Finger Protein Increases Abiotic Stress Tolerance by Regulating Sodium and Potassium Homeostasis, Reactive Oxygen Species Scavenging and Osmotic Potential

Plant zinc finger proteins (ZFPs) comprise a large protein family and they are mainly involved in abiotic stress tolerance. Although Arabidopsis RING/FYVE/PHD ZFP At5g62460 (AtRZFP) is found to bind to zinc, whether it is involved in abiotic stress tolerance is still unknown. In the present study, we characterized the roles of AtRZFP in response to abiotic stresses. The expression of AtRZFP was induced significantly by salt and osmotic stress. AtRZFP positively mediates tolerance to salt and osmotic stress. Additionally, compared with wild-type Arabidopsis plants, plants overexpressing AtRZFP showed reduced reactive oxygen species (ROSs) accumulation, enhanced superoxide dismutase and peroxidase activity, increased soluble sugars and proline contents, reduced K(+) loss, decreased Na(+) accumulation, stomatal aperture and the water loss rate. Conversely, AtRZFP knockout plants displayed the opposite physiological changes when exposed to salt or osmotic stress conditions. These data suggested that AtRZFP enhances salt and osmotic tolerance through a series of physiological processes, including enhanced ROSs scavenging, maintaining Na(+) and K(+) homeostasis, controlling the stomatal aperture to reduce the water loss rate, and accumulating soluble sugars and proline to adjust the osmotic potential.

Soybean C2H2-Type Zinc Finger Protein GmZFP3 with Conserved QALGGH Motif Negatively Regulates Drought Responses in Transgenic Arabidopsis

Plant response to environmental stresses is regulated by a complicated network of regulatory and functional genes. In this study, we isolated the putative stress-associated gene GmZFP3 (a C2H2-type Zinc finger protein gene) based on the previous finding that it was one of two genes located in the QTL region between the Satt590 and Satt567 markers related to soybean tolerance to drought. Temporal and spatial expression analysis using quantitative real-time PCR indicated that GmZFP3 was primarily expressed in roots, stems and leaf organs and was expressed at low levels in flowers and soybean pods. Moreover, GmZFP3 expression increased in response to polyethylene glycol (PEG) and Abscisic acid (ABA) treatments. In addition, subcellular localization analysis indicated that GmZFP3 was ubiquitously distributed in plant cells. Transgenic experiments indicated that GmZFP3 played a negative role in plant tolerance to drought. Analysis of ABA-related marker gene expression in Arabidopsis suggested that GmZFP3 might be involved in the ABA-dependent pathway during the drought stress response. Taken together, these results suggest that soybean GmZFP3 negatively regulates the drought response.

Quantitative iTRAQ-based proteomic analysis of phosphoproteins and ABA-regulated phosphoproteins in maize leaves under osmotic stress

Abscisic acid (ABA) regulates various developmental processes and stress responses in plants. Protein phosphorylation/dephosphorylation is a central post-translational modification (PTM) in ABA signaling. However, the phosphoproteins regulated by ABA under osmotic stress remain unknown in maize. In this study, maize mutant vp5 (deficient in ABA biosynthesis) and wild-type Vp5 were used to identify leaf phosphoproteins regulated by ABA under osmotic stress. Up to 4052 phosphopeptides, corresponding to 3017 phosphoproteins, were identified by Multiplex run iTRAQ-based quantitative proteomic and LC-MS/MS methods. The 4052 phosphopeptides contained 5723 non-redundant phosphosites; 512 phosphopeptides (379 in Vp5, 133 in vp5) displayed at least a 1.5-fold change of phosphorylation level under osmotic stress, of which 40 shared common in both genotypes and were differentially regulated by ABA. Comparing the signaling pathways involved in vp5 response to osmotic stress and those that in Vp5, indicated that ABA played a vital role in regulating these pathways related to mRNA synthesis, protein synthesis and photosynthesis. Our results provide a comprehensive dataset of phosphopeptides and phosphorylation sites regulated by ABA in maize adaptation to osmotic stress. This will be helpful to elucidate the ABA-mediate mechanism of maize endurance to drought by triggering phosphorylation or dephosphorylation cascades.

GhWRKY68 reduces resistance to salt and drought in transgenic Nicotiana benthamiana

The WRKY transcription factors modulate numerous physiological processes, including plant growth, development and responses to various environmental stresses. Currently, our understanding of the functions of the majority of the WRKY family members and their possible roles in signalling crosstalk is limited. In particular, very few WRKYs have been identified and characterised from an economically important crop, cotton. In this study, we characterised a novel group IIc WRKY gene, GhWRKY68, which is induced by different abiotic stresses and multiple defence-related signalling molecules. The β-glucuronidase activity driven by the GhWRKY68 promoter was enhanced after exposure to drought, salt, abscisic acid (ABA) and H2O2. The overexpression of GhWRKY68 in Nicotiana benthamiana reduced resistance to drought and salt and affected several physiological indices. GhWRKY68 may mediate salt and drought responses by modulating ABA content and enhancing the transcript levels of ABA-responsive genes. GhWRKY68-overexpressing plants exhibited reduced tolerance to oxidative stress after drought and salt stress treatments, which correlated with the accumulation of reactive oxygen species (ROS), reduced enzyme activities, elevated malondialdehyde (MDA) content and altered ROS-related gene expression. These results indicate that GhWRKY68 is a transcription factor that responds to drought and salt stresses by regulating ABA signalling and modulating cellular ROS.

Identification of rice Di19 family reveals OsDi19-4 involved in drought resistance

The OsDi19 proteins functioned as transcription factors and played crucial roles in response to abiotic stress. Overexpression of OsDi19-4 in rice increased drought tolerance by enhancing ROS-scavenging activity. Many transcription factors play crucial roles in plant responses to abiotic stress. Here, comprehensive sequence analysis suggested that the drought-induced 19 (Di19) gene family in rice genome contain seven members, and these proteins contained a well-conserved zinc-finger Di19 domain. Most OsDi19 proteins were mainly targeted to the nucleus and have transactivation activity in yeast. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that most OsDi19 proteins could form protein dimers. Expression analysis demonstrated that the OsDi19 genes were differentially and abundantly expressed in vegetative tissues, but expressed little in reproductive tissues and some of the OsDi19 genes were markedly induced by abiotic stresses and hormones in qRT-PCR analysis and microarray data. Overexpression of one stress-responsive gene, OsDi19-4, in rice resulted in significantly increased tolerance to drought stress compared with the wild type plants. Moreover, obviously increased ROS-scavenging ability was detected in the OsDi19-4-overexpressing plants under normal and drought stress conditions. These results suggested that the increased stress tolerance of OsDi19-4-overexpressing plants may be attributable to the enhanced ROS-scavenging activity. Taken together, these studies provide a detailed overview of the rice Di19 gene family, and suggest that the OsDi19 family may play crucial roles in the plant response to abiotic stress.

The cotton WRKY transcription factor GhWRKY17 functions in drought and salt stress in transgenic Nicotiana benthamiana through ABA signaling and the modulation of reactive oxygen species production

Drought and high salinity are two major environmental factors that significantly limit the productivity of agricultural crops worldwide. WRKY transcription factors play essential roles in the adaptation of plants to abiotic stresses. However, WRKY genes involved in drought and salt tolerance in cotton (Gossypium hirsutum) are largely unknown. Here, a group IId WRKY gene, GhWRKY17, was isolated and characterized. GhWRKY17 was found to be induced after exposure to drought, salt, H2O2 and ABA. The constitutive expression of GhWRKY17 in Nicotiana benthamiana remarkably reduced plant tolerance to drought and salt stress, as determined through physiological analyses of the germination rate, root growth, survival rate, leaf water loss and Chl content. GhWRKY17 transgenic plants were observed to be more sensitive to ABA-mediated seed germination and root growth. However, overexpressing GhWRKY17 in N. benthamiana impaired ABA-induced stomatal closure. Furthermore, we found that GhWRKY17 modulated the increased sensitivity of plants to drought by reducing the level of ABA, and transcript levels of ABA-inducible genes, including AREB, DREB, NCED, ERD and LEA, were clearly repressed under drought and salt stress conditions. Consistent with the accumulation of reactive oxygen species (ROS), reduced proline contents and enzyme activities, elevated electrolyte leakage and malondialdehyde, and lower expression of ROS-scavenging genes, including APX, CAT and SOD, the GhWRKY17 transgenic plants exhibited reduced tolerance to oxidative stress compared with wild-type plants. These results therefore indicate that GhWRKY17 responds to drought and salt stress through ABA signaling and the regulation of cellular ROS production in plants.

Molecular characterization of cotton C-repeat/dehydration-responsive element binding factor genes that are involved in response to cold stress

Low temperature, drought and salinity are major abiotic stresses that influence survival, productivity and geographical distribution of many important crops across the globe. The C-repeat/dehydration-responsive element binding transcription factors (CBF/DREB) are important proteins involved in response to abiotic stresses in plants. In this study, twenty-one CBF genes were identified in cotton (Gossypium hirsutum) by bioinformatic approach. The twenty-one CBF genes (named as GhCBF1--GhCBF21) were characterized to encode proteins that share high similarity with those plant cold stress-related CBF proteins, which contain the classic AP2 domain of 58 amino acid residues. Phylogenetic analysis revealed that the isolated cotton CBF genes can be classified into 4 groups: GhCBF I, GhCBF II, GhCBF III and GhCBF IV. RT-PCR analysis indicated that GhCBF genes were up-regulated in cotton plants under cold stress. Furthermore, four GhCBF genes were up-regulated in cotton under salinity and drought treatments. Our data provided valuable information for further exploring the roles of the CBF genes in cotton development and in response to cold stress.

Overexpression of GsZFP1 enhances salt and drought tolerance in transgenic alfalfa (Medicago sativa L.)

GsZFP1 encodes a Cys2/His2-type zinc-finger protein. In our previous study, when GsZFP1 was heterologously expressed in Arabidopsis, the transgenic Arabidopsis plants exhibited enhanced drought and cold tolerance. However, it is still unknown whether GsZFP1 is also involved in salt stress. GsZFP1 is from the wild legume Glycine soja. Therefore, the aims of this study were to further elucidate the functions of the GsZFP1 gene under salt and drought stress in the forage legume alfalfa and to investigate its biochemical and physiological functions under these stress conditions. Our data showed that overexpression of GsZFP1 in alfalfa resulted in enhanced salt tolerance. Under high salinity stress, greater relative membrane permeability and malondialdehyde (MDA) content were observed and more free proline and soluble sugars accumulated in transgenic alfalfa than in the wild-type (WT) plants; in addition, the transgenic lines accumulated less Na(+) and more K(+) in both the shoots and roots. Overexpression of GsZFP1 also enhanced the drought tolerance of alfalfa. The fold-inductions of stress-responsive marker gene expression, including MtCOR47, MtRAB18, MtP5CS, and MtRD2, were greater in transgenic alfalfa than those of WT under drought stress conditions. In conclusion, the transgenic alfalfa plants generated in this study could be used for farming in salt-affected as well as arid and semi-arid areas.

Ectopic expression of a WRKY homolog from Glycine soja alters flowering time in Arabidopsis

Flowering is a critical event in the life cycle of plants; the WRKY-type transcription factors are reported to be involved in many developmental processes sunch as trichome development and epicuticular wax loading, but whether they are involved in flowering time regulation is still unknown. Within this study, we provide clear evidence that GsWRKY20, a member of WRKY gene family from wild soybean, is involved in controlling plant flowering time. Expression of GsWRKY20 was abundant in the shoot tips and inflorescence meristems of wild soybean. Phenotypic analysis showed that GsWRKY20 over-expression lines flowered earlier than the wild-type plants under all conditions: long-day and short-day photoperiods, vernalization, or exogenous GA3 application, indicating that GsWRKY20 may mainly be involved in an autonomous flowering pathway. Further analyses by qRT-PCR and microarray suggests that GsWRKY20 accelerating plant flowering might primarily be through the regulation of flowering-related genes (i.e., FLC, FT, SOC1 and CO) and floral meristem identity genes (i.e., AP1, SEP3, AP3, PI and AG). Our results provide the evidence demonstrating the effectiveness of manipulating GsWRKY20 for altering plant flowering time.