Zinc finger protein 1 (ThZF1) from salt cress (Thellungiella halophila) is a Cys-2/His-2-type transcription factor involved in drought and salt stress

A 21-bp InDel in the promoter of STP1 selected during tomato improvement accounts for soluble solid content in fruits

Domestication and improvement are important processes that generate the variation in genome and phonotypes underlying crop improvement. Unfortunately, during selection for certain attributes, other valuable traits may be inadvertently discarded. One example is the decline in fruit soluble solids content (SSC) during tomato breeding. Several genetic loci for SSC have been identified, but few reports on the underlying mechanisms are available. In this study we performed a genome-wide association study (GWAS) for SSC of the red-ripe fruits in a population consisting of 481 tomato accessions with large natural variations and found a new quantitative trait locus, STP1, encoding a sugar transporter protein. The causal variation of STP1, a 21-bp InDel located in the promoter region 1124 bp upstream of the start codon, alters its expression. STP1 ^Insertion accessions with an 21-bp insertion have higher SSC than STP1 ^Deletion accessions with the 21-bp deletion. Knockout of STP1 in TS-23 with high SSC using CRISPR/Cas9 greatly decreased SSC in fruits. In vivo and in vitro assays demonstrated that ZAT10-LIKE, a zinc finger protein transcription factor (ZFP TF), can specifically bind to the promoter of STP1 ^Insertion to enhance STP1 expression, but not to the promoter of STP1 ^Deletion , leading to lower fruit SSC in modern tomatoes. Diversity analysis revealed that STP1 was selected during tomato improvement. Taking these results together, we identified a naturally occurring causal variation underlying SSC in tomato, and a new role for ZFP TFs in regulating sugar transporters. The findings enrich our understanding of tomato evolution and domestication, and provide a genetic basis for genome design for improving fruit taste.

Genome-wide characterization of C2H2 zinc-finger gene family provides insight into the mechanisms and evolution of the dehydration-rehydration responses in Physcomitrium and Arabidopsis

Dehydration tolerance is a vital factor for land plant evolution and world agricultural production. Numerous studies enlightened that the plant-specific C2H2-type zinc-finger proteins (C2H2-ZFPs) as master regulators played pivotal roles in the abiotic stress responses of plants. However, a comprehensive understanding of the evolution of C2H2-ZFPs in terrestrial plants and its regulatory mechanism in dehydration and rehydration response remains a mystery. In this study, the genome-wide identification of C2H2-ZFP genes revealed 549 homologs in the representatives of terrestrial plant lineages from liverwort to angiosperms. Based on the characteristics of the conserved C2H2-ZF domains, four major C2H2-ZF types (M-, Z-, Q-, and D-type) were identified in the C2H2-ZFPs, with the dominants of M-type in all selected species and followed by Z-type in non-seed plants and Q-type in seed plants, respectively. Phylogenetic analyses of the identified C2H2-ZFPs supported four major groups in the land plant representatives, among which the members from the desiccation-tolerant Physcomitrium patens and the dehydration-sensitive Arabidopsis thaliana displayed different topological relationships in the phylogenies reconstructed for a single species. C2H2-ZFPs clustered in the same subclades shared similar features in their conserved domains and gene structures. Approximately, 81% of the C2H2-ZFP promoters of all 549 identified C2H2-ZFPs harbored the conserved ABA-responsive elements (ABREs) and/or dehydration-responsive elements (DREs). Comparative transcriptomic analyses showed that 50 PpZFPs and 56 AtZFPs significantly changed their transcripts abundance. Interestingly, most of the dehydration- and rehydration-responsive PpZPFs and AtZFPs had been predicted to contain the ABRE and DRE elements in their promoter regions and with over half of which phylogenetically belonging to group III. The differences in the expression patterns of C2H2-ZFPs in responses to dehydration and rehydration between P. patens and A. thaliana reflected their different strategies to adapt to dehydration. The identified candidate PpZFPs were specifically induced by moderate dehydration and reached the peak transcript abundance in severe dehydration. Our study lays the foundations for further functional investigation of C2H2-ZFPs in dehydration responses from an evolutionary perspective in land plants. The findings will provide us with genetic resources and potential targets for drought tolerance breeding in crops and beyond.

In Silico Functional Prediction and Expression Analysis of C2H2 Zinc-Finger Family Transcription Factor Revealed Regulatory Role of ZmZFP126 in Maize Growth

The C2H2-zinc finger proteins (ZFP) comprise a large family of transcription factors with various functions in biological processes. In maize, the function regulation of C2H2- zine finger (ZF) genes are poorly understood. We conducted an evolution analysis and functional prediction of the maize C2H2-ZF gene family. Furthermore, the ZmZFP126 gene has been cloned and sequenced for further favorable allelic variation discovery. The phylogenetic analysis of the C2H2-ZF domain indicated that the position and sequence of the C2H2-ZF domain of the poly-zinc finger gene are relatively conserved during evolution, and the C2H2-ZF domain with the same position is highly conserved. The expression analysis of the C2H2-ZF gene family in 11 tissues at different growth stages of B73 inbred lines showed that genes with multiple transcripts were endowed with more functions. The expression analysis of the C2H2-ZF gene in P1 and P2 inbred lines under drought conditions showed that the C2H2-ZF genes were mainly subjected to negative regulation under drought stress. Functional prediction indicated that the maize C2H2-ZF gene is mainly involved in reproduction and development, especially concerning the formation of important agronomic traits in maize yield. Furthermore, sequencing and correlation analysis of the ZmZFP126 gene indicated that this gene was significantly associated with the SDW-NAP and TDW-NAP. The analysis of the relationship between maize C2H2-ZF genes and C2H2-ZF genes with known functions indicated that the functions of some C2H2-ZF genes are relatively conservative, and the functions of homologous genes in different species are similar.

The role of VvMYBA2r and VvMYBA2w alleles of the MYBA2 locus in the regulation of anthocyanin biosynthesis for molecular breeding of grape (Vitis spp.) skin coloration

In grape, MYBA1 and MYBA2 at the colour locus are the major genetic determinants of grape skin colour, and the mutation of two functional genes (VvMYBA1 and VvMYBA2) from these loci leads to white skin colour. This study aimed to elucidate the regulation of grape berry coloration by isolating and characterizing VvMYBA2w and VvMYBA2r alleles. The overexpression of VvMYBA2r up-regulated the expression of anthocyanin biosynthetic genes and resulted in higher anthocyanin accumulation in transgenic tobacco than wild-type (WT) plants, especially in flowers. However, the ectopic expression of VvMYBA2w inactivated the expression of anthocyanin biosynthetic genes and could not cause obvious phenotypic modulation in transgenic tobacco. Unlike in VvMYBA2r, CA dinucleotide deletion shortened the C-terminal transactivation region and disrupted the transcriptional activation activity of VvMYBA2w. The results indicated that VvMYBA2r positively regulated anthocyanin biosynthesis by forming the VvMYBA2r-VvMYCA1-VvWDR1 complex, and VvWDR1 enhanced anthocyanin accumulation by interacting with the VvMYBA2r-VvMYCA1 complex; however, R⁴⁴ L substitution abolished the interaction of VvMYBA2w with VvMYCA1. Meanwhile, both R⁴⁴ L substitution and CA dinucleotide deletion seriously affected the efficacy of VvMYBA2w to regulate anthocyanin biosynthesis, and the two non-synonymous mutations were additive in their effects. Investigation of the colour density and MYB haplotypes of 213 grape germplasms revealed that dark-skinned varieties tended to contain HapC-N and HapE2, whereas red-skinned varieties contained high frequencies of HapB and HapC-Rs. Regarding ploidy, the higher the number of functional alleles present in a variety, the darker was the skin colour. In summary, this study provides insight into the roles of VvMYBA2r and VvMYBA2w alleles and lays the foundation for the molecular breeding of grape varieties with different skin colour.

Drought-induced protein (Di19-3) plays a role in auxin signaling by interacting with IAA14 in Arabidopsis

The members of early auxin response gene family, Aux/IAA, encode negative regulators of auxin signaling but play a central role in auxin-mediated plant development. Here we report the interaction of an Aux/IAA protein, AtIAA14, with Drought-induced-19 (Di19-3) protein and its possible role in auxin signaling. The Atdi19-3 mutant seedlings develop short hypocotyl, both in light and dark, and are compromised in temperature-induced hypocotyl elongation. The mutant plants accumulate more IAA and also show altered expression of NIT2, ILL5, and YUCCA genes involved in auxin biosynthesis and homeostasis, along with many auxin responsive genes like AUX1 and MYB77. Atdi19-3 seedlings show enhanced root growth inhibition when grown in the medium supplemented with auxin. Nevertheless, number of lateral roots is low in Atdi19-3 seedlings grown on the basal medium. We have shown that AtIAA14 physically interacts with AtDi19-3 in yeast two-hybrid (Y2H), bimolecular fluorescence complementation, and in vitro pull-down assays. However, the auxin-induced degradation of AtIAA14 in the Atdi19-3 seedlings was delayed. By expressing pIAA14::mIAA14-GFP in Atdi19-3 mutant background, it became apparent that both Di19-3 and AtIAA14 work in the same pathway and influence lateral root development in Arabidopsis. Gain-of-function slr-1/iaa14 (slr) mutant, like Atdi19-3, showed tolerance to abiotic stress in seed germination and cotyledon greening assays. The Atdi19-3 seedlings showed enhanced sensitivity to ethylene in triple response assay and AgNO3, an ethylene inhibitor, caused profuse lateral root formation in the mutant seedlings. These observations suggest that AtDi19-3 interacting with AtIAA14, in all probability, serves as a positive regulator of auxin signaling and also plays a role in some ethylene-mediated responses in Arabidopsis.

SIGNIFICANCE STATEMENT

This study has demonstrated interaction of auxin responsive Aux/IAA with Drought-induced 19 (Di19) protein and its possible implication in abiotic stress response.

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.

Ionomic and metabolomic analyses reveal the resistance response mechanism to saline-alkali stress in Malus halliana seedlings

Saline-alkali stress is a major abiotic stress limiting plant growth. The selection of saline-alkali-tolerant rootstock is an effective strategy to reduce salinization-alkalization influence in apple production. M. halliana is a highly saline-alkali-resistant apple rootstock in northwestern China. However, few metabolic response studies have been conducted on this species. In plants under saline-alkali stress, the uptake of K, Mg and Zn in M. halliana leaves were inhibited, whereas the absorption of Fe²⁺, Cu²⁺ or Mn²⁺ were increased. Metabolic analysis revealed 140 differentially expressed metabolites, which were mainly involved in alkaloid biosynthesis, phenylalanine biosynthesis, ATP-binding cassette (ABC) transporters, and mineral absorption. Especially, the expression of sucrose, amino acids, alkaloids, flavonoids and carotenoids were significantly upregulated under saline-alkali stress. qRT-PCR analysis demonstrated that NHX8 and ZTP1 involved in Na⁺ and Fe²⁺ transport were upregulated, while AKT1, MRS2-4 and ZTP29 involved in K⁺, Mg²⁺ and Zn²⁺ transport were downregulated, respectively. ANT, ATP2A, CALM and SOS2 are involved in Ca²⁺ signal transduction, and ABCB1, ABCC10 and NatA are key transporters that maintain ionic homeostasis. M. halliana regulates Na⁺/K⁺ homeostasis by mediating Ca²⁺ signalling and ABC transporters. The accumulation of metabolites contributes to improving the saline-alkali resistance of M. halliana because of the scavenging of ROS. An increase in pheophorbide a content in porphyrin and chlorophyll metabolism leads to leaf senescence in M. halliana leaves, which contributes to a reduction in stress-induced injury. These findings provide important insights into the saline-alkali tolerance mechanism in apple, which also provides an important starting point for future research.

Functional characterisation of two phytochelatin synthases in rice (Oryza sativa cv. Milyang 117) that respond to cadmium stress

Cadmium (Cd) is one of the most toxic heavy metals and a non-essential element to all organisms, including plants; however, the genes involved in Cd resistance in plants remain poorly characterised. To identify Cd resistance genes in rice, we screened a rice cDNA expression library treated with CdCl₂ using a yeast (Saccharomyces cerevisiae) mutant ycf1 strain (DTY167) and isolated two rice phytochelatin synthases (OsPCS5 and OsPCS15). The genes were strongly induced by Cd treatment and conferred increased resistance to Cd when expressed in the ycf1 mutant strain. In addition, the Cd concentration was twofold higher in yeast expressing OsPCS5 and OsPCS15 than in vector-transformed yeast, and OsPCS5 and OsPCS15 localised in the cytoplasm. Arabidopsis thaliana plants overexpressing OsPCS5/-15 paradoxically exhibited increased sensitivity to Cd, suggesting that overexpression of OsPCS5/-15 resulted in toxicity due to excess phytochelatin production in A. thaliana. These data indicate that OsPCS5 and OsPCS15 are involved in Cd tolerance, which may be related to the relative abundances of phytochelatins synthesised by these phytochelatin synthases.

AtSIZ1 improves salt tolerance by maintaining ionic homeostasis and osmotic balance in Arabidopsis

C2H2-type zinc finger proteins play important roles in plant growth, development, and abiotic stress tolerance. Here, we explored the role of the C2H2-type zinc finger protein SALT INDUCED ZINC FINGER PROTEIN1 (AtSIZ1; At3G25910) in Arabidopsis thaliana under salt stress. AtSIZ1 expression was induced by salt treatment. During the germination stage, the germination rate, germination energy, germination index, cotyledon growth rate, and root length were significantly higher in AtSIZ1 overexpression lines than in the wild type under various stress treatments, whereas these indices were significantly reduced in AtSIZ1 loss-of-function mutants. At the mature seedling stage, the overexpression lines maintained higher levels of K⁺, proline, and soluble sugar, lower levels of Na⁺ and MDA, and lower Na⁺/K⁺ ratios than the wild type. Stress-related marker genes such as SOS1, AtP5CS1, AtGSTU5, COR15A, RD29A, and RD29B were expressed at higher levels in the overexpression lines than the wild type and loss-of-function mutants under salt treatment. These results indicate that AtSIZ1 improves salt tolerance in Arabidopsis by helping plants maintain ionic homeostasis and osmotic balance.

Cold-inducible MaC2H2s are associated with cold stress response of banana fruit via regulating MaICE1

MaC2H2s are involved in cold stress response of banana fruit via repressing the transcription of MaICE1. Although C2H2 zinc finger proteins have been found to be involved in banana fruit ripening through transcriptional controlling of ethylene biosynthetic genes, their involvement in cold stress of banana remains elusive. In this study, another C2H2-ZFP gene from banana fruit was identified, which was named as MaC2H2-3. Gene expression analysis revealed that MaC2H2-1, MaC2H2-2 and MaC2H2-3 were cold inducible in the peel of banana during low temperature storage. MaC2H2-3 functions as a transcriptional repressor and localizes predominantly in nucleus. Particularly, promoters of MaC2H2-2 and MaC2H2-3 were noticeably activated by cold as well, further indicating the potential roles of C2H2 in cold stress of banana. Moreover, MaC2H2-2 and MaC2H2-3 significantly repressed the transcription of MaICE1, a key component in cold signaling pathway. Overall, these findings suggest that MaC2H2s may take part in controlling cold stress of banana through suppressing the transcription of MaICE1, providing new insight of the regulatory basis of C2H2 in cold stress.

TaZFP1, a C2H2 type-ZFP gene of T. aestivum, mediates salt stress tolerance of plants by modulating diverse stress-defensive physiological processes

Salt stress suppresses plant growth, development, and crop productivity. In this study, we characterized the role of TaZFP1, a C2H2 type-zinc finger protein family member of T. aestivum, in salt stress tolerance. TaZFP1 possesses a conserved C2H2 motif (CX2-4CX12HX3-5H) shared by plant ZFP proteins, translocates to the nucleus after endoplasmic reticulum (ER) assortment, and displays a ZF 3-D structure similar to its eukaryote homologs. The transcripts of TaZFP1 were upregulated during salt stress condition and this effect was restored under normal conditions. Compared to wild type (WT), the transgenic lines of TaZFP1 overexpression or knockdown displayed improved phenotypes, biomass, photosynthesis parameters (Pn, ΨPSII, and NPQ), osmolytes contents (i.e. proline and soluble sugar), and enhanced antioxidant enzyme (AE) activity following salt stress treatment. A set of genes associated with proline synthesis (i.e., NtP5CS1 and NtP5CS2) and encoding AEs (i.e., NtSOD2, NtCAT1, and NtPOD4) were upregulated in the salt-challenged transgenic lines of TaZFP1 expression. Additionally, the transgenic lines exhibited similar stomata movement patterns and leaf water retention properties under salinity conditions compared to those induced by exogenous abscisic acid (ABA) treatment, suggesting that the TaZFP1-mediated salt response is dependent on the ABA signaling. High throughput RNAseq analysis revealed significant alteration of gene transcription in transgenic lines upon salt stress. Among them, the differentially expressed genes (DEGs) represented by the gene ontology (GO) terms were associated with organic acid, carboxylic acid, carbohydrate, and coenzyme as well as organonitrogen compounds, translation, peptide metabolism, and peptide biosynthesis. A set of upregulated DEGs were found to be thylakoid- and photosystem-associated, which is consistent with the TaZFP1-mediated improvement in photosynthesis in salt-stressed transgenic lines. Our investigation indicated that the TaZFP1-mediated salt tolerance is ascribed to the regulation of gene functions related to photosynthesis, osmolytes metabolism and ROS homeostasis mediated by ABA signaling.

Ectopic Expression of a Thellungiella salsuginea Aquaporin Gene, TsPIP1;1, Increased the Salt Tolerance of Rice

Aquaporins play important regulatory roles in the transport of water and small molecules in plants. In this study, a Thellungiella salsuginea TsPIP1;1 aquaporin was transformed into Kitaake rice, and three transgenic lines were evaluated by profiling the changes of the physiological metabolism, osmotic potential, and differentially expressed genes under salt stress. The TsPIP1;1 protein contains six transmembrane domains and is localized in the cytoplasm membrane. Overexpression of the TsPIP1;1 gene not only increased the accumulation of prolines, soluble sugars and chlorophyll, but also lowered the osmotic potential and malondialdehyde content in rice under salt stress, and alleviated the amount of salt damage done to rice organs by regulating the distribution of Na/K ions, thereby promoting photosynthetic rates. Transcriptome sequencing confirmed that the differentially expressed genes that are up-regulated in rice positively respond to salt stimulus, the photosynthetic metabolic process, and the accumulation profiles of small molecules and Na/K ions. The co-expressed Rubisco and LHCA4 genes in rice were remarkably up-regulated under salt stress. This data suggests that overexpression of the TsPIP1;1 gene is involved in the regulation of water transport, the accumulation of Na/K ions, and the translocation of photosynthetic metabolites, thus conferring enhanced salt tolerance to rice.

Knockdown of an inflorescence meristem-specific cytokinin oxidase - OsCKX2 in rice reduces yield penalty under salinity stress condition

Cytokinins play a significant role in determining grain yield in plants. Cytokinin oxidases catalyse irreversible degradation of cytokinins and hence modulate cellular cytokinin levels. Here, we studied the role of an inflorescence meristem-specific rice cytokinin oxidase - OsCKX2 - in reducing yield penalty under salinity stress conditions. We utilized an RNAi-based approach to study the function of OsCKX2 in maintaining grain yield under salinity stress condition. Ultra-performance liquid chromatography-based estimation revealed a significant increase in cytokinins in the inflorescence meristem of OsCKX2-knockdown plants. To determine if there exists a correlation between OsCKX2 levels and yield under salinity stress condition, we assessed the growth, physiology and grain yield of OsCKX2-knockdown plants vis-à-vis the wild type. OsCKX2-knockdown plants showed better vegetative growth, higher relative water content and photosynthetic efficiency and reduced electrolyte leakage as compared with the wild type under salinity stress. Importantly, we found a negative correlation between OsCKX2 expression and plant productivity as evident by assessment of agronomical parameters such as panicle branching, filled grains per plant and harvest index both under control and salinity stress conditions. These results suggest that OsCKX2, via controlling cytokinin levels, regulates floral primordial activity modulating rice grain yield under normal as well as abiotic stress conditions.

Molecular cloning and characterization of PtrZPT2-1, a ZPT2 family gene encoding a Cys2/His2-type zinc finger protein from trifoliate orange (Poncirus trifoliata (L.) Raf.) that enhances plant tolerance to multiple abiotic stresses

In plants, most Cys2/His2 (C2H2) zinc finger proteins with two zinc finger domains (ZPT2) are involved in abiotic stress responses. In this study, a ZPT2 family gene PtrZPT2-1 was cloned from trifoliate orange (Poncirus trifoliata (L.) Raf.). PtrZPT2-1 is composed of 245 amino acids, has a putative molecular weight of 25.99kDa and an isoelectric point of 8.41. PtrZPT2-1 contained two C2H2 zinc finger domains, one nuclear localization signal (B-box), one transcription repression domain (DLN-box), and one protein-protein interaction domain (L-box). PtrZPT2-1 was localized to the nucleus. The PtrZPT2-1 expression was strongly induced by cold, drought, salt and ABA stresses. Overexpression of PtrZPT2-1 increased the survival rates, and the ABA, soluble sugar and proline levels but decreased the ion leakage, the malondialdehyde (MDA) content and reduced the H2O2 accumulation in the transgenic tobacco after cold, drought or salt treatments. Furthermore, the expression levels of 15 abiotic stress-related genes were significantly increased in the transgenic tobacco overexpressing PtrZPT2-1 after cold, drought or salt stress treatments. Our results indicated that overexpression of PtrZPT2-1 in the transgenic tobacco could improve the cold, drought and salt resistance of the plants by increasing the levels of osmotic regulatory solutes and decreasing the accumulation of H2O2.

The Arabidopsis Cys2/His2 zinc finger transcription factor ZAT18 is a positive regulator of plant tolerance to drought stress

Environmental stress poses a global threat to plant growth and reproduction, especially drought stress. Zinc finger proteins comprise a family of transcription factors that play essential roles in response to various abiotic stresses. Here, we found that ZAT18 (At3g53600), a nuclear C2H2 zinc finger protein, was transcriptionally induced by dehydration stress. Overexpression (OE) of ZAT18 in Arabidopsis improved drought tolerance while mutation of ZAT18 resulted in decreased plant tolerance to drought stress. ZAT18 was preferentially expressed in stems, siliques, and vegetative rosette leaves. Subcellular location results revealed that ZAT18 protein was predominantly localized in the nucleus. ZAT18 OE plants exhibited less leaf water loss, lower content of reactive oxygen species (ROS), higher leaf water content, and higher antioxidant enzyme activities after drought treatment when compared with the wild type (WT). RNA sequencing analysis showed that 423 and 561 genes were transcriptionally modulated by the ZAT18 transgene before and after drought treatment, respectively. Pathway enrichment analysis indicated that hormone metabolism, stress, and signaling were over-represented in ZAT18 OE lines. Several stress-responsive genes including COR47, ERD7, LEA6, and RAS1, and hormone signaling transduction-related genes including JAZ7 and PYL5 were identified as putative target genes of ZAT18. Taken together, ZAT18 functions as a positive regulator and plays a crucial role in the plant response to drought stress.

The Arabidopsis Gene zinc finger protein 3(ZFP3) Is Involved in Salt Stress and Osmotic Stress Response

Plants are continuously challenged by various abiotic and biotic stresses. To tide over these adversities, plants evolved intricate regulatory networks to adapt these unfavorable environments. So far, many researchers have clarified the molecular and genetic pathways involved in regulation of stress responses. However, the mechanism through which these regulatory networks operate is largely unknown. In this study, we cloned a C₂H₂-type zinc finger protein gene ZFP3 from Arabidopsis thaliana and investigated its function in salt and osmotic stress response. Our results showed that the expression level of ZFP3 was highly suppressed by NaCl, mannitol and sucrose. Constitutive expression of ZFP3 enhanced tolerance of plants to salt and osmotic stress while the zfp3 mutant plants displays reduced tolerance in Arabidopsis. Gain- and Loss-of-function studies of ZFP3 showed that ZFP3 significantly changes proline accumulation and chlorophyll content. Furthermore, over-expression of ZFP3 induced the expressions of stress-related gene KIN1, RD22, RD29B and AtP5CS1. These results suggest that ZFP3 is involved in salt and osmotic stress response.

NbCZF1, a Novel C2H2-Type Zinc Finger Protein, as a New Regulator of SsCut-Induced Plant Immunity in Nicotiana benthamiana

SsCut, which functions as an elicitor, can induce plant immunity. In this study, we utilized Nicotiana benthamiana and virus-induced gene silencing to decrease the expression of > 2,500 genes individually. Using this forward genetics approach, several genes were identified that, when silenced, compromised SsCut-triggered cell death based on a cell death assay. A C2H2-type zinc finger gene was isolated from N. benthamiana Sequence analysis indicated that the gene encodes a 27 kDa protein with 253 amino acids containing two typical C2H2-type zinc finger domains; this gene was named NbCZF1 We found that SsCut-induced cell death could be inhibited by virus-induced gene silencing of NbCZF1 in N. benthamiana In addition, SsCut induces stomatal closure, accompanied by reactive oxygen species (ROS) production by NADPH oxidases and nitric oxide (NO) production. NbCZF1-silenced plants showed impaired SsCut-induced stomatal closure, decreased SsCut-induced production of ROS and NO in guard cells and reduced SsCut-induced resistance against Phytophthora nicotianae Taken together, these results demonstrate that the NbCZF1-ROS-NO pathway mediates multiple SsCut-triggered responses, including stomatal closure, hypersensitive responses and defense-related gene expression. This is the first report describing the function of a C2H2-type zinc finger protein in N. benthamiana.

Phosphorylation of serine residue modulates cotton Di19-1 and Di19-2 activities for responding to high salinity stress and abscisic acid signaling

Di19 (drought-induced protein 19) family is a novel type of Cys2/His2 zinc-finger proteins. In this study, we demonstrated that cotton Di19-1 and Di19-2 (GhDi19-1/-2) proteins could be phosphorylated in vitro by the calcium-dependent protein kinase (CDPK). Mutation of Ser to Ala in N-terminus of GhDi19-1/-2 led to the altered subcellular localization of the two proteins, but the constitutively activated form (Ser was mutated to Asp) of GhDi19-1/-2 still showed the nuclear localization. GhDi19-1/-2 overexpression transgenic Arabidopsis seedlings displayed the hypersensitivity to high salinity and abscisic acid (ABA). However, Ser site-mutated GhDi19-1(S116A) and GhDi19-2(S114A), and Ser and Thr double sites-mutated GhDi19-1(S/T-A/A) and GhDi19-2(S/T-A/A) transgenic Arabidopsis did not show the salt- and ABA-hypersensitive phenotypes. In contrast, overexpression of Thr site-mutated GhDi19-1(T114A) and GhDi19-2(T112A) in Arabidopsis still resulted in salt- and ABA-hypersensitivity phenotypes, like GhDi19-1/-2 transgenic lines. Overexpression of GhDi19-1/-2 and their constitutively activated forms in Atcpk11 background could recover the salt- and ABA-insensitive phenotype of the mutant. Thus, our results demonstrated that Ser phosphorylation (not Thr phosphorylation) is crucial for functionally activating GhDi19-1/-2 in response to salt stress and ABA signaling during early plant development, and GhDi19-1/-2 proteins may be downstream targets of CDPKs in ABA signal pathway.

Transcription Factors and Plants Response to Drought Stress: Current Understanding and Future Directions

Increasing vulnerability of plants to a variety of stresses such as drought, salt and extreme temperatures poses a global threat to sustained growth and productivity of major crops. Of these stresses, drought represents a considerable threat to plant growth and development. In view of this, developing staple food cultivars with improved drought tolerance emerges as the most sustainable solution toward improving crop productivity in a scenario of climate change. In parallel, unraveling the genetic architecture and the targeted identification of molecular networks using modern "OMICS" analyses, that can underpin drought tolerance mechanisms, is urgently required. Importantly, integrated studies intending to elucidate complex mechanisms can bridge the gap existing in our current knowledge about drought stress tolerance in plants. It is now well established that drought tolerance is regulated by several genes, including transcription factors (TFs) that enable plants to withstand unfavorable conditions, and these remain potential genomic candidates for their wide application in crop breeding. These TFs represent the key molecular switches orchestrating the regulation of plant developmental processes in response to a variety of stresses. The current review aims to offer a deeper understanding of TFs engaged in regulating plant's response under drought stress and to devise potential strategies to improve plant tolerance against drought.

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.

Identifying the Location of a Single Protein along the DNA Strand Using Solid-State Nanopores

Solid-state nanopore has been widely studied as an effective tool to detect and analyze small biomolecules, such as DNA, RNA, and proteins, at a single molecule level. In this study, we demonstrate a rapid identification of the location of zinc finger protein (ZFP), which is bound to a specific locus along the length of a double-stranded DNA (dsDNA) to a single protein resolution using a low noise solid-state nanopore. When ZFP labeled DNAs were driven through a nanopore by an externally applied electric field, characteristic ionic current signals arising from the passage of the DNA/ZFP complex and bare DNA were detected, which enabled us to identify the locations of ZFP binding site. We examined two DNAs with ZFP binding sites at different positions and found that the location of the additional current drop derived from the DNA/ZFP complex is well-matched with a theoretical one along the length of the DNA molecule. These results suggest that the protein binding site on DNA can be mapped or that genetic information can be read at a single molecule level using solid-state nanopores.

Arabidopsis drought-induced protein Di19-3 participates in plant response to drought and high salinity stresses

Di19 (drought-induced protein19) family is a novel type of Cys2/His2 zinc-finger proteins. In this study, Arabidopsis Di19-3 was functionally characterized. The experimental results revealed that AtDi19-3 is a transcriptional activator, and could bind to the TACA(A/G)T sequence. AtDi19-3 expression in plants was remarkably induced by NaCl, mannitol and abscisic acid (ABA). T-DNA insertion mutation of AtDi19-3 results in an increase in plant tolerance to drought and high salinity stresses and ABA, whereas overexpression of AtDi19-3 leads to a drought-, salt- and ABA-sensitive phenotype of the transgenic plants. In the presence of NaCl, mannitol or ABA, rates of seed germination and cotyledon greening in Atdi19-3 mutant were higher, but in AtDi19-3 overexpression transgenic plants were lower than those in wild type. Roots of Atdi19-3 mutant seedlings were longer, but those of AtDi19-3 overexpression transgenic seedlings were shorter than those of wild type. Chlorophyll and proline contents in Atdi19-3 mutant were higher, but in AtDi19-3 overexpression seedlings were lower than those in wild type. Atdi19-3 mutant showed greater drought-tolerance, whereas AtDi19-3 overexpression transgenic plants exhibited more drought-sensitivity than wild type. Furthermore, expression of the genes related to ABA signaling pathway was altered in Atdi19-3 mutant and AtDi19-3 transgenic plants. These data suggest that AtDi19-3 may participate in plant response to drought and salt stresses in an ABA-dependent manner.

A novel rice C2H2-type zinc finger protein, ZFP36, is a key player involved in abscisic acid-induced antioxidant defence and oxidative stress tolerance in rice

C2H2-type zinc finger proteins (ZFPs) have been shown to play important roles in the responses of plants to oxidative and abiotic stresses, and different members of this family might have different roles during stresses. Here a novel abscisic acid (ABA)- and hydrogen peroxide (H₂O₂)-responsive C2H2-type ZFP gene, ZFP36, is identified in rice. The analyses of ZFP36-overexpressing and silenced transgenic rice plants showed that ZFP36 is involved in ABA-induced up-regulation of the expression and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). Overexpression of ZFP36 in rice plants was found to elevate the activities of antioxidant enzymes and to enhance the tolerance of rice plants to water stress and oxidative stress. In contrast, an RNA interference (RNAi) mutant of ZFP36 had lower activities of antioxidant enzymes and was more sensitive to water stress and oxidative stress. ABA-induced H₂O₂ production and ABA-activated mitogen-activated protein kinases (MAPKs) were shown to regulate the expression of ZFP36 in ABA signalling. On the other hand, ZFP36 also regulated the expression of NADPH oxidase genes, the production of H₂O₂, and the expression of OsMPK genes in ABA signalling. These results indicate that ZFP36 is required for ABA-induced antioxidant defence, for the tolerance of rice plants to water stress and oxidative stress, and for the regulation of the cross-talk between NADPH oxidase, H₂O₂, and MAPK in ABA signalling.

A soybean C2H2-type zinc finger gene GmZF1 enhanced cold tolerance in transgenic Arabidopsis

Zinc finger proteins were involved in response to different environmental stresses in plant species. A typical Cys2/His2-type (C2H2-type) zinc finger gene GmZF1 from soybean was isolated and was composed of 172 amino acids containing two conserved C2H2-type zinc finger domains. Phylogenetic analysis showed that GmZF1 was clustered on the same branch with six C2H2-type ZFPs from dicotyledonous plants excepting for GsZFP1, and distinguished those from monocotyledon species. The GmZF1 protein was localized at the nucleus, and has specific binding activity with EP1S core sequence, and nucleotide mutation in the core sequence of EPSPS promoter changed the binding ability between GmZF1 protein and core DNA element, implying that two amino acid residues, G and C boxed in core sequence TGACAGTGTCA possibly play positive regulation role in recognizing DNA-binding sites in GmZF1 proteins. High accumulation of GmZF1 mRNA induced by exogenous ABA suggested that GmZF1 was involved in an ABA-dependent signal transduction pathway. Over-expression of GmZF1 significantly improved the contents of proline and soluble sugar and decreased the MDA contents in the transgenic lines exposed to cold stress, indicating that transgenic Arabidopsis carrying GmZF1 gene have adaptive mechanisms to cold stress. Over-expression of GmZF1 also increased the expression of cold-regulated cor6.6 gene by probably recognizing protein-DNA binding sites, suggesting that GmZF1 from soybean could enhance the tolerance of Arabidopsis to cold stress by regulating expression of cold-regulation gene in the transgenic Arabidopsis.

The rice gene OsZFP6 functions in multiple stress tolerance responses in yeast and Arabidopsis

The role of zinc finger proteins in organismal stress conditions has been widely reported. However, little is known concerning the function of CCHC-type zinc finger proteins in rice. In this study, OsZFP6, a rice CCHC-type zinc finger protein 6 gene, was cloned from rice using RT-PCR. The OsZFP6 protein contains 305 amino acids and a conserved zinc finger domain and is localised to the nucleus. Southern blot analysis revealed that a single copy was encoded in the rice genome. OsZFP6 expression was increased by abiotic stress, including salt (NaCl), alkali (NaHCO3) and H2O2 treatment. When OsZFP6 was transformed into yeast, the transgenic yeast showed significantly increased resistance to NaHCO3 compared to the control. Moreover, Arabidopsis transgenic plants overexpressing OsZFP6 were more tolerant to both NaHCO3 and H2O2 treatments. Overall, we uncovered a role for OsZFP6 in abiotic stress responses and identified OsZFP6 as a putatively useful gene for developing crops with increased alkali and H2O2 tolerance.

Arabidopsis Di19 functions as a transcription factor and modulates PR1, PR2, and PR5 expression in response to drought stress

The Arabidopsis Di19 (Drought-induced) gene family encodes seven Cys2/His2-type zinc-finger proteins, most with unknown functions. Here, we report that Di19 functioned as a transcriptional regulator and was involved in Arabidopsis responses to drought stress through up-regulation of pathogenesis-related PR1, PR2, and PR5 gene expressions. The Di19 T-DNA insertion mutant di19 was much more sensitive to drought stress, whereas the Di19-overexpressing lines were much more tolerant to drought stress compared with wild-type plants. Di19 exhibited transactivation activity in our yeast assay, and its transactivation activity was further confirmed in vivo. DNA-binding analysis revealed that Di19 could bind to the TACA(A/G)T element and chromatin immunoprecipitation (ChIP) assays demonstrated that Di19 could bind to the TACA(A/G)T element within the PR1, PR2, and PR5 promoters. qRT-PCR results showed that Di19 promoted the expressions of PR1, PR2, and PR5, and these heightened expressions were enhanced by CPK11, which interacted with Di19 in the nucleus. Similarly to the Di19-overexpressing line, PR1-, PR2-, and PR5-overexpressing lines also showed the drought-tolerant phenotype. The pre-treatment with salicylic acid analogs INA can enhance plants' drought tolerance. Taken together, these data demonstrate that Di19, a new type of transcription factor, directly up-regulates the expressions of PR1, PR2, and PR5 in response to drought stress, and its transactivation activity is enhanced by CPK11.

Promoter of CaZF, a chickpea gene that positively regulates growth and stress tolerance, is activated by an AP2-family transcription factor CAP2

Plants respond to different forms of stresses by inducing transcription of a common and distinct set of genes by concerted actions of a cascade of transcription regulators. We previously reported that a gene, CaZF encoding a C2H2-zinc finger family protein from chickpea (Cicer arietinum) imparted high salinity tolerance when expressed in tobacco plants. We report here that in addition to promoting tolerance against dehydration, salinity and high temperature, the CaZF overexpressing plants exhibited similar phenotype of growth and development like the plants overexpressing CAP2, encoding an AP2-family transcription factor from chickpea. To investigate any relationship between these two genes, we performed gene expression analysis in the overexpressing plants, promoter-reporter analysis and chromatin immunoprecipitation. A number of transcripts that exhibited enhanced accumulation upon expression of CAP2 or CaZF in tobacco plants were found common. Transient expression of CAP2 in chickpea leaves resulted in increased accumulation of CaZF transcript. Gel mobility shift and transient promoter-reporter assays suggested that CAP2 activates CaZF promoter by interacting with C-repeat elements (CRTs) in CaZF promoter. Chromatin immunoprecipitation (ChIP) assay demonstrated an in vivo interaction of CAP2 protein with CaZF promoter.

The heterologous expression in Arabidopsis of a chrysanthemum Cys2/His2 zinc finger protein gene confers salinity and drought tolerance

Zinc finger proteins (ZFPs) play an important role in plant growth and development. Here, we describe the isolation of CgZFP1, a Cys2/His2 (C(2)H(2)) ZFP gene, using RACE PCR from chrysanthemum, and the investigation of its function with ectopic expression in Arabidopsis. CgZFP1 contains two conserved C(2)H(2) regions, a nuclear localization domain (B box), a Leu-rich domain (L box) and a conserved DLN sequence (DLN box) close to its C-terminus. Its expression in the chrysanthemum leaf was strongly induced by salinity or drought, but not by ABA. Subcellular localization assay indicated that CgZFP1 protein is localized in nucleus in vivo. Yeast-one hybrid assay showed that CgZFP1 possesses transcriptional activation ability, heterologous expression of CgZFP1 conferred tolerance of transgenic Arabidopsis plants to both salinity and drought stresses. Under salinity stress, genes involved in osmotic adjustment, ROS scavenging, and ion homeostasis: Atlea3, AtP5CS2, AtProT1, and AtMnSOD, AtPOD, AtAPX1, and AtSOS1, AtSOS2, AtSOS3, AtNHX1 were enhanced in CgZFP1 transgenic Arabidopsis plants. Moreover, genes involved in the osmotic adjustment and oxidative stress responses: Atlea3, AtP5CS2, AtProT1, the aquaporin AtPIP2A, and AtMnSOD, AtPOD, AtAPX1 were induced in CgZFP1 transgenic Arabidopsis under drought stress. These results indicate CgZFP1 is an important regulator involved in the salt and drought stress response in plants.

Identification and expression of C2H2 transcription factor genes in Carica papaya under abiotic and biotic stresses

C2H2 proteins belong to a group of transcription factors (TFs) existing as a superfamily that plays important roles in defense responses and various other physiological processes in plants. The present study aimed to screen for and identify C2H2 proteins associated with defense responses to abiotic and biotic stresses in Carica papaya L. Data were collected for 47,483 papaya-expressed sequence tags (ESTs). The full-length cDNA nucleotide sequences of 87 C2H2 proteins were predicated by BioEdit. All 91 C2H2 proteins were aligned, and a phylogenetic tree was constructed using DNAman. The expression levels of 42 C2H2 were analyzed under conditions of salt stress by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Methyl jasmonate treatment rapidly upregulated ZF(23.4) and ZF(30,912.1) by 18.6- and 21.7-fold, respectively. ZF(1.3), ZF(138.44), ZF(94.49), ZF(29.160), and ZF(20.206) were found to be downregulated after low temperature treatment at very significant levels (p < 0.01). ZF(23.4), ZF(161.1), and ZF(30,912.1) were upregulated while ZF1.3, ZF(158.1), ZF(249.5), ZF(138.44), ZF(94.49), ZF(29.160), and ZF(20.206) were significantly downregulated by Spermine treatment. ZF(23.4) was upregulated while ZF(1.3), ZF(249.5), ZF(94.94), ZF(29.160), ZF(138.44), and ZF(20.206) were significantly repressed after SA treatment. ZF(23.4) and ZF(30,912.1) were significantly upregulated after sap inoculation with papaya ringspot virus pathogen. ZF(30,912.1) was subcellularly localized in the nucleus by a transgenic fusion of pBS-ZF(30,912.1)-GFP into the protoplast of papaya. The results of the present study showed that ZF(30,912.1) could be an important TF that mediates responses to abiotic and biotic stresses in papaya.

Involvement of plant C(2)H(2)-type zinc finger transcription factors in stress responses

Abiotic and biotic stresses frequently impose constraints on plant distribution and affect agricultural productivity. Various aspects of the multiplicity and the complexity of stress responsive gene networks have been previously studied. Many of individual transcription factors in plants and their family classes that regulate the expression of several genes in responses to environmental stresses have been identified. One such class of transcription regulators is the C(2)H(2) class of zinc finger proteins. Numerous members of the C(2)H(2)-type zinc finger family have been shown to play diverse roles in the plant stress response and the hormone signal transduction. Transcription profiling analyses have demonstrated that the transcript level of many C(2)H(2)-type zinc finger proteins is elevated under different abiotic stress conditions such as low temperature, salt, drought, osmotic stress and oxidative stress. Some C(2)H(2)-type proteins are additionally involved in the biotic stress signaling pathway. Moreover, it has been reported that overexpression of some C(2)H(2)-type zinc finger protein genes resulted in both the activation of some stress-related genes and enhanced tolerance to various stresses. Current genetic studies have focused on possible interactions between different zinc finger transcription factors during stresses to regulate transcription. This review highlights the role of the C(2)H(2) class of the zinc finger proteins in regulating abiotic and biotic stress tolerance in the plants.

Identification and characterization of a salt stress-inducible zinc finger protein from Festuca arundinacea

Background

Increased biotic and abiotic plant stresses due to climate change together with an expected global human population of over 9 billion by 2050 intensifies the demand for agricultural production on marginal lands. Soil salinity is one of the major abiotic stresses responsible for reduced crop productivity worldwide and the salinization of arable land has dramatically increased over the last few decades. Consequently, as land becomes less amenable for conventional agriculture, plants grown on marginal soils will be exposed to higher levels of soil salinity. Forage grasses are a critical component of feed used in livestock production worldwide, with many of these same species of grasses being utilized for lawns, erosion prevention, and recreation. Consequently, it is important to develop a better understanding of salt tolerance in forage and related grass species.

Findings

A gene encoding a ZnF protein was identified during the analysis of a salt-stress suppression subtractive hybridization (SSH) expression library from the forage grass species Festuca arundinacea. The expression pattern of FaZnF was compared to that of the well characterized gene for delta 1-pyrroline-5-carboxylate synthetase (P5CS), a key enzyme in proline biosynthesis, which was also identified in the salt-stress SSH library. The FaZnF and P5CS genes were both up-regulated in response to salt and drought stresses suggesting a role in dehydration stress. FaZnF was also up-regulated in response to heat and wounding, suggesting that it might have a more general function in multiple abiotic stress responses. Additionally, potential downstream targets of FaZnF (a MAPK [Mitogen-Activated Protein Kinase], GST [Glutathione-S-Transferase] and lipoxygenase L2) were found to be up-regulated in calli overexpressing FaZnF when compared to control cell lines.

Conclusions

This work provides evidence that FaZnF is an AN1/A20 zinc finger protein that is involved in the regulation of at least two pathways initiated by the salt stress response, thus furthering our understanding of the mechanisms of cellular action during a stress that is applicable to commercial crops worldwide.

A novel zinc-finger-like gene from Tamarix hispida is involved in salt and osmotic tolerance

In the present study, a zinc-finger-like cDNA (ThZFL) was cloned from the Tamarix hispida. Northern blot analysis showed that the expression of ThZFL can be induced by salt, osmotic stress and ABA treatment. Overexpression of the ThZFL confers salt and osmotic stress tolerance in both yeast Saccharomyces cerevisiae and tobacco. Furthermore, MDA levels in ThZFL transformed tobacco were significantly decreased compared with control plants under salt and osmotic stress, suggesting ThZFL may confer stress tolerance by decreasing membrane lipid peroxidation. Subcellular localization analysis showed the ThZFL protein is localized in the cell wall. Our results indicated the ThZFL gene is an excellent candidate for genetic engineering to improve salt and osmotic tolerance in agricultural plants.

Arabidopsis MAP kinase phosphatase 1 is phosphorylated and activated by its substrate AtMPK6

Arabidopsis MAP kinase phosphatase 1 (AtMKP1) is a member of the mitogen-activated protein kinase (MPK) phosphatase family, which negatively regulates AtMPKs. We have previously shown that AtMKP1 is regulated by calmodulin (CaM). Here, we examined the phosphorylation of AtMKP1 by its substrate AtMPK6. Intriguingly, AtMKP1 was phosphorylated by AtMPK6, one of AtMKP1 substrates. Four phosphorylation sites were identified by phosphoamino acid analysis, TiO(2) chromatography and mass spectrometric analysis. Site-directed mutation of these residues in AtMKP1 abolished the phosphorylation by AtMPK6. In addition, AtMKP1 interacted with AtMPK6 as demonstrated by the yeast two-hybrid system. Finally, the phosphatase activity of AtMKP1 increased approximately twofold following phosphorylation by AtMPK6. By in-gel kinase assays, we showed that AtMKP1 could be rapidly phosphorylated by AtMPK6 in plants. Our results suggest that the catalytic activity of AtMKP1 in plants can be regulated not only by Ca(2+)/CaM, but also by its physiological substrate, AtMPK6.

Phylogenetic study of plant Q-type C2H2 zinc finger proteins and expression analysis of poplar genes in response to osmotic, cold and mechanical stresses

Plant Q-type C2H2 zinc finger transcription factors play an important role in plant tolerance to various environmental stresses such as drought, cold, osmotic stress, wounding and mechanical loading. To carry out an improved analysis of the specific role of each member of this subfamily in response to mechanical loading in poplar, we identified 16 two-fingered Q-type C2H2-predicted proteins from the poplar Phytozome database and compared their phylogenetic relationships with 152 two-fingered Q-type C2H2 protein sequences belonging to more than 50 species isolated from the NR protein database of NCBI. Phylogenetic analyses of these Q-type C2H2 proteins sequences classified them into two groups G1 and G2, and conserved motif distributions of interest were established. These two groups differed essentially in their signatures at the C-terminus of their two QALGGH DNA-binding domains. Two additional conserved motifs, MALEAL and LVDCHY, were found only in sequences from Group G1 or from Group G2, respectively. Functional significance of these phylogenetic divergences was assessed by studying transcript accumulation of six poplar C2H2 Q-type genes in responses to abiotic stresses; but no group specificity was found in any organ. Further expression analyses focused on PtaZFP1 and PtaZFP2, the two genes strongly induced by mechanical loading in poplars. The results revealed that these two genes were regulated by several signalling molecules including hydrogen peroxide and the phytohormone jasmonate.

The putative Arabidopsis zinc transporter ZTP29 is involved in the response to salt stress

Salt stress leads to a stress response, called the unfolded protein response (UPR), in the endoplasmic reticulum (ER). UPR is also induced in a wide range of organisms by zinc deficiency. However, it is not clear whether regulation of zinc levels is involved in the initiation of the UPR in plant response to salt stress. In this study, a putative zinc transporter, ZTP29, was identified in Arabidopsis thaliana. ZTP29 localizes to the ER membrane and is expressed primarily in hypocotyl and cotyledon tissues, but its expression can be induced in root tissue by salt stress. T-DNA insertion into the ZTP29 gene led to NaCl hypersensitivity in seed germination and seedling growth, leaf etiolation, and widening of cells in the root elongation zone. In addition, in ztp29 mutant plants, salt stress-induced upregulation of the UPR pathway genes BiP2 and bZIP60 was inhibited. Furthermore, under conditions of salt stress, upregulation of BiP2 and bZIP60 was inhibited by treatment with high concentrations of zinc in both control and ztp29 plants. However, zinc chelation restored salt stress-induced BiP2 and bZIP60 upregulation in ztp29 mutant plants. These experimental results suggest that ZTP29 is involved in the response to salt stress, perhaps through regulation of zinc levels required to induce the UPR pathway.

Functional analysis of a novel Cys2/His2-type zinc finger protein involved in salt tolerance in rice

The Cys2/His2-type zinc finger proteins have been implicated in different cellular processes involved in plant development and stress responses. Through microarray analysis, a salt-responsive zinc finger protein gene ZFP179 was identified and subsequently cloned from rice seedlings. ZFP179 encodes a 17.95 kDa protein with two C2H2-type zinc finger motifs having transcriptional activation activity. The real-time RT-PCR analysis showed that ZFP179 was highly expressed in immature spikes, and markedly induced in the seedlings by NaCl, PEG 6000, and ABA treatments. Overexpression of ZFP179 in rice increased salt tolerance and the transgenic seedlings showed hypersensitivity to exogenous ABA. The increased levels of free proline and soluble sugars were observed in transgenic plants compared to wild-type plants under salt stress. The ZFP179 transgenic rice exhibited significantly increased tolerance to oxidative stress, the reactive oxygen species (ROS)-scavenging ability, and expression levels of a number of stress-related genes, including OsDREB2A, OsP5CS OsProT, and OsLea3 under salt stress. Our studies suggest that ZFP179 plays a crucial role in the plant response to salt stress, and is useful in developing transgenic crops with enhanced tolerance to salt stress.

Identification of salt-induced genes from Salicornia brachiata, an extreme halophyte through expressed sequence tags analysis

Salinity severely affects plant growth and development causing crop loss worldwide. We have isolated a large number of salt-induced genes as well as unknown and hypothetical genes from Salicornia brachiata Roxb. (Amaranthaceae). This is the first description of identification of genes in response to salinity stress in this extreme halophyte plant. Salicornia accumulates salt in its pith and survives even at 2 M NaCl under field conditions. For isolating salt responsive genes, cDNA subtractive hybridization was performed between control and 500 mM NaCl treated plants. Out of the 1200 recombinant clones, 930 sequences were submitted to the NCBI database (GenBank accession: EB484528 to EB485289 and EC906125 to EC906292). 789 ESTs showed matching with different genes in NCBI database. 4.8% ESTs belonged to stress-tolerant gene category and approximately 29% ESTs showed no homology with known functional gene sequences, thus classified as unknown or hypothetical. The detection of a large number of ESTs with unknown putative function in this species makes it an interesting contribution. The 90 unknown and hypothetical genes were selected to study their differential regulation by reverse Northern analysis for identifying their role in salinity tolerance. Interestingly, both up and down regulation at 500 mM NaCl were observed (21 and 10 genes, respectively). Northern analysis of two important salt tolerant genes, ASR1 (Abscisic acid stress ripening gene) and plasma membrane H+ATPase, showed the basal level of transcripts in control condition and an increase with NaCl treatment. ASR1 gene is made full length using 5' RACE and its potential role in imparting salt tolerance is being studied.

Increased tolerance of rice to cold, drought and oxidative stresses mediated by the overexpression of a gene that encodes the zinc finger protein ZFP245

ZFP245 is a cold- and drought-responsive gene that encodes a zinc finger protein in rice. The ZFP245 protein localizes in the nucleus and exhibits trans-activation activity. Transgenic rice plants overexpressing ZFP245 were generated and found to display high tolerance to cold and drought stresses. The transgenic plants did not exhibit growth retardation, but showed growth sensitivity against exogenous abscisic acid, increased free proline levels and elevated expression of rice pyrroline-5-carboxylatesynthetase and proline transporter genes under stress conditions. Overproduction of ZFP245 enhanced the activities of reactive oxygen species-scavenging enzymes under stress conditions and increased the tolerance of rice seedlings to oxidative stress. Our data suggest that ZFP245 may contribute to the tolerance of rice plants to cold and drought stresses by regulating proline levels and reactive oxygen species-scavenging activities, and therefore may be useful for developing transgenic crops with enhanced tolerance to abiotic stress.

A previously unknown zinc finger protein, DST, regulates drought and salt tolerance in rice via stomatal aperture control

Abiotic stresses, such as drought and salinity, lead to crop growth damage and a decrease in crop yields. Stomata control CO(2) uptake and optimize water use efficiency, thereby playing crucial roles in abiotic stress tolerance. Hydrogen peroxide (H(2)O(2)) is an important signal molecule that induces stomatal closure. However, the molecular pathway that regulates the H(2)O(2) level in guard cells remains largely unknown. Here, we clone and characterize DST (drought and salt tolerance)-a previously unknown zinc finger transcription factor that negatively regulates stomatal closure by direct modulation of genes related to H(2)O(2) homeostasis-and identify a novel pathway for the signal transduction of DST-mediated H(2)O(2)-induced stomatal closure. Loss of DST function increases stomatal closure and reduces stomatal density, consequently resulting in enhanced drought and salt tolerance in rice. These findings provide an interesting insight into the mechanism of stomata-regulated abiotic stress tolerance, and an important genetic engineering approach for improving abiotic stress tolerance in crops.

Screening of genes induced by salt stress from Alfalfa

An alfalfa cDNA library induced by salt stress was constructed by suppression subtraction hybridization (SSH) technology. Total RNA from 10-day-old seedlings was used as a "driver," and total RNA from seedlings induced by salt was used as a "tester". One hundred and nineteen clones identified as positive clones by reverse Northern dot-blotting resulted in 82 uni-ESTs comprised of 16 contigs and 66 singletons. Blast analysis of deduced protein sequences revealed that 51 ESTs had identity similar to proteins with known function, while 24 could not be annotated at all. Most of the annotated sequences were homologous to genes involved in abiotic or biotic stress in plants. Among these proteins, beta-amylase, fructose-1,6-bisphosphate, aldolase, and sucrose synthase are related to osmolyte synthesis; a CCCH-type zinc finger protein, DNA binding protein, His-Asp phosphotransfer protein, and the RelA/SpoT protein partake in transcription regulation and signal transduction; and ribulose-l,5-bisphosphate carboxylase/oxygenase, chlorophyll a/b binding proteins, and an early light-inducible proteins are related to photosynthesis. In addition, several ESTs, similar to genes from other plant species, closely involved in salt stress were isolated from alfalfa, such as an aquaporin protein, a late embryogenesis-abundant protein, and glutathione peroxidase.

Learning from evolution: Thellungiella generates new knowledge on essential and critical components of abiotic stress tolerance in plants

Thellungiella salsuginea (halophila) is a close relative of Arabidopsis thaliana but, unlike A. thaliana, it grows well in extreme conditions of cold, salt, and drought as well as nitrogen limitation. Over the last decade, many laboratories have started to use Thellungiella to investigate the physiological, metabolic, and molecular mechanisms of abiotic stress tolerance in plants, and new knowledge has been gained in particular with respect to ion transport and gene expression. The advantage of Thellungiella over other extremophile model plants is that it can be directly compared with Arabidopsis, and therefore generate information on both essential and critical components of stress tolerance. Thellungiella research is supported by a growing body of technical resources comprising physiological and molecular protocols, ecotype collections, expressed sequence tags, cDNA-libraries, microarrays, and a pending genome sequence. This review summarizes the current state of knowledge on Thellungiella and re-evaluates its usefulness as a model for research into plant stress tolerance.