A novel stress-associated protein 'AtSAP10' from Arabidopsis thaliana confers tolerance to nickel, manganese, zinc, and high temperature stress

Genome-wide identification and evolution of the SAP gene family in sunflower (Helianthus annuus L.) and expression analysis under salt and drought stress

Stress-associated proteins (SAPs) are known to play an important role in plant responses to abiotic stresses. This study systematically identified members of the sunflower SAP gene family using sunflower genome data. The genes of the sunflower SAP gene family were analyzed using bioinformatic methods, and gene expression was assessed through fluorescence quantification (qRT-PCR) under salt and drought stress. A comprehensive analysis was also performed on the number, structure, collinearity, and phylogeny of seven Compositae species and eight other plant SAP gene families. The sunflower genome was found to have 27 SAP genes, distributed across 14 chromosomes. The evolutionary analysis revealed that the SAP family genes could be divided into three subgroups. Notably, the annuus variety exhibited amplification of the SAP gene for Group 3. Among the Compositae species, C. morifolium demonstrated the highest number of collinearity gene pairs and the closest distance on the phylogenetic tree, suggesting relative conservation in the evolutionary process. An analysis of gene structure revealed that Group 1 exhibited the most complex gene structure, while the majority of HaSAP genes in Group 2 and Group 3 lacked introns. The promoter analysis revealed the presence of cis-acting elements related to ABA, indicating their involvement in stress responses. The expression analysis indicated the potential involvement of 10 genes (HaSAP1, HaSAP3, HaSAP8, HaSAP10, HaSAP15, HaSAP16, HaSAP21, HaSAP22, HaSAP23, and HaSAP26) in sunflower salt tolerance. The expression of these 10 genes were then examined under salt and drought stress using qRT-PCR, and the tissue-specific expression patterns of these 10 genes were also analyzed. HaSAP1, HaSAP21, and HaSAP23 exhibited consistent expression patterns under both salt and drought stress, indicating these genes play a role in both salt tolerance and drought resistance in sunflower. The findings of this study highlight the significant contribution of the SAP gene family to salt tolerance and drought resistance in sunflower.

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 μg g^-1, while the limit for soil is between 75 and 150 μg g^-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

AoSAP8-P encoding A20 and/or AN1 type zinc finger protein in asparagus officinalis L. Improving stress tolerance in transgenic Nicotiana sylvestris

The full length CDS of an A20 and AN1 type zinc finger gene (named AoSAP8-P), located nearby the male specific Y chromosome (MSY) region of Asparagus officinalis (garden asparagus) was amplified by RT-PCR from purple passion. This gene, predicted as the stress associated protein (SAPs) gene families, encodes 172 amino acids with multiple cis elements including light, stress response box, MYB and ERF binding sites on its promoter. To analyze its function, the gene expression of different organs in different asparagus gender were analyzed and the overexpressed transgenic Nicotiana sylvestris lines were generated. The results showed the gene was highly expressed in both flower and root of male garden asparagus; the germination rate of seeds of the T2 transgenic lines (T2-5-4 and T2-7-1) under the stress conditions of 125 mM NaCl and 150 mM mannitol were significantly higher than the wild type (WT) respectively. When the potted T2-5-4, T2-7-1 lines and WT were subjected to drought stress for 24 days and the leaf discs immerged into 20 % PEG6000 and 300 mM NaCl solution for 48 h respectively, the T2-5-4 and T2-7-1 with AoSAP8-P expression showed stronger drought, salt and osmotic stress tolerance. When compared, the effects of AoSAP8-P overexpression on productive development showed that the flowering time of transgenic lines, were ∼ 9 day earlier with larger but fewer pollens than its WT counterparts. However, there were no significant differences in anthers, stigmas and pollen viability between the transgenic lines and WT. Our results suggested that, the AoSAP8-P gene plays a role in improving the stress resistance and shortening seeds generation time for perianal survival during the growth and development of garden asparagus.

Identification of multiple novel genetic mechanisms that regulate chilling tolerance in Arabidopsis

INTRODUCTION

Cold stress adversely affects the growth and development of plants and limits the geographical distribution of many plant species. Accumulation of spontaneous mutations shapes the adaptation of plant species to diverse climatic conditions.

METHODS

The genome-wide association study of the phenotypic variation gathered by a newly designed phenomic platform with the over six millions single nucleotide polymorphic (SNP) loci distributed across the genomes of 417 Arabidopsis natural variants collected from various geographical regions revealed 33 candidate cold responsive genes.

RESULTS

Investigation of at least two independent insertion mutants for 29 genes identified 16 chilling tolerance genes governing diverse genetic mechanisms. Five of these genes encode novel leucine-rich repeat domain-containing proteins including three nucleotide-binding site-leucine-rich repeat (NBS-LRR) proteins. Among the 16 identified chilling tolerance genes, ADS2 and ACD6 are the only two chilling tolerance genes identified earlier.

DISCUSSION

The 12.5% overlap between the genes identified in this genome-wide association study (GWAS) of natural variants with those discovered previously through forward and reverse genetic approaches suggests that chilling tolerance is a complex physiological process governed by a large number of genetic mechanisms.

The intertwining of Zn-finger motifs and abiotic stress tolerance in plants: Current status and future prospects

Environmental stresses such as drought, high salinity, and low temperature can adversely modulate the field crop's ability by altering the morphological, physiological, and biochemical processes of the plants. It is estimated that about 50% + of the productivity of several crops is limited due to various types of abiotic stresses either presence alone or in combination (s). However, there are two ways plants can survive against these abiotic stresses; a) through management practices and b) through adaptive mechanisms to tolerate plants. These adaptive mechanisms of tolerant plants are mostly linked to their signalling transduction pathway, triggering the action of plant transcription factors and controlling the expression of various stress-regulated genes. In recent times, several studies found that Zn-finger motifs have a significant function during abiotic stress response in plants. In the first report, a wide range of Zn-binding motifs has been recognized and termed Zn-fingers. Since the zinc finger motifs regulate the function of stress-responsive genes. The Zn-finger was first reported as a repeated Zn-binding motif, comprising conserved cysteine (Cys) and histidine (His) ligands, in Xenopus laevis oocytes as a transcription factor (TF) IIIA (or TFIIIA). In the proteins where Zn²⁺ is mainly attached to amino acid residues and thus espousing a tetrahedral coordination geometry. The physical nature of Zn-proteins, defining the attraction of Zn-proteins for Zn²⁺, is crucial for having an in-depth knowledge of how a Zn²⁺ facilitates their characteristic function and how proteins control its mobility (intra and intercellular) as well as cellular availability. The current review summarized the concept, importance and mechanisms of Zn-finger motifs during abiotic stress response in plants.

Pepper stress-associated protein 14 is a substrate of CaSnRK2.6 that positively modulates abscisic acid-dependent osmotic stress responses

The phytohormone abscisic acid (ABA) plays a prominent role in various abiotic stress responses of plants. In the ABA-dependent osmotic stress response, SnRK2.6, one of the subclass III SnRK2 kinases, has been identified as playing a key role by phosphorylating and activating downstream genes. Although several modulatory proteins have been reported to be phosphorylated by SnRK2.6, the identities of the full spectrum of downstream targets have yet to be sufficiently established. In this study, we identified CaSAP14, a stress-associated protein in pepper (Capsicum annuum), as a downstream target of CaSnRK2.6. We elucidated the physical interaction between SnRK2.6 and CaSAP14, both in vitro and in vivo, and accordingly identified a C-terminal C2H2-type zinc finger domain of CaSAP14 as being important for their interaction. CaSAP14-silenced pepper plants showed dehydration- and high salt-sensitive phenotypes, whereas overexpression of CaSAP14 in Arabidopsis conferred tolerance to dehydration, high salinity, and mannitol treatment, with plants showing ABA-hypersensitive phenotypes. Furthermore, an in-gel kinase assay revealed that CaSnRK2.6 phosphorylates CaSAP14 in response to exogenous ABA, dehydration, and high-salinity stress. Collectively, these findings suggest that CaSAP14 is a direct substrate of CaSnRK2.6 and positively modulates dehydration- and high salinity-induced osmotic stress responses.

OsSAP6 Positively Regulates Soda Saline-Alkaline Stress Tolerance in Rice

BACKGROUND

Soil salinization is a worldwide environmental problem, especially in the arid and semiarid regions of northeastern China, which are heavily affected by soda saline-alkaline stress. At present, there is an urgent need to improve the soda saline-alkaline stress tolerance of rice.

RESULTS

Stress-associated proteins are involved in regulating the abiotic stresses in plants. There are 18 members of the rice stress-associated protein (OsSAP) gene family. In this study, the expression levels of OsSAP6 in leaves and roots were upregulated with increasing NaHCO₃ stress duration. OsSAP6 was located in nucleus and cytoplasm. The bud length and total root length of OsSAP6 overexpression rice were significantly longer than those of Lj11 (Oryza sativa longjing11) during germination stage, and the survival rates, plant height and malondialdehyde content at the seedling stage showed tolerance growth of saline-alkaline stress. The expression of OsCu/Zn-SOD, OsAPX2, and OsCAT1 in transgenic lines was increased significantly under SAE (soda saline-alkali soil eluent) stress. OsSAP6 interacts with OsPK5 according to yeast two-hybrid screening and luciferase complementation experiments. The expression of OsPK5 increased under NaHCO₃ and H₂O₂ stress, and the overexpression of OsPK5 in rice improved soda saline-alkaline tolerance.

CONCLUSION

Overexpression of OsSAP6 in rice significantly enhanced saline-alkaline tolerance compared with the wild type. It is speculated that OsSAP6 responds to soda salinity stress and interacts with OsPK5 to positively regulate soda saline-alkaline tolerance through ROS homeostasis. This study revealed the features of OsSAP6 involved in response to soda saline-alkaline stress and the interaction with OsPK5, which provided resources for breeding aimed at improving the soda saline-alkaline stress tolerance of rice.

Identification and Analysis of Stress-Associated Proteins (SAPs) Protein Family and Drought Tolerance of ZmSAP8 in Transgenic Arabidopsis

Stress-associated proteins (SAPs), a class of A20/AN1 zinc finger proteins, play vital roles in plant stress response. However, investigation of SAPs in maize has been very limited. Herein, to better trace the evolutionary history of SAPs in maize and plants, 415 SAPs were identified in 33 plant species and four species of other kingdoms. Moreover, gene duplication mode exploration showed whole genome duplication contributed largely to SAP gene expansion in angiosperms. Phylogeny reconstruction was performed with all identified SAPs by the maximum likelihood (ML) method and the SAPs were divided into five clades. SAPs within the same clades showed conserved domain composition. Focusing on maize, nine ZmSAPs were identified. Further promoter cis-elements and stress-induced expression pattern analysis of ZmSAPs indicated that ZmSAP8 was a promising candidate in response to drought stress, which was the only AN1-AN1-C2H2-C2H2 type SAP in maize and belonged to clade I. Additionally, ZmSAP8 was located in the nucleus and had no transactivation activity in yeast. Overexpressing ZmSAP8 enhanced the tolerance to drought stress in Arabidopsis thaliana, with higher seed germination and longer root length. Our results should benefit the further functional characterization of ZmSAPs.

Large-scale comparative transcriptomic analysis of temperature-responsive genes in Arabidopsis thaliana

Comparative transcriptomic analysis provides broad and detailed understandings of transcriptional responses to a wide range of temperatures in different plant tissues, and unique regulatory functions of temperature-mediating transcription factors. Climate change poses a great threat to plant diversity and food security. It is thus of necessity to understand the molecular mechanisms for perceiving and responding to adverse temperature changes, to develop the cultivars that are resilient to these environmental stresses. Making use of publicly available datasets, we gathered and re-analyzed 259 individual transcriptomic profiles from 139 unique experiments of Arabidopsis thaliana's shoot, root, and seedling tissues, subjected to a wide variety of temperature conditions, ranging from freezing, cold, low and high ambient temperatures, to heat shock. Despite the underlying differences in the overall transcriptomic profiles between the plant tissues, we were able to identify distinct sets of genes whose transcription patterns were highly responsive to different types of temperature conditions, some were common among the tissues and some were tissue-specific. Interestingly, we observed that the known temperature-responsive genes such as the heat-shock factor (HSF) family, were up-regulated not only in response to high temperatures, but some of its members were also likely involved in the cold response. By integrating the DNA-binding specificity information of the key temperature transcription factor (TF) HSFA1a, PIF4, and CBFs, we elucidated their distinct DNA-binding patterns to the target genes that showed different transcriptional responses. Taken together, we have comprehensively characterized the transcription patterns of temperature-responsive genes and provided directly testable hypotheses on the regulatory roles of key temperature TFs on the expression dynamics of their target genes.

Genome-Wide Identification of the A20/AN1 Zinc Finger Protein Family Genes in Ipomoea batatas and Its Two Relatives and Function Analysis of IbSAP16 in Salinity Tolerance

Stress-associated protein (SAP) genes—encoding A20/AN1 zinc-finger domain-containing proteins—play pivotal roles in regulating stress responses, growth, and development in plants. They are considered suitable candidates to improve abiotic stress tolerance in plants. However, the SAP gene family in sweetpotato (Ipomoea batatas) and its relatives is yet to be investigated. In this study, 20 SAPs in sweetpotato, and 23 and 26 SAPs in its wild diploid relatives Ipomoea triloba and Ipomoea trifida were identified. The chromosome locations, gene structures, protein physiological properties, conserved domains, and phylogenetic relationships of these SAPs were analyzed systematically. Binding motif analysis of IbSAPs indicated that hormone and stress responsive cis-acting elements were distributed in their promoters. RT-qPCR or RNA-seq data revealed that the expression patterns of IbSAP, ItbSAP, and ItfSAP genes varied in different organs and responded to salinity, drought, or ABA (abscisic acid) treatments differently. Moreover, we found that IbSAP16 driven by the 35 S promoter conferred salinity tolerance in transgenic Arabidopsis. These results provided a genome-wide characterization of SAP genes in sweetpotato and its two relatives and suggested that IbSAP16 is involved in salinity stress responses. Our research laid the groundwork for studying SAP-mediated stress response mechanisms in sweetpotato.

Genome-wide in silico identification and characterization of the stress associated protein (SAP) gene family encoding A20/AN1 zinc-finger proteins in potato (Solanum tuberosum L.)

Stress associated proteins (SAPs) in plants have a key role in providing tolerance to multiple abiotic stresses. SAP gene family in Solanum tuberosum has not been fully studied before. This study identified 17 StSAP genes in S. tuberosum which code for A20/AN1 zinc-finger proteins. All the genes were distributed on ten different chromosomes and six segmental duplication events were identified. The SAPs in S. tuberosum and its orthologs in Arabidopsis thaliana were classified into six groups through the phylogenetic analysis. Introns across StSAP genes were identified in four genes. The promotor study of the StSAP genes showed different hormone and stress-related cis-elements that could potentially have a role in environmental stress response. The expression of StSAP genes in response to heat, mannitol, and salt were analyzed through in silico transcriptomic analysis. This study could potentially help in further understanding the functions of SAP genes in S. tuberosum.

Essential trace metals in plant responses to heat stress

Essential trace metals function as structural components or cofactors in many proteins involved in a wide range of physiological processes in plants. Hence, trace metal deficiency can significantly hamper plant growth and development. On the other hand, excess concentrations of trace metals can also induce phytotoxicity, for example via an enhanced production of reactive oxygen species. Besides their roles in plant growth under favourable environmental conditions, trace metals also contribute to plant responses to biotic and abiotic stresses. Heat is a stress factor that will become more prevalent due to increasing climate change and is known to negatively affect crop yield and quality, posing a severe threat to food security for future generations. Gaining insight into heat stress responses is essential to develop strategies to optimize plant growth and quality under unfavourable temperatures. In this context, trace metals deserve particular attention as they contribute to defence responses and are important determinants of plant nutritional value. Here, we provide an overview of heat-induced effects on plant trace metal homeostasis and the involvement of trace metals and trace metal-dependent enzymes in plant responses to heat stress. Furthermore, avenues for future research on the interactions between heat stress and trace metals are discussed.

Identification and Expression Analysis of Zinc Finger A20/AN1 Stress-Associated Genes SmSAP Responding to Abiotic Stress in Eggplant

Stress-associated proteins (SAP), a class of zinc-finger proteins, have been identified as novel stress regulatory proteins in stress responses. However, SAP genes in eggplant (SmSAP) have been little reported. It has important significance in identifying SAP members, understanding the molecular mechanisms underlying stress responses, and tolerance. We performed a comprehensive study of the A20/AN1 domains, motifs, gene structures, phylogenetic relationships, chromosomal locations, gene replications, collinearity, cis-acting elements, and expression pattern responses to various abiotic stresses. Twenty-one SAP genes were identified in eggplant (SmSAP) and were localized on 10 chromosomes. A phylogenetic analysis revealed that most of the SmSAP proteins showed a high homology with the tomato SAP members, and 21 members were divided into four groups based on the homology of the SAP members in eggplant, tomato, rice, and Arabidopsis. Further analysis revealed that SmSAP proteins contain the characteristic A20/AN1 domains, the A20 domain composed of motif 2 (ILCINNCGFFGSPATMNLCSKCYKDMJLK). Four pairs of tandem duplications were found in eggplant, and 10 SmSAP genes had collinearity with SAP genes from Arabidopsis, potato, or tomato, but only four SmSAP genes were collinear with SAP genes in the three species mentioned above. Moreover, the promoters of SmSAP genes were predicted to contain many cis-acting elements that respond to abiotic stress and hormones. A qRT-PCR analysis of the four selected SmSAP genes exhibited diverse expression levels in response to various environmental stresses. These results provided a comprehensive analysis of the SmSAP genes and lay a solid foundation for improving the understanding of the functional diversification of SAP genes under various environmental stresses in eggplant.

Differential Functions of Pepper Stress-Associated Proteins in Response to Abiotic Stresses

Stress-associated proteins (SAPs), a group of zinc-finger-type proteins, have been identified as novel regulators of plant abiotic and biotic stresses. However, although they have been discovered in different plant species, their precise functional roles remain unclear. Here, we identified 14 SAP subfamily genes in the pepper genome. An investigation of the promoter regions of these genes for cis-regulatory elements associated with abiotic stress responses revealed the presence of multiple stress-related elements. Domain and phylogenetic analyses using the corresponding protein sequences revealed that the CaSAP genes can be classified into six groups (I-VI) and sorted into two broad types. Expression levels of the CaSAP genes were found to be differentially induced by low temperature, the dehydration stress, or exogenous abscisic acid. Group II and IV genes were highly induced by the low temperature and dehydration treatments, respectively. Moreover, subcellular localization analysis indicated that the proteins in these two groups are distributed in the nucleus, cytoplasm, and plasma membrane. Among the pepper plants silenced with the three identified group II CaSAP genes, the CA02g10410-silenced plants showed tolerance to low temperature, whereas the CA03g17080-silenced plants were found to have temperature-sensitive phenotypes. Interestingly, group IV CaSAP-silenced pepper plants showed drought-tolerant phenotypes. These findings contribute to a preliminary characterization of CaSAP genes and provide directions for future research on the biological role of CaSAPs in response to different abiotic stresses.

Ampelopsin Confers Endurance and Rehabilitation Mechanisms in Glycine max cv. Sowonkong under Multiple Abiotic Stresses

The present investigation aims to perceive the effect of exogenous ampelopsin treatment on salinity and heavy metal damaged soybean seedlings (Glycine max L.) in terms of physiochemical and molecular responses. Screening of numerous ampelopsin concentrations (0, 0.1, 1, 5, 10 and 25 μM) on soybean seedling growth indicated that the 1 μM concentration displayed an increase in agronomic traits. The study also determined how ampelopsin application could recover salinity and heavy metal damaged plants. Soybean seedlings were irrigated with water, 1.5% NaCl or 3 mM chosen heavy metals for 12 days. Our results showed that the application of ampelopsin raised survival of the 45-day old salinity and heavy metal stressed soybean plants. The ampelopsin treated plants sustained high chlorophyll, protein, amino acid, fatty acid, salicylic acid, sugar, antioxidant activities and proline contents, and displayed low hydrogen peroxide, lipid metabolism, and abscisic acid contents under unfavorable status. A gene expression survey revealed that ampelopsin application led to the improved expression of GmNAC109, GmFDL19, GmFAD3, GmAPX, GmWRKY12, GmWRKY142, and GmSAP16 genes, and reduced the expression of the GmERF75 gene. This study suggests irrigation with ampelopsin can alleviate plant damage and improve plant yield under stress conditions, especially those including salinity and heavy metals.

Comprehensive analysis of the stress associated protein (SAP) gene family in Tamarix hispida and the function of ThSAP6 in salt tolerance

Stress associated proteins (SAPs), a class of A20/AN1 zinc finger domain-containing proteins, are involved in a variety of biotic and abiotic stress responses in plants. However, little is known about the SAP gene family and their functions in Tamarix hispida. In this study, we isolated and characterized 11 SAPs from T. hispida. The expression patterns of ThSAPs were analyzed under various stresses (salt and drought) and phytohormone treatment (SA, ABA and MeJA) using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Most ThSAPs exhibited transcriptional responses to abiotic stresses and phytohormones. Among these ThSAPs, ThSAP6 was significantly induced by salt stress. Gain-and loss-of-function analyses revealed that ThSAP6 was a positive regulator of salt stress response. Overexpression of ThSAP6 in T. hispida increased antioxidant enzymes activity and proline content and decreased reactive oxygen species (ROS) accumulation and cell membrane damage under salt stress, while the opposite physiological changes were observed in ThSAP6-RNAi (RNA interference) lines. This study provides a comprehensive description of the SAP gene family in T. hispida, and demonstrates that ThSAP6 is a potential candidate for biotechnological approaches to improve salt tolerance in plants.

Increased Cuticle Waxes by Overexpression of WSD1 Improves Osmotic Stress Tolerance in Arabidopsis thaliana and Camelina sativa

To ensure global food security under the changing climate, there is a strong need for developing ‘climate resilient crops’ that can thrive and produce better yields under extreme environmental conditions such as drought, salinity, and high temperature. To enhance plant productivity under the adverse conditions, we constitutively overexpressed a bifunctional wax synthase/acyl-CoA:diacylglycerol acyltransferase (WSD1) gene, which plays a critical role in wax ester synthesis in Arabidopsis stem and leaf tissues. The qRT-PCR analysis showed a strong upregulation of WSD1 transcripts by mannitol, NaCl, and abscisic acid (ABA) treatments, particularly in Arabidopsis thaliana shoots. Gas chromatography and electron microscopy analyses of Arabidopsis seedlings overexpressing WSD1 showed higher deposition of epicuticular wax crystals and increased leaf and stem wax loading in WSD1 transgenics compared to wildtype (WT) plants. WSD1 transgenics exhibited enhanced tolerance to ABA, mannitol, drought and salinity, which suggested new physiological roles for WSD1 in stress response aside from its wax synthase activity. Transgenic plants were able to recover from drought and salinity better than the WT plants. Furthermore, transgenics showed reduced cuticular transpirational rates and cuticle permeability, as well as less chlorophyll leaching than the WT. The knowledge from Arabidopsis was translated to the oilseed crop Camelina sativa (L.) Crantz. Similar to Arabidopsis, transgenic Camelina lines overexpressing WSD1 also showed enhanced tolerance to drought stress. Our results clearly show that the manipulation of cuticular waxes will be advantageous for enhancing plant productivity under a changing climate.

Genomic characterization and expression profiles of stress-associated proteins (SAPs) in castor bean (Ricinus communis)

Stress-associated proteins (SAPs) are known as response factors to multiple abiotic and biotic stresses in plants. However, the potential physiological and molecular functions of SAPs remain largely unclear. Castor bean (Ricinus communis L.) is one of the most economically valuable non-edible woody oilseed crops, able to be widely cultivated in marginal lands worldwide because of its broad adaptive capacity to soil and climate conditions. Whether SAPs in castor bean plays a key role in adapting diverse soil conditions and stresses remains unknown. In this study, we used the castor bean genome to identify and characterize nine castor bean SAP genes (RcSAP). Structural analysis showed that castor bean SAP gene structures and functional domain types vary greatly, differing in intron number, protein sequence, and functional domain type. Notably, the AN1-C2H2-C2H2 zinc finger domain within RcSAP9 has not been often observed in other plant families. High throughput RNA-seq data showed that castor bean SAP gene profiles varied among different tissues. In addition, castor bean SAP gene expression varied in response to different stresses, including salt, drought, heat, cold and ABA and MeJA, suggesting that the transcriptional regulation of castor bean SAP genes might operate independently of each other, and at least partially independent from ABA and MeJA signal pathways. Cis-element analyses for each castor bean SAP gene showed that no common cis-elements are shared across the nine castor bean SAP genes. Castor bean SAPs were localized to different regions of cells, including the cytoplasm, nucleus, and cytomembrane. This study provides a comprehensive profile of castor bean SAP genes that advances our understanding of their potential physiological and molecular functions in regulating growth and development and their responses to different abiotic stresses.

Cloning and Characterization of TaSAP7-A, a Member of the Stress-Associated Protein Family in Common Wheat

Stress association proteins (SAPs) are A20/AN1 zinc-finger domain proteins, which play important roles in plant adaptation to abiotic stress and plant development. The functions of SAPs in some plants were reported, but little is known about it in wheat (Triticum aestivum L.). In this study, we characterized a novel 2AN1-type stress association protein gene TaSAP7-A, which was mapped to chromosome 5A in wheat. Subcellular localization indicated that TaSAP7-A was distributed in the nucleus and cytoplasm. Unlike previously known A20/AN1-type SAP genes, TaSAP7-A was negatively regulated to abiotic stress tolerance. Overexpressing TaSAP7-A Arabidopsis lines were hypersensitive to ABA, osmotic and salt stress at germination stage and post-germination stage. Overexpression of TaSAP7-A Arabidopsis plants accelerated the detached leaves' chlorophyll degradation. Association analysis of TaSAP7-A haplotypes and agronomic traits showed that Hap-5A-2 was significantly associated with higher chlorophyll content at jointing stage and grain-filling stage. These results jointly revealed that TaSAP7-A is related to the chlorophyll content in the leaves of Arabidopsis and wheat. Both in vivo and in vitro experiments demonstrated that TaSAP7-A interacted with TaS10B, which was the component of regulatory subunit in 26S proteasome. In general, TaSAP7-A was a regulator of chlorophyll content, and favorable haplotypes should be helpful for improving plant chlorophyll content and grain yield of wheat.

Multi-metal tolerance of DHHC palmitoyl transferase-like protein isolated from metal contaminated soil

The microbiota inhabiting in metal polluted environment develops strong defense mechanisms to combat pollution and sustain life. Investigating the functional genes of the eukaryotic microbiota inhabiting in these environments by using metatranscriptomics approach was the focus of this study. Size fractionated eukaryotic cDNA libraries (library A, < 0.5 kb, library B, 0.5-1.0 kb, and library C, > 1.0 kb) were constructed from RNA isolated from the metal contaminated soil. The library C was screened for Cadmium (Cd) tolerant genes by using Cd sensitive yeast mutant ycf1^Δ by functional complementation assay, which yielded various clones capable of growing in Cd amended media. One of the Cd tolerant clones, PLCg39 was selected because of its ability to grow at high concentrations of Cd. Sequence analysis of PLCg39 showed homology with DHHC palmitoyl transferases, which are responsible for addition of palmitoyl groups to proteins and usually possess metal coordination domains. The cDNA PLCg39 was able to confer tolerance to Cd-sensitive (ycf1^Δ), Copper-sensitive (cup1^Δ) and Zn-sensitive (zrc1^Δ) yeast mutants when grown at different concentrations of Cd (40-100 μM), Cu (150-1000 μM) and Zn (10-13 mM), respectively. The DHHC mutant akr1^Δ transformed with PLCg39 rescued from the metal sensitivity indicating the role of DHHC palmitoyl transferase in metal tolerance. This study demonstrated that PLCg39 acts as a potential metal tolerant gene which could be used in bioremediation, biosensing and other biotechnological fields.

Identification, gene expression and genetic polymorphism of zinc finger A20/AN1 stress-associated genes, HvSAP, in salt stressed barley from Kazakhstan

BACKGROUND

A family of genes designated as the Zinc finger A20/AN1 Transcription factors encoding stress-associated proteins (SAP) are well described in Arabidopsis and rice, and include 14 AtSAP and 18 OsSAP genes that are associated with variable tolerances to multiple abiotic stresses. The SAP gene family displays a great diversity in its structure and across different plant species. The aim of this study was to identify all HvSAP genes in barley (Hordeum vulgare L.), to analyse the expression of selected genes in response to salinity in barley leaves and develop SNP marker for HvSAP12 to evaluate the association between genotypes of barley plants and their grain yield in field trials.

RESULTS

In our study, 17 HvSAP genes were identified in barley, which were strongly homologous to rice genes. Five genes, HvSAP5, HvSAP6, HvSAP11, HvSAP12 and HvSAP15, were found to be highly expressed in leaves of barley plants in response to salt stress in hydroponics compared to controls, using both semi-quantitative RT-PCR and qPCR analyses. The Amplifluor-like SNP marker KATU-B30 was developed and used for HvSAP12 genotyping. A strong association (R² = 0.85) was found between KATU-B30 and grain yield production per plant of 50 F₃ breeding lines originating from the cross Granal × Baisheshek in field trials with drought and low to moderate salinity in Northern and Central Kazakhstan.

CONCLUSIONS

A group of HvSAP genes, and HvSAP12 in particular, play an important role in the tolerance of barley plants to salinity and drought, and is associated with higher grain yield in field trials. Marker-assisted selection with SNP marker KATU-B30 can be applied in barley breeding to improve grain yield production under conditions of abiotic stress.

Global transcriptome analysis of novel stress associated protein (SAP) genes expression dynamism of combined abiotic stresses in Oryza sativa (L.)

Genes encoding proteins with A20/AN1 zinc-finger domains, belonging to the stress associated protein (SAP) gene family, are present in all eukaryotes and play a decisive role in plant response to diverse physiological and molecular activities particularly on biotic and abiotic stresses (AbS). In this first and foremost study, global transcriptome analysis of members of the SAP gene family was carried out in C3 model-Oryza sativa (OsSAP) aiming at the identification of OsSAP genes activated in response to unique or Combined AbS (CAbS). Based on the available spatio-temporal and phytohormonal RNA-Seq expression profile datasets, nine OsSAP genes were filtered out and identified by a differential expression signature noted in various tissues as well as plant hormones. Comparative genome ideogram of OsSAP genes confirmed the orthologous collinearity with C4 panicoid genomes. Interactome of these genes, revealed the molecular cross-talks of OsSAP. Thus, the computational expression signature of OsSAP genes led to a better understanding of gene dynamism in diverse developmental tissues/organs. Transcriptional regulation analysis of key OsSAP genes in response to stress (drought and salinity) suggested the novel role of OsSAP1, OsSAP2, OsSAP5, OsSAP7, OsSAP8 and OsSAP11 in AbS. Altogether, the study provides deeper insights on molecular characteristics of OsSAP genes, which could be deployed further to decipher their precise functional roles in AbS responses.Communicated by Ramaswamy H. Sarma.

Last-Generation Genome-Environment Associations Reveal the Genetic Basis of Heat Tolerance in Common Bean (Phaseolus vulgaris L.)

Genome-environment associations (GEAs) are a powerful strategy for the study of adaptive traits in wild plant populations, yet they still lack behind in the use of modern statistical methods as the ones suggested for genome-wide association studies (GWASs). In order to bridge this gap, we couple GEA with last-generation GWAS algorithms in common bean to identify novel sources of heat tolerance across naturally heterogeneous ecosystems. Common bean (Phaseolus vulgaris L.) is the most important legume for human consumption, and breeding it for resistance to heat stress is key because annual increases in atmospheric temperature are causing decreases in yield of up to 9% for every 1°C. A total of 78 geo-referenced wild accessions, spanning the two gene pools of common bean, were genotyped by sequencing (GBS), leading to the discovery of 23,373 single-nucleotide polymorphism (SNP) markers. Three indices of heat stress were developed for each accession and inputted in last-generation algorithms (i.e. SUPER, FarmCPU, and BLINK) to identify putative associated loci with the environmental heterogeneity in heat stress. Best-fit models revealed 120 significantly associated alleles distributed in all 11 common bean chromosomes. Flanking candidate genes were identified using 1-kb genomic windows centered in each associated SNP marker. Some of these genes were directly linked to heat-responsive pathways, such as the activation of heat shock proteins (MED23, MED25, HSFB1, HSP40, and HSP20). We also found protein domains related to thermostability in plants such as S1 and Zinc finger A20 and AN1. Other genes were related to biological processes that may correlate with plant tolerance to high temperature, such as time to flowering (MED25, MBD9, and PAP), germination and seedling development (Pkinase_Tyr, Ankyrin-B, and Family Glicosil-hydrolase), cell wall stability (GAE6), and signaling pathway of abiotic stress via abscisic acid (histone-like transcription factors NFYB and phospholipase C) and auxin (Auxin response factor and AUX_IAA). This work offers putative associated loci for marker-assisted and genomic selection for heat tolerance in common bean. It also demonstrates that it is feasible to identify genome-wide environmental associations with modest sample sizes by using a combination of various carefully chosen environmental indices and last-generation GWAS algorithms.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

A stress-associated protein, LmSAP, from the halophyte Lobularia maritima provides tolerance to heavy metals in tobacco through increased ROS scavenging and metal detoxification processes

Agricultural soil pollution by heavy metals is a severe global ecological problem. We recently showed that overexpression of LmSAP, a member of the stress-associated protein (SAP) gene family isolated from Lobularia maritima, in transgenic tobacco led to enhanced tolerance to abiotic stress. In this study, we characterised the response of LmSAP transgenic tobacco plants to metal stresses (cadmium (Cd), copper (Cu), manganese (Mn), and zinc (Zn)). In L. maritima, LmSAP expression increased after 12 h of treatment with these metals, suggesting its involvement in the plant response to heavy metal stress. LmSAP transgenic tobacco plants subjected to these stress conditions were healthy, experienced higher seedling survival rates, and had longer roots than non-transgenic plants (NT). However, they exhibited higher tolerance towards cadmium and manganese than towards copper and zinc. LmSAP-overexpressing tobacco seedlings accumulated more cadmium, copper, and manganese compared with NT plants, but displayed markedly decreased hydrogen peroxide (H2O2) and lipid peroxidation levels after metal treatment. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were significantly higher in transgenic plants than in NT plants after exposure to metal stress. LmSAP overexpression also enhanced the transcription of several genes encoding metallothioneins (Met1, Met2, Met3, Met4, and Met5), a copper transport protein CCH, a Cys and His-rich domain-containing protein RAR1 (Rar1), and a ubiquitin-like protein 5 (PUB1), which are involved in metal tolerance in tobacco. Our findings indicate that LmSAP overexpression in tobacco enhanced tolerance to heavy metal stress by protecting the plant cells against oxidative stress, scavenging reactive oxygen species (ROS), and decreasing the intracellular concentration of free heavy metals through its effect on metal-binding proteins in the cytosol.

The LmSAP gene isolated from the halotolerant Lobularia maritima improves salt and ionic tolerance in transgenic tobacco lines

The A20/AN1 zinc-finger domain-containing proteins of the stress-associated proteins (SAPs) family are fast emerging as potential candidates for biotechnological approaches to improve abiotic stress tolerance in plants. We identified LmSAP, one of the SAPs genes in Lobularia maritima (L.) Desv., a halophyte brassicaceae, through its transcript accumulation in response to salinity and ionic stresses. Sequence homology analysis revealed that LmSAP contains two conserved zinc-finger domains A20 and AN1. Phylogeny analyses showed that LmSAP exhibited high amino acid sequence identity to other plant SAPs. Heterologous expression of LmSAP in yeast increased cell tolerance to salt and osmotic stress. In addition, the overexpression of LmSAP conferred high salt and ionic tolerance to transgenic tobacco plants. Transgenic tobacco seedlings showed higher survival rates and antioxidant activities under salt and ionic stresses. Enhanced antioxidant activities paralleled lower malondialdehyde and superoxide anion O2- levels in the LmSAP transgenic seedlings. Overall, our results suggest that overexpression of LmSAP enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stresses.

Heavy Metals Induce Iron Deficiency Responses at Different Hierarchic and Regulatory Levels

In plants, the excess of several heavy metals mimics iron (Fe) deficiency-induced chlorosis, indicating a disturbance in Fe homeostasis. To examine the level at which heavy metals interfere with Fe deficiency responses, we carried out an in-depth characterization of Fe-related physiological, regulatory, and morphological responses in Arabidopsis (Arabidopsis thaliana) exposed to heavy metals. Enhanced zinc (Zn) uptake closely mimicked Fe deficiency by leading to low chlorophyll but high ferric-chelate reductase activity and coumarin release. These responses were not caused by Zn-inhibited Fe uptake via IRON-REGULATED TRANSPORTER (IRT1). Instead, Zn simulated the transcriptional response of typical Fe-regulated genes, indicating that Zn affects Fe homeostasis at the level of Fe sensing. Excess supplies of cobalt and nickel altered root traits in a different way from Fe deficiency, inducing only transient Fe deficiency responses, which were characterized by a lack of induction of the ethylene pathway. Cadmium showed a rather inconsistent influence on Fe deficiency responses at multiple levels. By contrast, manganese evoked weak Fe deficiency responses in wild-type plants but strongly exacerbated chlorosis in irt1 plants, indicating that manganese antagonized Fe mainly at the level of transport. These results show that the investigated heavy metals modulate Fe deficiency responses at different hierarchic and regulatory levels and that the interaction of metals with physiological and morphological Fe deficiency responses is uncoupled. Thus, this study not only emphasizes the importance of assessing heavy metal toxicities at multiple levels but also provides a new perspective on how Fe deficiency contributes to the toxic action of individual heavy metals.

Dual regulation of water retention and cell growth by a stress-associated protein (SAP) gene in Prunus

We have identified a gene (PpSAP1) of Prunus persica coding for a stress-associated protein (SAP) containing Zn-finger domains A20 and AN1. SAPs have been described as regulators of the abiotic stress response in plant species, emerging as potential candidates for improvement of stress tolerance in plants. PpSAP1 was highly expressed in leaves and dormant buds, being down-regulated before bud dormancy release. PpSAP1 expression was moderately induced by water stresses and heat in buds. In addition, it was found that PpSAP1 strongly interacts with polyubiquitin proteins in the yeast two-hybrid system. The overexpression of PpSAP1 in transgenic plum plants led to alterations in leaf shape and an increase of water retention under drought stress. Moreover, we established that leaf morphological alterations were concomitant with a reduced cell size and down-regulation of genes involved in cell growth, such as GROWTH-REGULATING FACTOR (GRF)1-like, TONOPLAST INTRINSIC PROTEIN (TIP)-like, and TARGET OF RAPAMYCIN (TOR)-like. Especially, the inverse expression pattern of PpSAP1 and TOR-like in transgenic plum and peach buds suggests a role of PpSAP1 in cell expansion through the regulation of TOR pathway.

Epiallelic changes in known stress-responsive genes under extreme drought conditions in Brassica juncea (L.) Czern

Under severe drought conditions, Brassica juncea shows differential methylation and demethylation events, such that certain epialleles are silenced and some are activated. The plant employed avoidance strategy by delaying apoptosis through the activation of several genes. Harsh environmental conditions pose serious threat to normal growth and development of crops, sometimes leading to their death. However, plants have developed an essential mechanism of modulation of gene activities by epigenetic modifications. Brassica juncea is an important oilseed crop contributing effectively to the economy of India. In the present investigation, we studied the changes in the methylation level of various stress-responsive genes of B. juncea variety RH30 by methylation-dependent immune-precipitation-chip in response to severe drought. On the basis of changes in the number of differential methylation regions in response to drought, the promoter regions were designated as hypermethylated and hypomethylated. Gene body methylation increased in all the genes, whereas promoter methylation was dependent on the function of the gene. Overall, the genes responsible for delaying apoptosis were hypomethylated and many genes responsible for normal routine activities were hypermethylated at promoter regions, thereby suggesting that these may be suspending the activities under harsh conditions.

Isolation and characterization of LcSAP, a Leymus chinensis gene which enhances the salinity tolerance of Saccharomyces cerevisiae

A number of members of the SAP ("stress-associated protein") gene family have been implicated in the plant stress response. Here, a SAP gene has been isolated using PCR RACE from the perennial grass Leymus chinensis, a species which has reputation for ecological adaptability. The 17.6 kDa LcSAP product comprised 161 residues, including both an A20 domain and an AN1 domain, a feature of type I SAPs. Using a semi-quantitative RT-PCR assay to profile its transcription, it was shown that LcSAP was more strongly transcribed in the leaf than in the root under control conditions. The level of LcSAP transcription began to rise 6 h after the plant's exposure to 400 mM NaCl, and the abundance of transcript remained stable for at least 24 h. Exposing the plant to 100 mM Na₂CO₃ also induced LcSAP transcription, but the abundance of SAP transcript faded after 6 h. When LcSAP was introduced into yeast cells, the transgenic cells grew better than wild type ones when the medium contained 1.4 M NaCl. The ability of LcSAP to respond to salinity stress in yeast suggests that it also makes a contribution to the stress tolerance shown by L. chinensis.

Transcriptomic analysis reveals key early events of narciclasine signaling in Arabidopsis root apex

Histochemical staining and RNA-seq data demonstrated that the ROS- and plant hormone-regulated stress responses are the key early events of narciclasine signaling in Arabidopsis root cells. Narciclasine, an amaryllidaceae alkaloid isolated from Narcissus tazetta bulbs, employs a broad range of functions on plant development and growth. However, its molecular interactions that modulate these roles in plants are not fully understood. To elucidate the global responses of Arabidopsis roots to short-term narciclasine exposure, we first measured the accumulation of H₂O₂ and O₂^- with histochemical staining, and then profiled the gene expression pattern in Arabidopsis root tips treated with 0.5 µM narciclasine across different exposure times by RNA-seq. Physiological measurements showed a significant increase in H₂O₂ began at 30-60 min of narciclasine treatment and O₂^- accumulated by 120 min. Compared with controls, 236 genes were upregulated and 54 genes were downregulated with 2 h of narciclasine treatment, while 968 genes were upregulated and 835 genes were downregulated with 12 h of treatment. The Gene Ontology analysis revealed that the differentially expressed genes were highly enriched during oxidative stress, including those involved in the "regulation of transcription", "response to oxidative stress", "plant-pathogen interaction", "ribonucleotide binding", "plant cell wall organization", and "ribosome biogenesis". Moreover, Kyoto Encyclopedia of Genes and Genomes pathway enrichment statistics suggested that carbohydrate metabolism, amino acid metabolism, amino sugar and nucleotide sugar metabolism, and biosynthesis of phenylpropanoid and secondary metabolites were significantly inhibited by 12 h of narciclasine exposure. Hence, our results demonstrate that hormones and H₂O₂ are important regulators of narciclasine signaling and help to uncover the factors involved in the molecular interplay between narciclasine and phytohormones in Arabidopsis root cells.

Genome-wide identification and expression analysis of stress-associated proteins (SAPs) containing A20/AN1 zinc finger in cotton

Stress-associated proteins (SAPs) containing the A20/AN1 zinc-finger domain play important roles in response to both biotic and abiotic stresses in plants. Nevertheless, few studies have focused on the SAP gene family in cotton. To explore the distributions and expression patterns of these genes, we performed genome-wide identification and characterization of SAPs in tetraploid Gossypium hirsutum L. TM-1 (AD1). A total of 37 genes encoding SAPs were identified, 36 of which were duplicated in the A and D sub-genomes. The analysis of gene architectures and conserved protein motifs revealed that nearly all A20-AN1-type SAPs were intron-free, whereas AN1-AN1-type SAPs contained one intron. The cis-elements of the SAP promoters were studied, as were the expression levels of cotton SAP genes under different stresses based on RNA-seq data and validated by qRT-PCR. Most cotton SAP genes were induced by multiple stresses and phytohormones, particularly salt stress, indicating that SAP genes may play important roles in cotton's response to unfavorable environmental changes. Among these identified SAPs, the expression of GhSAP17A/D is suppressed in cotton response to Vertillium dahliae, and the GhSAP17A/D-silenced cotton exhibits more resistance to V. dahliae. This study provides insight into the evolution of SAP genes in upland cotton and may aid in efforts at further functional identification of A20/AN1-type proteins and cotton's response to different stresses.

Expression of cadR Enhances its Specific Activity for Cd Detoxification and Accumulation in Arabidopsis

Cadmium (Cd) is a transition metal that is highly toxic in biological systems. Anthropogenic emissions of Cd have increased biogeochemical cycling and the amount of Cd in the biosphere. Here we studied the utility of a bacterial Cd-binding protein, CadR, for the remediation of Cd contamination. CadR was successfully targeted to chloroplasts using a constitutive Cauliflower mosaic virus (CaMV) 35S promoter or a shoot-specific Chl a/b-binding protein 2 gene (CAB2) promoter and an RbcS (small subunit of the Rubisco complex) transit peptide. Under short-term (2 d) exposure to Cd, the cadR transgenic plants showed up to a 2.9-fold Cd accumulation in roots compared with untransformed plants. Under medium term (7 d) exposure to Cd, the concentrations of Cd in leaves began to increase but there were no differences between the wild type and the cadR transgenic plants. Under long-term (16 d) exposure to Cd, the cadR transgenic plants accumulated greater amounts of Cd in leaves than the untransformed plants. Total Cd accumulation (µg per plant) in shoots and roots of the plants expressing cadR were significantly higher (up to 3.5-fold in shoots and 5.2-fold in roots) than those of the untransformed plants. We also found that targeting CadR to chloroplasts facilitated chloroplastic metal homeostasis and Chl b accumulation. Our results demonstrate that manipulating chelating capacity in chloroplasts or in the cytoplasm may be effective in modifying both the accumulation of and resistance to Cd.

Laminarin modulates the chloroplast antioxidant system to enhance abiotic stress tolerance partially through the regulation of the defensin-like gene expression

Algae wall polysaccharide, laminarin (Lam), has an established role on induction of plant disease resistance. In this study, application of Lam increased Arabidopsis fresh weight and enhanced tolerance to salt and heat stress by stabilizing chloroplast under adverse environment. Transcriptome analysis indicated that, in addition to induced a large number of genes associated with the host defense, genes involved in the regulation of abiotic stress tolerance mostly the heat stress response constituted the largest group of the up-regulated genes. Lam induced expression of IRT1, ZIP8, and copper transporters involved in transport of Fe, Zn, Cu ions associated with the activity of chloroplast antioxidant system. Lam also up-regulated genes involved in the synthesis of terpenoid, a plastidial-derived secondary metabolite with antioxidant activity. Overexpression of a Lam-induced defensin like 202 (DEFL202) resulted in increased chloroplast stability under salt stress and increased plant growth activity after heat stress. Expression of antioxidant enzymes including SOD and ascorbate peroxidase (APX), photosystem PsbA-D1 and ABA-dependent responsive to desiccation 22 (RD22) was induced to higher levels in the transgenic seedlings. In sum, our results suggest that Lam is an potent inducer for induction of chloroplastic antioxidant activity. Lam affect plant abiotic stress tolerance partially through regulation of the DEFL-mediated pathway.

Silicon-induced reversibility of cadmium toxicity in rice

Silicon (Si) modulates tolerance to abiotic stresses, but little is known about the reversibility of stress effects by supplementing previously stressed plants with Si. This is surprising since recovery experiments might allow mechanisms of Si-mediated amelioration to be addressed. Rice was exposed to 10 µM CdCl2 for 4 d in hydroponics, followed by 0.6mM Si(OH)4 supplementation for 4 d. Si reversed the effects of Cd, as reflected in plant growth, photosynthesis, elemental composition, and some biochemical parameters. Cd-dependent deregulation of nutrient homeostasis was partially reversed by Si supply. Photosynthetic recovery within 48h following Si supply, coupled with strong stimulation of the ascorbate-glutathione system, indicates efficient activation of defense. The response was further verified by transcript analyses with emphasis on genes encoding members of the stress-associated protein (SAP) family. The transcriptional response to Cd was mostly reversed following Si supply. Reprogramming of the Cd response was obvious for Phytochelatin synthase 1, SAP1 , SAP14, and the transcription factor genes AP2/Erf020, Hsf31, and NAC6 whose transcript levels were strongly activated in roots of Cd-stressed rice, but down-regulated in the presence of Si. These findings, together with changes in biochemical parameters, highlight the significance of Si in growth recovery of Cd-stressed rice and indicate a decisive role for readjusting cell redox homeostasis.

Oligouridylate Binding Protein 1b Plays an Integral Role in Plant Heat Stress Tolerance

Stress granules (SGs), which are formed in the plant cytoplasm under stress conditions, are transient dynamic sites (particles) for mRNA storage. SGs are actively involved in protecting mRNAs from degradation. Oligouridylate binding protein 1b (UBP1b) is a component of SGs. The formation of microscopically visible cytoplasmic foci, referred to as UBP1b SG, was induced by heat treatment in UBP1b-overexpressing Arabidopsis plants (UBP1b-ox). A detailed understanding of the function of UBP1b, however, is still not clear. UBP1b-ox plants displayed increased heat tolerance, relative to control plants, while ubp1b mutants were more sensitive to heat stress than control plants. Microarray analysis identified 117 genes whose expression was heat-inducible and higher in the UBP1b-ox plants. RNA decay analysis was performed using cordycepin, a transcriptional inhibitor. In order to determine if those genes serve as targets of UBP1b, the rate of RNA degradation of a DnaJ heat shock protein and a stress-associated protein (AtSAP3) in UBP1b-ox plants was slower than in control plants; indicating that the mRNAs of these genes were protected within the UBP1b SG granule. Collectively, these data demonstrate that UBP1b plays an integral role in heat stress tolerance in plants.

The promoter of the AlSAP gene from the halophyte grass Aeluropus littoralis directs a stress-inducible expression pattern in transgenic rice plants

When fused to " Pr AlSAP " promoter, transcripts of gusA exhibited similar accumulation patterns in transgenic rice as AlSAP transcripts in A. littoralis. Pr AlSAP can be used for engineering abiotic stress tolerance. We previously showed that ectopic expression of a stress-associated protein gene from Aeluropus littoralis (AlSAP) enhances tolerance to multiple abiotic stresses in tobacco, wheat and rice. The ortholog of AlSAP in rice is OsSAP9. Here, we demonstrate that AlSAP transcripts accumulate in Aeleuropus in response to multiple abiotic stresses and at a higher level in roots, while those of OsSAP9 are preferentially induced by cold and heat treatments and accumulate preferentially in leaves of rice. In silico analysis of the AlSAP promoter "Pr AlSAP " predicted several cis-acting elements responsible for gene regulation by dehydration, salt, heat, ABA, SA, wounding and tissue-specific expression. The Pr AlSAP promoter was fused to the gusA gene and used to produce transgenic rice plants. Transcripts of gusA exhibited similar accumulation patterns in transgenic rice as AlSAP transcripts in A. littoralis. Indeed, accumulation of gusA transcripts was higher in roots than in leaves and induced by salt, drought, cold and heat treatments. GUS activity was confirmed in roots, coleoptiles, leaves and glumes, but absent in the root cell elongation zone and in dry seeds. A wound treatment strongly induced GUS accumulation in leaves and imbibed seeds. Altogether, these results indicate that the regulatory regions of two ortholog genes "AlSAP" and "OsSAP9" have diverged in the specificity of the signals promoting their induction, but that the trans-acting elements allowing the correct spatiotemporal regulation and stress induction of Pr AlSAP exist in rice. Therefore, the AlSAP promoter appears to be an interesting candidate for engineering abiotic stress tolerance in cereals.

Regulatory functions of evolutionarily conserved AN1/A20-like Zinc finger family proteins in Arabidopsis stress responses under high temperature

AN1/A20-like Zinc finger family proteins are evolutionarily conserved regulatory components in eukaryotic signaling circuits. In Arabidopsis thaliana, the AN1/A20 Zinc finger family is encoded as 14 members in the genome and collectively referred to as stress-associated proteins (SAPs). Here we described AtSAP5 localized to the nucleus, and played a role in heat-responsive gene regulation together with MBF1c. Seedling survival assay of sap5 and mbf1c demonstrated consistent effects of AtSAP5 and MBF1C in response to two-step heat treatment, supporting their function in heat stress tolerance. Our findings yield an insight in A20/AN1-like Zinc finger protein AtSAP5 functions in plant adaptability under high temperature.

OsiSAP1 overexpression improves water-deficit stress tolerance in transgenic rice by affecting expression of endogenous stress-related genes

OsiSAP1, an A20/AN1 zinc-finger protein, confers water-deficit stress tolerance at different stages of growth by affecting expression of several endogenous genes in transgenic rice. Transgenic lines have been generated from rice constitutively expressing OsiSAP1, an A20/AN1 zinc-finger containing stress-associated protein gene from rice, driven by maize UBIQUITIN gene promoter and evaluated for water-deficit stress tolerance at different stages of growth. Their seeds show early germination and seedlings grow better under water-deficit stress compared to non-transgenic (NT) rice. Leaves from transgenic seedlings showed lesser membrane damage and lipid peroxidation under water-deficit stress. Relatively lower rate of leaf water loss has been observed in detached intact leaves from transgenic plants during late vegetative stage. Delayed leaf rolling and higher relative water content were also observed in transgenic plants under progressive water-deficit stress during reproductive developmental stage. Although reduction in grain yield is observed under unstressed condition, the relative water-deficit stress-induced yield losses are lower in transgenic rice vis-à-vis NT plants thereby resulting in yield loss protection. Transcriptome analysis suggests that overexpression of OsiSAP1 in transgenic rice results in altered expression of several endogenous genes including those coding for transcription factors, membrane transporters, signaling components and genes involved in metabolism, growth and development. A total of 150 genes were found to be more than twofold up-regulated in transgenic rice of which 43 genes are known to be involved in stress response. Our results suggest that OsiSAP1 is a positive regulator of water-deficit stress tolerance in rice.

A heavy metal-associated protein (AcHMA1) from the halophyte, Atriplex canescens (Pursh) Nutt., confers tolerance to iron and other abiotic stresses when expressed in Saccharomyces cerevisiae

Many heavy metals are essential for metabolic processes, but are toxic at elevated levels. Metal tolerance proteins provide resistance to this toxicity. In this study, we identified and characterized a heavy metal-associated protein, AcHMA1, from the halophyte, Atriplex canescens. Sequence analysis has revealed that AcHMA1 contains two heavy metal binding domains. Treatments with metals (Fe, Cu, Ni, Cd or Pb), PEG6000 and NaHCO3 highly induced AcHMA1 expression in A. canescens, whereas NaCl and low temperature decreased its expression. The role of AcHMA1 in metal stress tolerance was examined using a yeast expression system. Expression of the AcHMA1 gene significantly increased the ability of yeast cells to adapt to and recover from exposure to excess iron. AcHMA1 expression also provided salt, alkaline, osmotic and oxidant stress tolerance in yeast cells. Finally, subcellular localization of an AcHMA1/GFP fusion protein expressed in tobacco cells showed that AcHMA1 was localized in the plasma membrane. Thus, our results suggest that AcHMA1 encodes a membrane-localized metal tolerance protein that mediates the detoxification of iron in eukaryotes. Furthermore, AcHMA1 also participates in the response to abiotic stress.

Molecular characterization of Alr1105 a novel arsenate reductase of the diazotrophic cyanobacterium Anabaena sp. PCC7120 and decoding its role in abiotic stress management in Escherichia coli

This paper constitutes the first report on the Alr1105 of Anabaena sp. PCC7120 which functions as arsenate reductase and phosphatase and offers tolerance against oxidative and other abiotic stresses in the alr1105 transformed Escherichia coli. The bonafide of 40.8 kDa recombinant GST+Alr1105 fusion protein was confirmed by immunoblotting. The purified Alr1105 protein (mw 14.8 kDa) possessed strong arsenate reductase (Km 16.0 ± 1.2 mM and Vmax 5.6 ± 0.31 μmol min⁻¹ mg protein⁻¹) and phosphatase activity (Km 27.38 ± 3.1 mM and Vmax 0.077 ± 0.005 μmol min⁻¹ mg protein⁻¹) at an optimum temperature 37 °C and 6.5 pH. Native Alr1105 was found as a monomeric protein in contrast to its homologous Synechocystis ArsC protein. Expression of Alr1105 enhanced the arsenic tolerance in the arsenate reductase mutant E. coli WC3110 (∆arsC) and rendered better growth than the wild type W3110 up to 40 mM As (V). Notwithstanding above, the recombinant E. coli strain when exposed to CdCl₂, ZnSO₄, NiCl₂, CoCl₂, CuCl₂, heat, UV-B and carbofuron showed increase in growth over the wild type and mutant E. coli transformed with the empty vector. Furthermore, an enhanced growth of the recombinant E. coli in the presence of oxidative stress producing chemicals (MV, PMS and H₂O₂), suggested its protective role against these stresses. Appreciable expression of alr1105 gene as measured by qRT-PCR at different time points under selected stresses reconfirmed its role in stress tolerance. Thus the Alr1105 of Anabaena sp. PCC7120 functions as an arsenate reductase and possess novel properties different from the arsenate reductases known so far.

The root of ABA action in environmental stress response

The growth and development of plants are influenced by the integration of diverse endogenous and environmental signals. Acting as a mediator of extrinsic signals, the stress hormone, abscisic acid (ABA), has been shown to regulate many aspects of plant development in response to unfavourable environmental stresses, allowing the plant to cope and survive in adverse conditions, such as drought, low or high temperature, or high salinity. Here, we summarize recent evidence on the roles of ABA in environmental stress responses in the Arabidopsis root; and on how ABA crosstalks with other phytohormones to modulate root development and growth in Arabidopsis. We also review literature findings showing that, in response to environmental stresses, ABA affects the root system architecture in other plant species, such as rice.

Medicago truncatula stress associated protein 1 gene (MtSAP1) overexpression confers tolerance to abiotic stress and impacts proline accumulation in transgenic tobacco

Stress associated proteins (SAP) have been already reported to play a role in tolerance acquisition of some abiotic stresses. In the present study, the role of MtSAP1 (Medicago truncatula) in tolerance to temperature, osmotic and salt stresses has been studied in tobacco transgenic seedlings. Compared to wild type, MtSAP1 overexpressors were less affected in their growth and development under all tested stress conditions. These results confirm that MtSAP1 is involved in the response processes to various abiotic constraints. In parallel, we have performed studies on an eventual link between MtSAP1 overexpression and proline, a major player in stress response. In an interesting way, the results for the transgenic lines did not show any increase of proline content under osmotic and salt stress, contrary to the WT which usually accumulated proline in response to stress. These data strongly suggest that MtSAP1 is not involved in signaling pathway responsible for the proline accumulation in stress conditions. This could be due to the fact that the overexpression of MtSAP1 provides sufficient tolerance to seedlings to cope with stress without requiring the free proline action. Beyond that, the processes by which the MtSAP1 overexpression lead to the suppression of proline accumulation will be discussed in relation with data from our previous study involving nitric oxide.

SAPs as novel regulators of abiotic stress response in plants

Stress associated proteins (SAPs), novel A20/AN1 zinc-finger domain-containing proteins, are fast emerging as potential candidates for biotechnological approaches in order to improve abiotic stress tolerance in plants - the ultimate aim of which is crop-yield protection. Until relatively recently, such proteins had only been identified in humans, where they had been shown to be key regulators of innate immunity. Their phylogenetic relationship and recruitment of diverse protein domains reflect an architectural and mechanistic diversity. Emerging evidence suggests that SAPs may act as ubiquitin ligase, redox sensor, and regulator of gene expression during stress. Here, we evaluate the new knowledge on SAPs with a view to understand their mechanism of action. Furthermore, we set an agenda for investigating hitherto unexplored roles of these proteins.

Generating high temperature tolerant transgenic plants: Achievements and challenges

Production of plants tolerant to high temperature stress is of immense significance in the light of global warming and climate change. Plant cells respond to high temperature stress by re-programming their genetic machinery for survival and reproduction. High temperature tolerance in transgenic plants has largely been achieved either by over-expressing heat shock protein genes or by altering levels of heat shock factors that regulate expression of heat shock and non-heat shock genes. Apart from heat shock factors, over-expression of other trans-acting factors like DREB2A, bZIP28 and WRKY proteins has proven useful in imparting high temperature tolerance. Besides these, elevating the genetic levels of proteins involved in osmotic adjustment, reactive oxygen species removal, saturation of membrane-associated lipids, photosynthetic reactions, production of polyamines and protein biosynthesis process have yielded positive results in equipping transgenic plants with high temperature tolerance. Cyclic nucleotide gated calcium channel proteins that regulate calcium influxes across the cell membrane have recently been shown to be the key players in induction of high temperature tolerance. The involvement of calmodulins and kinases in activation of heat shock factors has been implicated as an important event in governing high temperature tolerance. Unfilled gaps limiting the production of high temperature tolerant transgenic plants for field level cultivation are discussed.

MusaSAP1, a A20/AN1 zinc finger gene from banana functions as a positive regulator in different stress responses

A20/AN1 zinc finger domain containing Stress Associated Proteins (SAP) are involved in diverse stress response pathways in plants. In the present study, a novel banana SAP gene, MusaSAP1, was identified from banana EST database and was subsequently characterized by overexpression in transgenic banana plants. Expression profiling in native banana plants showed that MusaSAP1 was up-regulated by drought, salt, cold, heat and oxidative stress as well as by treatment with abscisic acid. Cellular localization assay carried out by making a MusaSAP1::GFP fusion protein indicated that MusaSAP1 is incompletely translocated to nucleus. Copy number analysis performed using real time PCR and Southern blotting indicated that MusaSAP1 occurs in the banana genome in a single copy per 11 chromosome set. Transgenic banana plants constitutively overexpressing MusaSAP1 displayed better stress endurance characteristics as compared to controls in both in vitro and ex vivo assays. Lesser membrane damage as indicated by reduced malondialdehyde levels in transgenic leaves subjected to drought, salt or oxidative stress pointed towards significant role for MusaSAP1 in stress amelioration pathways of banana. Strong up-regulation of a polyphenol oxidase (PPO) coding transcript in MusaSAP1 overexpressing plants together with induction of MusaSAP1 by wounding and methyl jasmonate treatment indicated possible involvement of MusaSAP1 in biotic stress responses where PPOs perform major functions in multiple defense pathways.

Overexpression of a Medicago truncatula stress-associated protein gene (MtSAP1) leads to nitric oxide accumulation and confers osmotic and salt stress tolerance in transgenic tobacco

The impact of Medicago truncatula stress-associated protein gene (MtSAP1) overexpression has been investigated in Nicotiana tabacum transgenic seedlings. Under optimal conditions, transgenic lines overexpressing MtSAP1 revealed better plant development and higher chlorophyll content as compared to wild type seedlings. Interestingly, transgenic lines showed a stronger accumulation of nitric oxide (NO), a signaling molecule involved in growth and development processes. This NO production seemed to be partially nitrate reductase dependent. Due to the fact that NO has been also reported to play a role in tolerance acquisition of plants to abiotic stresses, the responses of MtSAP1 overexpressors to osmotic and salt stress have been studied. Compared to the wild type, transgenic lines were less affected in their growth and development. Moreover, NO content in MtSAP1 overexpressors was always higher than that detected in wild seedlings under stress conditions. It seems that this better tolerance induced by MtSAP1 overexpression could be associated with this higher NO production that would enable seedlings to reach a high protection level to prepare them to cope with abiotic stresses.

The protein Zfand5 binds and stabilizes mRNAs with AU-rich elements in their 3'-untranslated regions

AU-rich elements (AREs) in the 3'-UTR of unstable transcripts play a vital role in the regulation of many inflammatory mediators. To identify novel ARE-dependent gene regulators, we screened a human leukocyte cDNA library for candidates that enhanced the activity of a luciferase reporter bearing the ARE sequence from TNF (ARE(TNF)). Among 171 hits, we focused on Zfand5 (zinc finger, AN1-type domain 5), a 23-kDa protein containing two zinc finger domains. Zfand5 expression was induced in macrophages in response to IFNγ and Toll-like receptor ligands. Knockdown of Zfand5 in macrophages decreased expression of ARE class II transcripts TNF and COX2, whereas overexpression stabilized TNF mRNA by suppressing deadenylation. Zfand5 specifically bound to ARE(TNF) mRNA and competed with tristetraprolin, a protein known to bind and destabilize class II ARE-containing RNAs. Truncation studies indicated that both zinc fingers of Zfand5 contributed to its mRNA-stabilizing function. These findings add Zfand5 to the growing list of RNA-binding proteins and suggest that Zfand5 can enhance ARE-containing mRNA stability by competing with tristetraprolin for mRNA binding.

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.