Improved drought and salt stress tolerance in transgenic tobacco overexpressing a novel A20/AN1 zinc-finger "AlSAP" gene isolated from the halophyte grass Aeluropus littoralis

Research progress on plant stress-associated protein (SAP) family: Master regulators to deal with environmental stresses

Every year, unfavorable environmental factors significantly affect crop productivity and threaten food security. Plants are sessile; they cannot move to escape unfavorable environmental conditions, and therefore, they activate a variety of defense pathways. Among them are processes regulated by stress-associated proteins (SAPs). SAPs have a specific zinc finger domain (A20) at the N-terminus and either AN1 or C2H2 at the C-terminus. SAP proteins are involved in many biological processes and in response to various abiotic or biotic constraints. Most SAPs play a role in conferring transgenic stress resistance and are stress-inducible. The emerging field of SAPs in abiotic or biotic stress response regulation has attracted the attention of researchers. Although SAPs interact with various proteins to perform their functions, the exact mechanisms of these interactions remain incompletely understood. This review aims to provide a comprehensive understanding of SAPs, covering their diversity, structure, expression, and subcellular localization. SAPs play a pivotal role in enabling crosstalk between abiotic and biotic stress signaling pathways, making them essential for developing stress-tolerant crops without yield penalties. Collectively, understanding the complex regulation of SAPs in stress responses can contribute to enhancing tolerance against various environmental stresses through several techniques such as transgenesis, classical breeding, or gene editing.

Rice A20/AN1 protein, OsSAP10, confers water-deficit stress tolerance via proteasome pathway and positive regulation of ABA signaling in Arabidopsis

KEY MESSAGE

Overexpression of rice A20/AN1 zinc-finger protein, OsSAP10, improves water-deficit stress tolerance in Arabidopsis via interaction with multiple proteins. Stress-associated proteins (SAPs) constitute a class of A20/AN1 zinc-finger domain containing proteins and their genes are induced in response to multiple abiotic stresses. The role of certain SAP genes in conferring abiotic stress tolerance is well established, but their mechanism of action is poorly understood. To improve our understanding of SAP gene functions, OsSAP10, a stress-inducible rice gene, was chosen for the functional and molecular characterization. To elucidate its role in water-deficit stress (WDS) response, we aimed to functionally characterize its roles in transgenic Arabidopsis, overexpressing OsSAP10. OsSAP10 transgenics showed improved tolerance to water-deficit stress at seed germination, seedling and mature plant stages. At physiological and biochemical levels, OsSAP10 transgenics exhibited a higher survival rate, increased relative water content, high osmolyte accumulation (proline and soluble sugar), reduced water loss, low ROS production, low MDA content and protected yield loss under WDS relative to wild type (WT). Moreover, transgenics were hypersensitive to ABA treatment with enhanced ABA signaling and stress-responsive genes expression. The protein-protein interaction studies revealed that OsSAP10 interacts with proteins involved in proteasomal pathway, such as OsRAD23, polyubiquitin and with negative and positive regulators of stress signaling, i.e., OsMBP1.2, OsDRIP2, OsSCP and OsAMTR1. The A20 domain was found to be crucial for most interactions but insufficient for all interactions tested. Overall, our investigations suggest that OsSAP10 is an important candidate for improving water-deficit stress tolerance in plants, and positively regulates ABA and WDS signaling via protein-protein interactions and modulation of endogenous genes expression in ABA-dependent manner.

Aeluropus littoralis stress-associated protein promotes water deficit resilience in engineered durum wheat

Global climate change-related water deficit negatively affect the growth, development and yield performance of multiple cereal crops, including durum wheat. Therefore, the improvement of water-deficit stress tolerance in durum wheat varieties in arid and semiarid areas has become imperative for food security. Herein, we evaluated the water deficiency resilience potential of two marker-free transgenic durum wheat lines (AlSAP-lines: K9.3 and K21.3) under well-watered and water-deficit stress conditions at both physiological and agronomic levels. These two lines overexpressed the AlSAP gene, isolated from the halophyte grass Aeluropus littoralis, encoding a stress-associated zinc finger protein containing the A20/AN1 domains. Under well-watered conditions, the wild-type (WT) and both AlSAP-lines displayed comparable performance concerning all the evaluated parameters. Ectopic transgene expression exerted no adverse effects on growth and yield performance of the durum wheat plants. Under water-deficit conditions, no significant differences in the plant height, leaf number, spike length, and spikelet number were observed between AlSAP-lines and WT plants. However, compared to WT, the AlSAP-lines exhibited greater dry matter production, greater flag leaf area, improved net photosynthetic rate, stomatal conductance, and water use efficiency. Notably, the AlSAP-lines displayed 25 % higher grain yield (GY) than the WT plants under water-deficit conditions. The RT-qPCR-based selected stress-related gene (TdDREB1, TdLEA, TdAPX1, and TdBlt101-2) expression analyses indicated stress-related genes enhancement in AlSAP-durum wheat plants under both well-watered and water-deficit conditions, potentially related to the water-deficit resilience. Collectively, our findings support that the ectopic AlSAP expression in durum wheat lines enhances water-deficit resilience ability, thereby potentially compensate for the GY loss in arid and semi-arid regions.

The newly assembled chloroplast genome of Aeluropus littoralis: molecular feature characterization and phylogenetic analysis with related species

Aeluropus littoralis, a halophyte grass, is widely distributed from the Mediterranean to the Indian subcontinent through the Mongolian Gobi. This model halophyte has garnered increasing attention owing to its use as forage and its high tolerance to environmental stressors. The chloroplast genomes of many plants have been extensively examined for molecular, phylogenetic and transplastomic applications. However, no published research on the A. littoralis chloroplast (cp) genome was discovered. Here, the entire chloroplast genome of A. littoralis was assembled implementing accurate long-read sequences. The entire chloroplast genome, with an estimated length of 135,532 bp (GC content: 38.2%), has a quadripartite architecture and includes a pair of inverted repeat (IR) regions, IRa and IRb (21,012 bp each), separated by a large and a small single-copy regions (80,823 and 12,685 bp, respectively). The features of A. littoralis consist of 133 genes that synthesize 87 peptides, 38 transfer RNAs, and 8 ribosomal RNAs. Of these genes, 86 were unique, whereas 19 were duplicated in IR regions. Additionally, a total of forty-six simple sequence repeats, categorized into 32-mono, four-di, two-tri, and eight-tetranucleotides, were discovered. Furthermore, ten sets of repeats greater than 20 bp were located primarily in the LSC region. Evolutionary analysis based on chloroplast sequence data revealed that A. littoralis with A. lagopoides and A. sinensis belong to the Aeluropodinae subtribe, which is a sister to the Eleusininae in the tribe Cynodonteae and the subfamily Chloridoideae. This subfamily belongs to the PACMAD clade, which contains the majority of the C4 photosynthetic plants in the Poaceae. The newly constructed A. littoralis cp genome offers valuable knowledge for DNA barcoding, phylogenetic, transplastomic research, and other biological studies.

Functional Characterization of Lobularia maritima LmTrxh2 Gene Involved in Cold Tolerance in Tobacco through Alleviation of ROS Damage to the Plasma Membrane

Cold stress is a key environmental factor affecting plant growth and development, crop productivity, and geographic distribution. Thioredoxins (Trxs) are small proteins that are ubiquitously expressed in all organisms and implicated in several cellular processes, including redox reactions. However, their role in the regulation of cold stress in the halophyte plant Lobularia maritima remains unknown. We recently showed that overexpression of LmTrxh2, which is the gene that encodes the h-type Trx protein previously isolated from L. maritima, led to an enhanced tolerance to salt and osmotic stress in transgenic tobacco. This study functionally characterized the LmTrxh2 gene via its overexpression in tobacco and explored its cold tolerance mechanisms. Results of the RT-qPCR and western blot analyses indicated differential temporal and spatial regulation of LmTrxh2 in L. maritima under cold stress at 4 °C. LmTrxh2 overexpression enhanced the cold tolerance of transgenic tobacco, as evidenced by increased germination rate, fresh weight and catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) activities; reduced malondialdehyde levels, membrane leakage, superoxide anion (O₂^-), and hydrogen peroxide (H₂O₂) levels; and higher retention of chlorophyll than in non-transgenic plants (NT). Furthermore, the transcript levels of reactive oxygen species (ROS)-related genes (NtSOD and NtCAT1), stress-responsive late embryogenis abundant protein 5 (NtLEA5), early response to dehydration 10C (NtERD10C), DRE-binding proteins 1A (NtDREB1A), and cold-responsive (COR) genes (NtCOR15A, NtCOR47, and NtKIN1) were upregulated in transgenic lines compared with those in NT plants under cold stress, indicating that LmTrxh2 conferred cold stress tolerance by enhancing the ROS scavenging ability of plants, thus enabling them to maintain membrane integrity. These results suggest that LmTrxh2 promotes cold tolerance in tobacco and provide new insight into the improvement of cold-stress resistance to cold stress in non-halophyte plants and crops.

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.

Comprehensive Identification and Functional Analysis of Stress-Associated Protein (SAP) Genes in Osmotic Stress in Maize

Stress-associated proteins (SAPs) are a kind of zinc finger protein with an A20/AN1 domain and contribute to plants' adaption to various abiotic and biological stimuli. However, little is known about the SAP genes in maize (Zea mays L.). In the present study, the SAP genes were identified from the maize genome. Subsequently, the protein properties, gene structure and duplication, chromosomal location, and cis-acting elements were analyzed by bioinformatic methods. Finally, their expression profiles under osmotic stresses, including drought and salinity, as well as ABA, and overexpression in Saccharomyces cerevisiae W303a cells, were performed to uncover the potential function. The results showed that a total of 10 SAP genes were identified and named ZmSAP1 to ZmSAP10 in maize, which was unevenly distributed on six of the ten maize chromosomes. The ZmSAP1, ZmSAP4, ZmSAP5, ZmSAP6, ZmSAP7, ZmSAP8 and ZmSAP10 had an A20 domain at N terminus and AN1 domain at C terminus, respectively. Only ZmSAP2 possessed a single AN1 domain at the N terminus. ZmSAP3 and ZmSAP9 both contained two AN1 domains without an A20 domain. Most ZmSAP genes lost introns and had abundant stress- and hormone-responsive cis-elements in their promoter region. The results of quantitative real-time PCR showed that all ZmSAP genes were regulated by drought and saline stresses, as well as ABA induction. Moreover, heterologous expression of ZmSAP2 and ZmSAP7 significantly improved the saline tolerance of yeast cells. The study provides insights into further underlying the function of ZmSAPs in regulating stress response in maize.

Evaluation of Halophyte Biopotential as an Unused Natural Resource: The Case of Lobularia maritima

Halophytes are plant species widely distributed in saline habitats, such as beaches, postindustrial wastelands, irrigated lands, salt flats, and others. Excessive salt level, known to limit plant growth, is not harmful to halophytes, which have developed a variety of defense mechanisms allowing them to colonize harsh environments. Plants under stress are known to respond with several morpho-anatomical adaptations, but also to enhance the production of secondary metabolites to better cope with difficult conditions. Owing to these adaptations, halophytes are an interesting group of undemanding plants with a high potential for application in the food and pharmaceutical industries. Therefore, this review aims to present the characteristics of halophytes, describe changes in their gene expression, and discuss their synthesized metabolites of pharmacognostic and pharmacological significance. Lobularia maritima is characterized as a widely spread halophyte that has been shown to exhibit various pharmacological properties in vitro and in vivo. It is concluded that halophytes may become important sources of natural products for the treatment of various ailments and for supplementing the human diet with necessary non-nutrients and minerals. However, extensive studies are needed to deepen the knowledge of their biological potential in vivo, so that they can be introduced to the pharmaceutical and food industries.

Comparative transcriptome and metabolome analysis reveal key regulatory defense networks and genes involved in enhanced salt tolerance of Actinidia (kiwifruit)

The Actinidia (kiwifruit) is an emerging fruit plant that is severely affected by salt stress in northern China. Plants have evolved several signaling network mechanisms to cope with the detrimental effects of salt stress. To date, no reported work is available on metabolic and molecular mechanisms involved in kiwifruit salt tolerance. Therefore, the present study aims to decipher intricate adaptive responses of two contrasting salt tolerance kiwifruit species Actinidia valvata [ZMH (an important genotype), hereafter referred to as R] and Actinidia deliciosa ['Hayward' (an important green-fleshed cultivar), hereafter referred to as H] under 0.4% (w/w) salt stress for time courses of 0, 12, 24, and 72 hours (hereafter refered to as h) by combined transcriptome and metabolome analysis. Data revealed that kiwifruit displayed specific enrichment of differentially expressed genes (DEGs) under salt stress. Interestingly, roots of R plants showed a differential expression pattern for up-regulated genes. The KEGG pathway analysis revealed the enrichment of DEGs related to plant hormone signal transduction, glycine metabolism, serine and threonine metabolism, glutathione metabolism, and pyruvate metabolism in the roots of R under salt stress. The WGCNA resulted in the identification of five candidate genes related to glycine betaine (GB), pyruvate, total soluble sugars (TSS), and glutathione biosynthesis in kiwifruit. An integrated study of transcriptome and metabolome identified several genes encoding metabolites involved in pyruvate metabolism. Furthermore, several genes encoding transcription factors were mainly induced in R under salt stress. Functional validation results for overexpression of a candidate gene betaine aldehyde dehydrogenase (AvBADH, R_transcript_80484) from R showed significantly improved salt tolerance in Arabidopsis thaliana (hereafter referred to as At) and Actinidia chinensis ['Hongyang' (an important red-fleshed cultivar), hereafter referred to as Ac] transgenic plants than in WT plants. All in all, salt stress tolerance in kiwifruit roots is an intricate regulatory mechanism that consists of several genes encoding specific metabolites.

Bio-Stimulating Effect of Natural Polysaccharides from Lobularia maritima on Durum Wheat Seedlings: Improved Plant Growth, Salt Stress Tolerance by Modulating Biochemical Responses and Ion Homeostasis

Bioactivities of polysaccharides derived from halophyte plants have gained attention in recent years. The use of biostimulants in agriculture is an innovative method of dealing with environmental stressors affecting plant growth and development. Here, we investigated the use of natural polysaccharides derived from the halophyte plant Lobularia maritima (PSLm) as a biostimulant in durum wheat seedlings under salt stress. Treatment with polysaccharide extract (0.5, 1, and 2 mg/mL PSLm) stimulated in vitro wheat growth, including germination, shoot length, root length, and fresh weight. PSLm at 2 mg/mL provided tolerance to plants against NaCl stress with improved membrane stability and low electrolyte leakage, increased antioxidant activities (catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD)), enhanced leaf chlorophyll fluorescence, proline, and total sugar contents, decreased lipid peroxidation (MDA), and reactive oxygen species (H₂O₂) levels, and coordinated the efflux and compartmentation of intracellular ions. The expression profile analyses of ten stress-related genes (NHX1, HKT1.4, SOS1, SOD, CAT, GA20-ox1, GA3-ox1, NRT1.1, NRT2.1, and GS) using RT-qPCR revealed the induction of several key genes in durum wheat growing in media supplemented with PSLm extract, even in unstressed conditions that could be related to the observed tolerance. This study revealed that PSLm extract contributes to salt tolerance in durum wheat seedlings, thereby enhancing their reactive oxygen species scavenging ability, and provided evidence for exploring PSLm as a plant biostimulant for sustainable and organic agriculture.

Initial Description of the Genome of Aeluropus littoralis, a Halophile Grass

The use of wild plant species or their halophytic relatives has been considered in plant breeding programs to improve salt and drought tolerance in crop plants. Aeluropus littoralis serves as halophyte model for identification and isolation of novel stress adaptation genes. A. littoralis, a perennial monocot grass, grows in damp or arid areas, often salt-impregnated places and wasteland in cultivated areas, can survive periodically high water salinity, and tolerate high salt concentrations in the soil up to 1,100 mM sodium chloride. Therefore, it serves as valuable genetic resource to understand molecular mechanisms of stress-responses in monocots. The knowledge can potentially be used for improving tolerance to abiotic stresses in economically important crops. Several morphological, anatomical, ecological, and physiological traits of A. littoralis have been investigated so far. After watering with salt water the grass is able to excrete salt via its salt glands. Meanwhile, a number of ESTs (expressed sequence tag), genes and promoters induced by the salt and drought stresses were isolated, sequenced and annotated at a molecular level. Transfer of stress related genes to other species resulted in enhanced stress resistance. Here we describe the genome sequence and structure of A. littoralis analyzed by whole genome sequencing and histological analysis. The chromosome number was determined to be 20 (2n = 2x = 20). The genome size was calculated to be 354 Mb. This genomic information provided here, will support the functional investigation and application of novel genes improving salt stress resistance in crop plants. The utility of the sequence information is exemplified by the analysis of the DREB-transcription factor family.

The E3 Ligase GmPUB21 Negatively Regulates Drought and Salinity Stress Response in Soybean

E3-ubiquitin ligases are known to confer abiotic stress responses in plants. In the present study, GmPUB21, a novel U-box E3-ubiquitin ligase-encoding gene, was isolated from soybean and functionally characterized. The expression of GmPUB21, which possesses E3-ubiquitin ligase activity, was found to be significantly up-regulated by drought, salinity, and ABA treatments. The fusion protein GmPUB21-GFP was localized in the cytoplasm, nucleus, and plasma membrane. Transgenic lines of the Nicotiana benthamiana over-expressing GmPUB21 showed more sensitive to osmotic, salinity stress and ABA in seed germination and inhibited mannitol/NaCl-mediated stomatal closure. Moreover, higher reactive oxygen species accumulation was observed in GmPUB21 overexpressing plants after drought and salinity treatment than in wild-type (WT) plants. Contrarily, silencing of GmPUB21 in soybean plants significantly enhanced the tolerance to drought and salinity stresses. Collectively, our results revealed that GmPUB21 negatively regulates the drought and salinity tolerance by increasing the stomatal density and aperture via the ABA signaling pathway. These findings improved our understanding of the role of GmPUB21 under drought and salinity stresses in soybean.

Ion content, antioxidant enzyme activity and transcriptional response under salt stress and recovery condition in the halophyte grass Aeluropus littoralis

OBJECTIVE

In contrast to glycophytes, halophyte plants have evolved unique morphological and physiological mechanisms to deal with abiotic stress. This study presents the physiological responses of Aeluropus littoralis, a halophyte grass, to salt stress and recovery conditions on the molecular level.

RESULTS

Elemental analysis showed that Na+ concentration increased in the analyzed tissue during salt stress application, and declined at recovery condition. With the exception of root tissue, comparable trends of K+, Ca2+, and Mg2+ concentrations were observed (decreased during salt stress, increased during recovery). Salinity led to an increase in total chlorophyll (Chl), Chl a, and carotenoids content, while Chl b content decreased. The level of the proline amino acid associated with drought and salt stress was increased. Here APX, POD, and SOD activity were strongly detectable in roots and reduced later under recovery conditions. RT-qPCR revealed up-regulation of antioxidant genes at S1 and S3 in the root but down-regulation in recovery conditions. This study found a significant halophyte index for understanding the processes of salinity tolerance in A. littoralis. These findings may provide insight into the role of antioxidant enzymes during salt stress and the mechanism underlying the plant's response to stress.

Zinc Oxide Nanoparticles and Their Biosynthesis: Overview

Zinc (Zn) is plant micronutrient, which is involved in many physiological functions, and an inadequate supply will reduce crop yields. Its deficiency is the widest spread micronutrient deficiency problem; almost all crops and calcareous, sandy soils, as well as peat soils and soils with high phosphorus and silicon content are expected to be deficient. In addition, Zn is essential for growth in animals, human beings, and plants; it is vital to crop nutrition as it is required in various enzymatic reactions, metabolic processes, and oxidation reduction reactions. Finally, there is a lot of attention on the Zn nanoparticles (NPs) due to our understanding of different forms of Zn, as well as its uptake and integration in the plants, which could be the primary step toward the larger use of NPs of Zn in agriculture. Nanotechnology application in agriculture has been increasing over recent years and constitutes a valuable tool in reaching the goal of sustainable food production worldwide. A wide array of nanomaterials has been used to develop strategies of delivery of bioactive compounds aimed at boosting the production and protection of crops. ZnO-NPs, a multifunctional material with distinct properties and their doped counterparts, were widely being studied in different fields of science. However, its application in environmental waste treatment and many other managements, such as remediation, is starting to gain attention due to its low cost and high productivity. Nano-agrochemicals are a combination of nanotechnology with agrochemicals that have resulted in nano-fertilizers, nano-herbicides, nano-fungicides, nano-pesticides, and nano-insecticides being developed. They have anti-bacterial, anti-fungal, anti-inflammatory, antioxidant, and optical capabilities. Green approaches using plants, fungi, bacteria, and algae have been implemented due to the high rate of harmful chemicals and severe situations used in the manufacturing of the NPs. This review summarizes the data on Zn interaction with plants and contributes towards the knowledge of Zn NPs and its impact on plants.

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.

Negative impact of long-term exposure of salinity and drought stress on native Tetraena mandavillei L

Tetraena mandavillei L. is a perennial shrub native to the Middle Eastern countries of Asia, which is extensively regarded as a drought-tolerant plant. However, the plant reduces growth and biomass when grown in high concentrations of sodium chloride in the soil. We conducted a pot experiment to influence the negative impact of different levels of salinity (0, 10, and 20 dSm^-1 ) and drought stress (100, 80, 60, and 40% water field capacity), to study different growth-related parameters, physiological alterations and ion uptake by T. mandavillei. Both salinity and drought stress caused a negative impact by affecting several attributes of T. mandavillei, but the plants showed some resistance against drought stress conditions in terms of growth and biomass. In addition to that, we noticed that a combinatorial and individual impact of drought and salinity stress decreased photosynthetic pigments and gas exchange parameters in T. mandavillei. Results also depicted that the combination of the abiotic stress conditions drought and salinity induced reactive oxygen species (ROS), indicating that the plants undergo oxidative damaged. However, due to the active plant defense system, the plant enhanced its performance under abiotic stress conditions, but due to the severe drought condition (40% water field capacity), a significant (P < 0.05) decrease in the activities of antioxidant compounds was caused. Furthermore, osmolytes also increased under both salinity and drought stress conditions in this study. Our results also showed that increased salinity and drought stress in the soil caused a significant increase in sodium (Na⁺ ) and chloride (Cl^- ) ions in roots and shoots of T. mandavillei. In contrast to that, the contents of Calcium (Ca²⁺ ) and potassium (K⁺ ) were decreased in all organs of the plants with increasing levels of salinity and drought stress. Taken together, T. mandavillei can be classified as a facultative halophyte with the ability to tolerate drought stress and using salt accumulation mechanisms to tolerate salinity stress.

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.

Loci harboring genes with important role in drought and related abiotic stress responses in flax revealed by multiple GWAS models

QTNs associated with drought tolerance traits and indices were identified in a flax mini-core collection through multiple GWAS models and phenotyping at multiple locations under irrigated and non-irrigated field conditions. Drought is a critical phenomenon challenging today's agricultural sector. Crop varieties adapted to moisture deficit are becoming vital. Flax can be greatly affected by limiting moisture conditions, especially during the early development and reproductive stages. Here, a mini-core collection comprising genotypes from more than 20 major growing countries was evaluated for 11 drought-related traits in irrigated and non-irrigated fields for 3 years. Heritability of the traits ranged from 44.7 to 86%. Six of the 11 traits showed significant phenotypic difference between irrigated and non-irrigated conditions. A genome-wide association study (GWAS) was performed for these six traits and their corresponding stress indices based on 106 genotypes and 12,316 single nucleotide polymorphisms (SNPs) using six multi-locus and one single-locus models. The SNPs were then assigned to 8050 linkage disequilibrium (LD) blocks to which a restricted two-stage multi-locus multi-allele GWAS was applied. A total of 144 quantitative trait nucleotides (QTNs) and 13 LD blocks were associated with at least one trait or stress index. Of these, 16 explained more than 15% of the genetic variance. Most large-effect QTN loci harbored gene(s) previously predicted to play role(s) in the associated traits. Genes mediating responses to abiotic stresses resided at loci associated with stress indices. Flax genes Lus10009480 and Lus10030150 that are predicted to encode WAX INDUCER1 and STRESS-ASSOCIATED PROTEIN (SAP), respectively, are among the important candidates detected. Accessions with multiple favorable alleles outperformed others for grain yield, thousand seed weight and fiber/biomass in non-irrigated conditions, suggesting their potential usefulness in breeding and genomic selection.

Identification and characterization of differentially expressed genes in the rice root following exogenous application of spermidine during salt stress

Salinity is a major limiting factor in crop production. Exogenous spermidine (spd) effectively ameliorates salt injury, though the underlying molecular mechanism is poorly understood. We have used a suppression subtractive hybridization method to construct a cDNA library that has identified up-regulated genes from rice root under the treatment of spd and salt. Total 175 high-quality ESTs of about 100-500 bp in length with an average size of 200 bp are isolated, clustered and assembled into a collection of 62 unigenes. Gene ontology analysis using the KEGG pathway annotation database has classified the unigenes into 5 main functional categories and 13 subcategories. The transcripts abundance has been validated using Real-Time PCR. We have observed seven different types of post-translational modifications in the DEPs. 44 transmembrane helixes are predicted in 6 DEPs. This above information can be used as first-hand data for dissecting the administrative role of spd during salinity.

Overexpression of wheat α-mannosidase gene TaMP impairs salt tolerance in transgenic Brachypodium distachyon

The TaMP gene from wheat encodes an α-mannosidase induced by salt stress that functions as negative regulator of salt tolerance in plants. Salt stress significantly affects growth and yield of crop plants. The α-mannosidases function in protein folding, trafficking, and endoplasmic reticulum-associated degradation in eukaryotic cells, and they are involved in abiotic stress tolerance in plants. Previously, we identified the α-mannosidase gene TaMP in wheat (Triticum aestivum). In this study, we investigated the function of TaMP in salt stress tolerance. TaMP expression was induced in wheat leaves by salt, drought, abscisic acid, and H₂O₂ treatments. Overexpressing TaMP in Brachypodium distachyon was associated with a salt-sensitive phenotype. Under salt stress, the overexpressing plants had reduced height, delayed growth status, low photosynthetic rate, decreased survival rate, and diminished yield. Moreover, the overexpression of TaMP aggravated the tendency for ions to become toxic under salt stress by significantly affecting the Na⁺ and K⁺ contents in cells. In addition, TaMP could negatively regulate salt tolerance by affecting the antioxidant enzyme system capacity and increasing the reactive oxygen species accumulation. Our study was helpful to understand the underlying physiological and molecular mechanisms of salt stress tolerance in plants.

Identification and Expression Analysis of Stress-Associated Proteins (SAPs) Containing A20/AN1 Zinc Finger in Cucumber

Stress-associated proteins (SAPs) are a class of zinc finger proteins that confer tolerance to a variety of abiotic and biotic stresses in diverse plant species. However, in cucumber (Cucumis sativus L.), very little is known about the roles of SAP gene family members in regulating plant growth, development, and stress responses. In this study, a total of 12 SAP genes (named as CsSAP1-CsSAP12) were identified in the cucumber genome, which were unevenly distributed on six chromosomes. Gene duplication analysis detected one tandem duplication and two segmental duplication events. Phylogenetic analysis of SAP proteins from cucumber and other plants suggested that they could be divided into seven groups (sub-families), and proteins in the same group generally had the same arrangement of AN1 (ZnF-AN1) and A20 (ZnF-A20) domains. Most of the CsSAP genes were intronless and harbored a number of stress- and hormone-responsive cis-elements in their promoter regions. Tissue expression analysis showed that the CsSAP genes had a broad spectrum of expression in different tissues, and some of them displayed remarkable alteration in expression during fruit development. RT-qPCR results indicated that all the selected CsSAP genes displayed transcriptional responses to cold, drought, and salt stresses. These results enable the first comprehensive description of the SAP gene family in cucumber and lay a solid foundation for future research on the biological functions of CsSAP genes.

Root Response to Drought Stress in Rice (Oryza sativa L.)

The current unpredictable climate changes are causing frequent and severe droughts. Such circumstances emphasize the need to understand the response of plants to drought stress, especially in rice, one of the most important grain crops. Knowledge of the drought stress response components is especially important in plant roots, the major organ for the absorption of water and nutrients from the soil. Thus, this article reviews the root response to drought stress in rice. It is presented to provide readers with information of use for their own research and breeding program for tolerance to drought stress in rice.

Functional domain analysis of LmSAP protein reveals the crucial role of the zinc-finger A20 domain in abiotic stress tolerance

Stress-associated proteins (SAPs), such as A20/AN1 zinc-finger domain-containing proteins, have emerged as a novel class of proteins involved in abiotic stress signaling, and they are important candidates for preventing the loss of yield caused by exposure to environmental stresses. In a previous report, it was found that the ectopic-expression of Lobularia maritima stress-associated protein, LmSAP, conferred tolerance to abiotic and heavy metal stresses in transgenic tobacco plants. This study aimed to investigate the functions of the A20 and AN1 domains of LmSAP in salt and osmotic stress tolerance. To this end, in addition to the full-length LmSAP gene, we have generated three LmSAP-truncated forms (LmSAPΔA20, LmSAPΔAN1, and LmSAPΔA20-ΔAN1). Heterologous expression in Saccharomyces cerevisiae of different truncated forms of LmSAP revealed that the A20 domain is essential to increase cell tolerance to salt, ionic, and osmotic stresses. Transgenic tobacco plants overexpressing LmSAP and LmSAPΔAN1 constructs exhibited higher tolerance to salt and osmotic stresses in comparison to the non-transgenic plants (NT) and lines transformed with LmSAPΔA20 and LmSAPΔA20-ΔAN1 constructs. Similarly, transgenic plants overexpressing the full-length LmSAP gene and LmSAPΔAN1 truncated domain maintained higher superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) enzymatic activities due to the high expression levels of the genes encoding these key antioxidant enzymes, MnSOD, POD, and CAT1, as well as accumulated lower levels of malondialdehyde (MDA) under salt and osmotic stresses compared to NT and LmSAPΔA20 and LmSAPΔA20-ΔAN1 forms. These findings provide insights into the pivotal role of A20 and AN1 domains of LmSAP protein in salt and osmotic stress tolerance.

Exploiting Differential Gene Expression to Discover Ionic and Osmotic-Associated Transcripts in the Halophyte Grass Aeluropus littoralis

BACKGROUND

Salinity as a most significant environmental challenges affects the growth and productivity of plants worldwide. In this study, the ionic and iso-osmotic effects of salt stress were investigated in Aeluropus littoralis L., a halophyte grass species from Poaceae family, by cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique. To dissect the two different effects (ionic and osmotic) exerted by salt stress, various ionic agents including 200 and 400 mM sodium chloride (NaCl), 200 and 400 mM potassium chloride (KCl) as well as 280 and 406 gl- 1 (- 0.9 and - 1.4 MPa) polyethylene glycol 6000 (PEG) as their iso-osmotic concentrations were applied.

RESULTS

Application of KCl and PEG significantly reduced the fresh weight (FW) of A. littoralis seedlings compared to control while NaCl treatment markedly enhanced the FW. At the transcriptome level, different observations of changes in gene expression have been made in response of A. littoralis to ionic and osmotic stresses. Out of 69 transcript derived fragments (TDFs), 42 TDFs belong to 9 different groups of genes involved in metabolism (11.6%), transcription (10.2%), ribosomal protein (8.7%), protein binding (8.7%) transporter (5.8%), translation (5.8%), signal transduction (4.3%), nucleosome assembly protein (2.9%) and catabolism (2.9%). The 44 and 28 percent of transcripts were expressed under ionic stress (NaCl-specific and KCl-specific) and osmotic stress (common with NaCl, KCl and PEG), respectively which indicating a greater response of plants to ionic stress than osmotic stress. Expression pattern of eight candidate TDFs including; SYP81, CAND1, KATN, ISB1, SAMDC, GLY1, HAK18 and ZF30 was evaluated by RT-qPCR at high salinity levels and recovery condition.

CONCLUSION

Differential regulation of these TDFs was observed in root and shoot which confirm their role in salt stress tolerance and provide initial insights into the transcriptome of A. littoralis. Expression pattern of ionic and osmotic-related TDFs at A. littoralis can be taken as an indication of their functional relevance at different salt and drought stresses.

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.

Transcriptome and metabolome analyses of two contrasting sesame genotypes reveal the crucial biological pathways involved in rapid adaptive response to salt stress

BACKGROUND

Soil salinity is one of the major serious factors that affect agricultural productivity of almost all crops worldwide, including the important oilseed crop sesame. In order to improve salinity resistance in sesame, it is crucial to understand the molecular mechanisms underlying the adaptive response to salinity stress.

RESULTS

In the present study, two contrasting sesame genotypes differing in salt tolerance were used to decipher the adaptive responses to salt stress based on morphological, transcriptome and metabolome characterizations. Morphological results indicated that under salt stress, the salt-tolerant (ST) genotype has enhanced capacity to withstand salinity stress, higher seed germination rate and plant survival rate, as well as better growth rate than the salt-sensitive genotype. Transcriptome analysis revealed strongly induced salt-responsive genes in sesame mainly related to amino acid metabolism, carbohydrate metabolism, biosynthesis of secondary metabolites, plant hormone signal transduction, and oxidation-reduction process. Especially, several pathways were preferably enriched with differentially expressed genes in ST genotype, including alanine, aspartate and glutamate metabolism, carotenoid biosynthesis, galactose metabolism, glycolysis/gluconeogenesis, glyoxylate and dicarboxylate metabolism, porphyrin and chlorophyll metabolism. Metabolome profiling under salt stress showed a higher accumulation degree of metabolites involved in stress tolerance in ST, and further highlighted that the amino acid metabolism, and sucrose and raffinose family oligosaccharides metabolism were enhanced in ST.

CONCLUSIONS

These findings suggest that the candidate genes and metabolites involved in crucial biological pathways may regulate salt tolerance of sesame, and increase our understanding of the molecular mechanisms underlying the adaptation of sesame to salt stress.

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.

Genome-Wide Analysis and Cloning of the Apple Stress-Associated Protein Gene Family Reveals MdSAP15, Which Confers Tolerance to Drought and Osmotic Stresses in Transgenic Arabidopsis

Stress-associated proteins (SAPs) are novel A20/AN1 zinc finger domain-containing proteins that are now favorable targets to improve abiotic stress tolerance in plants. However, the SAP gene family and their biological functions have not been identified in the important fruit crop apple (Malus × domestica Borkh.). We conducted a genome-wide analysis and cloning of this gene family in apple and determined that the overexpression of MdSAP15 enhances drought tolerance in Arabidopsis plants. We identified 30 SAP genes in the apple genome. Phylogenetic analysis revealed two major groups within that family. Results from sequence alignments and analyses of 3D structures, phylogenetics, genomics structure, and conserved domains indicated that apple SAPs are highly and structurally conserved. Comprehensive qRT-PCR analysis found various expression patterns for MdSAPs in different tissues and in response to a water deficit. A transgenic analysis showed that the overexpression of MdSAP15 in transgenic Arabidopsis plants markedly enhanced their tolerance to osmotic and drought stresses. Our results demonstrate that the SAP genes are highly conserved in plant species, and that MdSAP15 can be used as a target gene in genetic engineering approaches to improve drought tolerance.

Overexpression of AlTMP2 gene from the halophyte grass Aeluropus littoralis in transgenic tobacco enhances tolerance to different abiotic stresses by improving membrane stability and deregulating some stress-related genes

Herein, we report isolation of the AlTMP2 gene from the halophytic C4 grass Aeluropus littoralis. The subcellular localization suggested that AlTMP2 is a plasma membrane protein. In A. littoralis exposed to salt and osmotic stresses, the AlTMP2 gene was induced early and at a high rate, but was upregulated relatively later in response to abscisic acid and cold treatments. Expression of AlTMP2 in tobacco conferred improved tolerance against salinity, osmotic, H2O2, heat, and freezing stresses at the germination and seedling stages. Under control conditions, no growth or yield penalty were mentioned in transgenic plants due to the constitutive expression of AlTMP2. Interestingly, under greenhouse conditions, the seed yield of transgenic plants was significantly higher than that of non-transgenic (NT) plants grown under salt or drought stress. Furthermore, AlTMP2 plants had less electrolyte leakage, higher membrane stability, and lower Na+ and higher K+ accumulation than NT plants. Finally, six stress-related genes were shown to be deregulated in AlTMP2 plants relative to NT plants under both control and stress conditions. Collectively, these results indicate that AlTMP2 confers abiotic stress tolerance by improving ion homeostasis and membrane integrity, and by deregulating certain stress-related genes.

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.

The Phosphoproteomic Response of Rice Seedlings to Cadmium Stress

The environmental damage caused by cadmium (Cd) pollution is of increasing concern in China. While the overall plant response to Cd has been investigated in some depth, the contribution (if any) of protein phosphorylation to the detoxification of Cd and the expression of tolerance is uncertain. Here, the molecular basis of the plant response has been explored in hydroponically raised rice seedlings exposed to 10 μΜ and 100 μΜ Cd²⁺ stress. An analysis of the seedlings’ quantitative phosphoproteome identified 2454 phosphosites, associated with 1244 proteins. A total of 482 of these proteins became differentially phosphorylated as a result of exposure to Cd stress; the number of proteins affected in this way was six times greater in the 100 μΜ Cd²⁺ treatment than in the 10 μΜ treatment. A functional analysis of the differentially phosphorylated proteins implied that a significant number was involved in signaling, in stress tolerance and in the neutralization of reactive oxygen species, while there was also a marked representation of transcription factors.

Transcriptomic analysis to uncover genes affecting cold resistance in the Chinese honey bee (Apis cerana cerana)

The biological activity and geographical distribution of honey bees is strongly temperature-dependent, due to their ectothermic physiology. In China, the endemic Apis cerana cerana exhibits stronger cold hardiness than Western honey bees, making the former species important pollinators of winter-flowering plants. Although studies have examined behavioral and physiological mechanisms underlying cold resistance in bees, data are scarce regarding the exact molecular mechanisms. Here, we investigated gene expression in A. c. cerana under two temperature treatments, using transcriptomic analysis to identify differentially expressed genes (DEGs) and relevant biological processes, respectively. Across the temperature treatments, 501 DEGs were identified. A gene ontology analysis showed that DEGs were enriched in pathways related to sugar and amino acid biosynthesis and metabolism, as well as calcium ion channel activity. Additionally, heat shock proteins, zinc finger proteins, and serine/threonine-protein kinases were differentially expressed between the two treatments. The results of this study provide a general digital expression profile of thermoregulation genes responding to cold hardiness in A. c. cerana. Our data should prove valuable for future research on cold tolerance mechanisms in insects, and may be beneficial in breeding efforts to improve bee hardiness.

Expression of the Aeluropus littoralis AlSAP Gene Enhances Rice Yield under Field Drought at the Reproductive Stage

We evaluated the yields of Oryza sativa L. 'Nipponbare' rice lines expressing a gene encoding an A20/AN1 domain stress-associated protein, AlSAP, from the halophyte grass Aeluropus littoralis under the control of different promoters. Three independent field trials were conducted, with drought imposed at the reproductive stage. In all trials, the two transgenic lines, RN5 and RN6, consistently out-performed non-transgenic (NT) and wild-type (WT) controls, providing 50-90% increases in grain yield (GY). Enhancement of tillering and panicle fertility contributed to this improved GY under drought. In contrast with physiological records collected during previous greenhouse dry-down experiments, where drought was imposed at the early tillering stage, we did not observe significant differences in photosynthetic parameters, leaf water potential, or accumulation of antioxidants in flag leaves of AlSAP-lines subjected to drought at flowering. However, AlSAP expression alleviated leaf rolling and leaf drying induced by drought, resulting in increased accumulation of green biomass. Therefore, the observed enhanced performance of the AlSAP-lines subjected to drought at the reproductive stage can be tentatively ascribed to a primed status of the transgenic plants, resulting from a higher accumulation of biomass during vegetative growth, allowing reserve remobilization and maintenance of productive tillering and grain filling. Under irrigated conditions, the overall performance of AlSAP-lines was comparable with, or even significantly better than, the NT and WT controls. Thus, AlSAP expression inflicted no penalty on rice yields under optimal growth conditions. Our results support the use of AlSAP transgenics to reduce rice GY losses under drought conditions.

Ectopic Expression of Aeluropus littoralis Plasma Membrane Protein Gene AlTMP1 Confers Abiotic Stress Tolerance in Transgenic Tobacco by Improving Water Status and Cation Homeostasis

We report here the isolation and functional analysis of AlTMP1 gene encoding a member of the PMP3 protein family. In Aeluropus littoralis, AlTMP1 is highly induced by abscisic acid (ABA), cold, salt, and osmotic stresses. Transgenic tobacco expressing AlTMP1 exhibited enhanced tolerance to salt, osmotic, H₂O₂, heat and freezing stresses at the seedling stage. Under greenhouse conditions, the transgenic plants showed a higher level of tolerance to drought than to salinity. Noteworthy, AlTMP1 plants yielded two- and five-fold more seeds than non-transgenic plants (NT) under salt and drought stresses, respectively. The leaves of AlTMP1 plants accumulated lower Na⁺ but higher K⁺ and Ca2+ than those of NT plants. Tolerance to osmotic and salt stresses was associated with higher membrane stability, low electrolyte leakage, and improved water status. Finally, accumulation of AlTMP1 in tobacco altered the regulation of some stress-related genes in either a positive (NHX1, CAT1, APX1, and DREB1A) or negative (HKT1 and KT1) manner that could be related to the observed tolerance. These results suggest that AlTMP1 confers stress tolerance in tobacco through maintenance of ion homeostasis, increased membrane integrity, and water status. The observed tolerance may be due to a direct or indirect effect of AlTMP1 on the expression of stress-related genes which could stimulate an adaptive potential not present in NT plants.

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.

Proteomic responses in shoots of the facultative halophyte Aeluropus littoralis (Poaceae) under NaCl salt stress

Salinity is an environmental constraint that limits agricultural productivity worldwide. Studies on the halophytes provide valuable information to describe the physiological and molecular mechanisms of salinity tolerance. Therefore, because of genetic relationships of Aeluropus littoralis (Willd) Parl. with rice, wheat and barley, the present study was conducted to investigate changes in shoot proteome patterns in response to different salt treatments using proteomic methods. To examine the effect of salinity on A. littoralis proteome pattern, salt treatments (0, 200 and 400mM NaCl) were applied for 24h and 7 and 30 days. After 24h and 7 days exposure to salt treatments, seedlings were fresh and green, but after 30 days, severe chlorosis was established in old leaves of 400mM NaCl-salt treated plants. Comparative proteomic analysis of the leaves revealed that the relative abundance of 95 and 120 proteins was significantly altered in 200 and 400mM NaCl treated plants respectively. Mass spectrometry-based identification was successful for 66 out of 98 selected protein spots. These proteins were mainly involved in carbohydrate, energy, amino acids and protein metabolisms, photosynthesis, detoxification, oxidative stress, translation, transcription and signal transduction. These results suggest that the reduction of proteins related to photosynthesis and induction of proteins involved in glycolysis, tricarboxylic acid (TCA) cycle, and energy metabolism could be the main mechanisms for salt tolerance in A. littoralis. This study provides important information about salt tolerance, and a framework for further functional studies on the identified proteins in A. littoralis.

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.

Identification and validation of Aeluropus littoralis reference genes for Quantitative Real-Time PCR Normalization

Background

The use of stably expressed genes as normalizers has crucial role in accurate and reliable expression analysis estimated by quantitative real-time polymerase chain reaction (qPCR). Recent studies have shown that, the expression levels of common housekeeping genes are varying in different tissues and experimental conditions. The genomic DNA contamination in RNA samples is another important factor that also influence the interpretation of the data obtained from qPCR. It is estimated that the gDNA contamination in gene expression analysis lead to an overestimation of the RNA transcript level. The aim of this study was to validate the most stably expressed reference genes in two different tissues of Aeluropus littoralis—halophyte grass at salt stress and recovery condition. Also, a qPCR-based approach for monitoring contamination with gDNA was conducted.

Results

Ten candidate reference genes participating in different biological processes were analyzed in four groups of samples including root and leaf tissues, salt stress and recovery condition. To determine the most stably expressed reference genes, three statistical methods (geNorm, NormFinder and BestKeeper) were applied. According to results obtained, ten candidate reference genes were ranked based on the stability of their expression. Here, our results show that a set of four housekeeping genes (HKGs) e.g. RPS3, EF1A, GTF and RPS12 could be used as general reference genes for the all selected conditions and tissues. Also, four set of reference genes were proposed for each tissue and condition including: RPS3, EF1A and UBQ for salt stress and root samples; RPS3, EF1A, UBQ as well as GAPDH for recovery condition; U2SURP and GTF for leaf samples. Additionally, for assessing DNA contamination in RNA samples, a set of unique primers were designed based on the conserved region of ribosomal DNA (rDNA). The universality, specificity and sensitivity of these primer pairs were also evaluated in Poaceae.

Conclusions

Overall, the sets of reference genes proposed in this study are ideal normalizers for qPCR analysis in A.littoralis transcriptome. The novel reference gene e.g. RPS3 that applied this study had higher expression stability than commonly used housekeeping genes. The application of rDNA-based primers in qPCR analysis was addressed.

Electronic supplementary material

The online version of this article (doi:10.1186/s40709-016-0053-8) contains supplementary material, which is available to authorized users.

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.

Insights into the physiological responses of the facultative halophyte Aeluropus littoralis to the combined effects of salinity and phosphorus availability

In this work, we investigate the physiological responses to P deficiency (5μM KH2PO4=D), salt stress (400mM NaCl=C+S), and their combination (D+S) on the facultative halophyte Aeluropus littoralis to understand how plants adapt to these combined stresses. When individually applied, both P deficiency and salinity significantly restricted whole plant growth, with a more marked effect of the latter stress. However, the effects of the two stresses were not additive in plant biomass production since the response of plants to combined salinity and P deficiency was similar to that of plants grown under salt stress alone. In addition the observed features under salinity alone are kept when plants are simultaneously subjected to the combined effects of salinity and P deficiency such as biomass partitioning; the synthesis of proline and the K(+)/Na(+) selectivity ratio. Thus, increasing P availability under saline conditions has no significant effect on salt tolerance in this species. Plants cultivated under the combined effects of salinity and P deficiency exhibited the lowest leaf water potential. This trend was associated with a high accumulation of Na(+), Cl(-) and proline in shoots of salt treated plants suggesting the involvement of these solutes in osmotic adjustment. Proline could be involved in other physiological processes such as free radical scavenging. Furthermore, salinity has no significant effect on phosphorus acquisition when combined with a low P supply and it significantly decreased this parameter when combined with a sufficient P supply. This fact was probably due to salt's effect on P transporters. In addition, shoot soluble sugars accumulation under both P deficiency treatments with and without salt likely play an important role in the adaptation of A. littoralis plants to P shortage applied alone or combined with salinity. Moreover, there was a strong correlation between shoot and root intracellular acid phosphatase activity and phosphorus use efficiency which strengthens the assumption that intracellular acid phosphatase enzymes are involved in P remobilization in this species. Finally, our results showed that P availability has no significant effect on salt excretion in A. littorlais which suggests that independently of the P status in the plant, excretion remains priority over other functions requiring energy such as growth. This result could also indicate that salt excretion is not energy-dependent in this species.

Physiological and proteomic analyses of salt stress response in the halophyte Halogeton glomeratus

Very little is known about the adaptation mechanism of Chenopodiaceae Halogeton glomeratus, a succulent annual halophyte, under saline conditions. In this study, we investigated the morphological and physiological adaptation mechanisms of seedlings exposed to different concentrations of NaCl treatment for 21 d. Our results revealed that H. glomeratus has a robust ability to tolerate salt; its optimal growth occurs under approximately 100 mm NaCl conditions. Salt crystals were deposited in water-storage tissue under saline conditions. We speculate that osmotic adjustment may be the primary mechanism of salt tolerance in H. glomeratus, which transports toxic ions such as sodium into specific salt-storage cells and compartmentalizes them in large vacuoles to maintain the water content of tissues and the succulence of the leaves. To investigate the molecular response mechanisms to salt stress in H. glomeratus, we conducted a comparative proteomic analysis of seedling leaves that had been exposed to 200 mm NaCl for 24 h, 72 h and 7 d. Forty-nine protein spots, exhibiting significant changes in abundance after stress, were identified using matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF MS/MS) and similarity searches across EST database of H. glomeratus. These stress-responsive proteins were categorized into nine functional groups, such as photosynthesis, carbohydrate and energy metabolism, and stress and defence response.

Transcriptome profiling and identification of transcription factors in ramie (Boehmeria nivea L. Gaud) in response to PEG treatment, using illumina paired-end sequencing technology

Ramie (Boehmeria nivea L. Gaud), commonly known as China grass, is a perennial bast fiber plant of the Urticaceae. In China, ramie farming, industry, and trade provide income for about five million people. Drought stress severely affects ramie stem growth and causes a dramatic decrease in ramie fiber production. There is a need to enhance ramie’s tolerance to drought stress. However, the drought stress regulatory mechanism in ramie remains unknown. Water stress imposed by polyethylene glycol (PEG) is a common and convenient method to evaluate plant drought tolerance. In this study, transcriptome analysis of cDNA collections from ramie subjected to PEG treatment was conducted using Illumina paired-end sequencing, which generated 170 million raw sequence reads. Between leaves and roots subjected to 24 (L2 and R2) and 72 (L3 and R3) h of PEG treatment, 16,798 genes were differentially expressed (9281 in leaves and 8627 in roots). Among these, 25 transcription factors (TFs) from the AP2 (3), MYB (6), NAC (9), zinc finger (5), and bZIP (2) families were considered to be associated with drought stress. The identified TFs could be used to further investigate drought adaptation in ramie.

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.

Salt tolerance mechanisms in Salt Tolerant Grasses (STGs) and their prospects in cereal crop improvement

Increasing soil salinity in the agricultural fields all over the world is a matter of concern. Salinity poses a serious threat to the normal growth and development of crop plants. What adds to the concern is that all the cereal crops are sensitive to increasing soil salinity. So it is implacable to either search for salinity resistant varieties of crop plants or transform them genetically to sustain growth and reproducibility at increasing salinity stress. For the second perspective, mining the salt tolerant genes in the close relatives of cereal crops apparently becomes important, and most specifically in the salt tolerant grasses (STGs). STGs include the halophytes, facultative halophytes and salt-tolerant glycophytes of the family Poaceae. In this review the potentiality of STGs has been evaluated for increasing the salinity tolerance of cereal crops. STGs are capable of surviving at increasing salt stress by utilizing different mechanisms that include vacuolization of toxic Na+ and Cl- in mature or senescing leaves, secretion of excess salts by salt glands, accumulation of osmolytes like proline and glycine betaine, and scavenging of ROS by antioxidative enzymes. The STGs are a therefore a potent source of salt tolerant genes.

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.

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.

Rice SAPs are responsive to multiple biotic stresses and overexpression of OsSAP1, an A20/AN1 zinc-finger protein, enhances the basal resistance against pathogen infection in tobacco

Eukaryotic A20/AN1 zinc-finger proteins (ZFPs) play an important role in the regulation of immune and stress response. After elucidation of the role of first such protein, OsSAP1, in abiotic stress tolerance, 18 rice stress associated protein (SAP) genes have been shown to be regulated by multiple abiotic stresses. In the present study, expression pattern of all the 18 OsSAP genes have been analysed in response to different biotic stress simulators, in order to get insights into their possible involvement in biotic stress tolerance. Our results showed the upregulation of OsSAP1 and OsSAP11 by all biotic stress simulator treatments. Furthermore, the functional role of OsSAP1 in plant defence responses has been explored through overexpression in transgenic plants. Constitutive expression of OsSAP1 in transgenic tobacco resulted into enhanced disease resistance against virulent bacterial pathogen, together with the upregulation of known defence-related genes. Present investigation suggests that rice SAPs are responsive to multiple biotic stresses and OsSAP1 plays a key role in basal resistance against pathogen infection. This strongly supports the involvement of rice SAPs in cross-talk between biotic and abiotic stress signalling pathways, which makes them ideal candidate to design strategies for protecting crop plants against multiple stresses.

Phosphoproteome analysis reveals new drought response and defense mechanisms of seedling leaves in bread wheat (Triticum aestivum L.)

Drought is a major form of abiotic stress that significantly affects plant growth and development. In this study, we performed the first phosphoproteome analysis of seedling leaves from two bread wheat cultivars (Hanxuan 10 and Ningchun 47) subjected to drought stress. As a result, a total of 191 and 251 unique phosphopeptides, representing 173 and 227 phosphoproteins in two cultivars, respectively, were identified as being significant changes in phosphorylation level (SCPL) under drought stress. Through the comparison of SCPL phosphoproteins between two cultivars, 31 common SCPL phosphoproteins were found in both cultivars. Function analysis showed that the SCPL phosphoproteins in the two cultivars are mainly involved in three biological processes: RNA transcription/processing, stress/detoxification/defense, and signal transduction. Further analyses revealed that some SCPL phosphoproteins may play key roles in signal transduction and the signaling cascade under drought stress. Furthermore, some phosphoproteins related to drought tolerance and osmotic regulation exhibited significant phosphorylation changes. This study used a series of bioinformatics tools to profile the phosphorylation status of wheat seedling leaves under drought stress with greater accuracy.

BIOLOGICAL SIGNIFICANCE

Drought is of the most studied abiotic stresses, because it severely restricts the development and yield of plants. In this study, large numbers of stress-related phosphoproteins are identified from the two bread wheat cultivars. These phosphoproteins contribute to signal transduction, osmotic regulation and ROS scavenging under water stress. This work provides a detailed insight into the mechanisms of drought response and defense in bread wheat from the perspective of phosphoproteomics, and identifies some important drought-tolerant candidates for further transgenosis study and incorporation into the breeding of resistant cultivars.