Genome-wide analysis of the stress associated protein (SAP) gene family containing A20/AN1 zinc-finger(s) in rice and their phylogenetic relationship with Arabidopsis

Heterologous overexpression of the Suaeda glauca stress-associated protein (SAP) family genes enhanced salt tolerance in Arabidopsis transgenic lines

Stress-associated proteins (SAPs), characterized by zinc finger domains, play a crucial role in regulating plant responses to various stresses. These proteins modulate stress-related gene expression and are integral to enhancing plant immunity, development, cell proliferation, and hormone regulation. In this study, we conducted a genome-wide analysis of the SAP gene family in Suaeda glauca (S. glauca), identifying 15 SAP genes encoding A20/AN1 zinc finger proteins. Functional analyses of three candidate genes under salinity stress were performed, examining phenotypic and physiological responses to better understand their role in stress tolerance. Sequence alignment, conserved domain analysis, and gene structure analysis revealed high conservation among S. glauca SAPs. Phylogenetic analysis identified two major groups within the gene family, providing insights into their evolutionary relationships. Transcription profiling analysis demonstrated significant expression of most SAP genes in response to salt stress, with qPCR validation confirming the upregulation of specific genes. Notably, transgenic Arabidopsis lines heterologously overexpressing the candidate genes SgSAP4, SgSAP5, and SgSAP7 demonstrated enhanced tolerance to salinity stress. This was evident from improved seed germination, root elongation, and reduced levels of stress markers, including malondialdehyde and free proline, compared to wild-type plants. These findings highlight the potential of these SAP genes in breeding programs aimed at improving salinity tolerance in crops.

De novo, high-quality assembly and annotation of the halophyte grass Aeluropus littoralis draft genome and identification of A20/AN1 zinc finger protein family

BACKGROUND

Aeluropus littoralis is considered a valuable natural forage plant for ruminant livestock and is highly tolerant to extreme abiotic stresses, especially salinity, drought, and heat. It is a monocotyledonous halophyte, has salt glands, performs C4-type photosynthesis and has a close genetic relationship with cereal crops. Moreover, previous studies have shown its huge potential as a reservoir of genes and promoters to understand and improve abiotic stress tolerance in crops.

RESULTS

The sequencing and hybrid assembly of the A. littoralis genome (2n = 2X = 20) using short and long reads from the BGISeq-500 and PacBio high-fidelity (HiFi) sequencing platforms, respectively. Using the k-mer analysis method, the haploid genome size of A. littoralis was estimated to be 360 Mb (with a heterozygosity rate of 1.88%). The hybrid assembled genome included 4,078 contigs with a GC content of 44% and covered 348 Mb. The longest contig and the N50 values were 5.1 Mb and 133.77 kb, respectively. The Benchmarking Universal Single Copy Ortholog (BUSCO) value was 91.1%, indicating good integrity of the assembled genome. The discovered repetitive elements accounted for 90.6 Mb, representing 26.03% of the total genome, and included a significant component of transposable elements (11.48%, ~40 Mb). Using a homology-based approach, 35,147 genes were predicted from the genome assembly. We next focused our analysis on the zinc-finger A20/AN1 gene family, a member of which (AlSAP) was previously shown to confer increased tolerance to osmotic and salt stresses when it was over-expressed in tobacco, wheat, and rice. Here, we identified the complete set of members of this family in the Aeluropus littoralis genome, thereby laying the foundation for their future functional analysis in cereal crops. In addition, the expression patterns of four novel genes from this family were analyzed by qPCR.

CONCLUSION

This resource and our findings will contribute to improve the current understanding of salinity tolerance in halophytes while providing useful genes and allelic variation to improve salinity and drought tolerance in cereals through genetic engineering and gene editing, respectively.

Comprehensive analysis of the stress associated protein (SAP) family and the function of PagSAP9 from Populus alba × P. glandulosa in salt stress

Poplar tree growth is frequently hindered by environmental stressors, particularly soil salinization. Enhancing salt tolerance is essential for improving their adaptability and biomass under these conditions. The Stress-Associated Protein (SAP) family, characterized by A20/AN1 zinc finger domains, plays a crucial role in plants' tolerance to abiotic stress. However, functional investigations on SAP proteins in poplar are limited. In our study, we identified 19 SAP members in poplar, distributed unevenly across ten chromosomes and classified them into two major groups based on phylogenetic relationship and structure characteristics. Notably, only three segmental duplications were found, while no tandem duplications were detected. The PagSAP9 gene from Populus alba x P. glandulosa, featured both A20 and AN1 domains, was successfully characterized and localized to both cytoplasm and nucleus. It was predominantly expressed in roots and leaves and showed significantly upregulation under salt stress. And the overexpressing PagSAP9 transgenic poplars enhanced the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), alongside reduced malondialdehyde (MDA) content. Additionally, DAB and NBT histological stainings further confirmed the positive effects of PagSAP9 gene. Collectively, these findings highlight the potential of the PagSAP9 gene to improve salt tolerance in poplar, emphasizing the broader applicability of SAP genes in plant stress resistance and providing valuable genetic resources for developing resilient plant varieties.

Unveiling the role of OsSAP17: Enhancing plant resistance to drought and salt

With the intensification of climate change coupled with the inadequate agricultural management in certain regions, plants face numerous challenges due to various abiotic stresses. Stress associated proteins (SAPs) are essential functional genes in plants for coping with stress. This research provides a functional analysis of OsSAP17, a protein belonging to the SAP family in rice. The expression level of OsSAP17 was induced under drought, salt stress and ABA treatment. Subcellular localization analysis revealed that the OsSAP17 protein was distributed in both the cytoplasm and nucleus. The ectopic expression of OsSAP17 significantly increased the capacity to withstand drought and salt stress in both transgenic yeast and Arabidopsis. Additionally, the ectopic expression of OsSAP17 led to notable changes in the expression of Arabidopsis ABA-related genes, including AtNCED3, AtABA2, and AtSnRK2.2. These results indicated that OsSAP17 was able to positively regulate drought and salt tolerance in plants. The insights from this study provided a fundamental understanding of the role of OsSAP17 in abiotic stress response mechanisms and were potentially valuable for breeding crops with enhanced stress tolerance.

Comparative transcriptome analysis and functional verification revealed that GhSAP6 negatively regulates salt tolerance in upland cotton

Owing to the scarcity of cultivable land in China, the agricultural sector is primarily focused on grain and oil crops. Simultaneously, the cultivation of cotton has gradually shifted towards regions characterized by elevated soil salinity levels. Additionally, the mechanism behind cotton's ability to tolerate salt remains elusive. In this study, we identified the Z9807 genotype as highly tolerant to salt stress, exhibiting superior leaf wilting resistance, antioxidant activity, catalase activity, K+/Na+ ratio, and growth compared to the salt-sensitive ZJ0102. Comparative transcriptome analysis revealed marked differences in salt stress responses between Z9807 and ZJ0102. This study identified a considerable number of differentially expressed genes associated with salt tolerance across multiple time points. By integration of QTL and GWAS mapping data, we successfully identified 621 candidate genes associated with salt tolerance. Weighted gene correlation network analysis exhibited three co-expression modules related to salt-tolerant Z9807 samples, ultimately identifying 15 core salt-tolerant candidate genes. We also conducted in-depth research on the salt tolerance of the stress-associated protein (SAP) GhSAP6 (GhSAP6_At and GhSAP6_Dt homologs). Results revealed that these candidate genes may inhibit salt tolerance through Virus-Induced Gene Silencing (VIGS) and transgenic overexpression assays conducted in Arabidopsis thaliana. Furthermore, we used yeast two-hybrid and luciferase assay experiments to confirm the ubiquitin degradation pathway between selected interacting proteins and verified the interaction with RAD23C. This study will provide new insights into the mechanisms related to salt tolerance in upland cotton.

NtSAP9 confers freezing tolerance in Nicotiana tabacum plants

Abiotic stresses, such as extreme temperatures, drought, and salinity, significantly affect plant growth and productivity. Among these, cold stress is particularly detrimental, impairing cellular processes and leading to reduced crop yields. In recent years, stress-associated proteins (SAPs) containing A20 and AN1 zinc-finger domains have emerged as crucial regulators in plant stress responses. However, the functions of SAPs in tobacco plants remain unclear. Here, we isolated Nicotiana tabacum SAP9 (NtSAP9), whose expression was induced by cold treatment, based on RNA-sequences data. Knock down of NtSAP9 expression reduced freezing tolerance, while overexpression conferred freezing tolerance in transgenic tobacco plants, as indicated by relative electrolytic leakage and photosystem II photochemical efficiency. Untargeted metabolomics via liquid chromatography-tandem mass spectrometry revealed distinct metabolic profiles between WT and NtSAP9-overexpressing tobacco plants under normal and low temperature conditions. Upregulation of amino acids like D-Glutamine, DL-Glutamine, and O-Acetyl-L-serine suggests NtSAP9 enhances cold tolerance. Further expression analysis by quantitative real-time PCR indicated that NtSAP9 participates in cold stress response possibly through amino acid synthesis-related genes expression, such as glutamine synthetase and glutamate dehydrogenase. These findings improve our understanding of SAP proteins in tobacco's response to cold stress.

Genome-wide identification of SAP family genes and characterization of TaSAP6-A1 to improve Cd tolerance in Triticum aestivum L

Stress Associated Proteins (SAPs) contain A20/AN1 zinc finger domains and, have been proposed to function in various physiological processes such as cold, salinity, drought, heavy metals, damage, and flooding resistance in plants. Here, a total of 131 SAP genes were identified, including T. aestivum (60), T. urartu (10), Ae. Tauschii (16), T. dicoccoides (13), O. sativa (18), and A. thaliana (14). A phylogenetic analysis revealed that the SAPs are clustered into two subfamilies. The TaSAP genes in the collinear region comprised 34 pairs of duplicated genes formed through segmental duplication events. Overexpressing TaSAP6-A1 in wheat enhanced Cd tolerance, whereas knock-down of this gene increased Cd sensitivity. Yeast two-hybrid (Y2H) and bimolecular fluorescent complementation assays (BiFC) demonstrated interaction between TaSAP6-A1 and phenylalanine ammonia-lyase (TaPAL), the first enzyme in the phenylpropanoid pathway. This study provides a valuable reference for further investigations into the functional and molecular mechanisms of the SAP gene family.

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.

SmJAZs-SmbHLH37/SmERF73-SmSAP4 module mediates jasmonic acid signaling to balance biosynthesis of medicinal metabolites and salt tolerance in Salvia miltiorrhiza

Salvia miltiorrhiza holds significant importance in traditional Chinese medicine. Stress-associated proteins (SAP), identified by A20/AN1 zinc finger structural domains, play crucial roles in regulating plant growth, development, resistance to biotic and abiotic stress, and hormone responses. Herein, we conducted a genome-wide identification of the SAP gene family in S. miltiorrhiza. The expression analysis revealed a significant upregulation of SmSAP4 under methyl jasmonate (MeJA) and salt stress. Overexpressing SmSAP4 in S. miltiorrhiza hairy roots increased tanshinones content while decreasing salvianolic acids content, while RNAi-silencing SmSAP4 had the opposite effect. SmSAP4 overexpression in both Arabidopsis thaliana and S. miltiorrhiza hairy roots decreased their salt stress tolerance, accompanied by increased activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and a hindered ability to maintain the Na+ : K+ ratio. Further investigations demonstrated that MeJA alleviated the inhibitory effect of SmJAZ3 on SmSAP4 activation by SmbHLH37 and SmERF73. However, MeJA did not affect the inhibition of SmSAP4 activation by SmJAZ8 through SmbHLH37. In summary, our research reveals that SmSAP4 negatively regulates the accumulation of salvianic acid through the SmJAZs-SmbHLH37/SmERF73-SmSAP4 module and positively impacting the accumulation of tanshinones. Additionally, it functions as a negative regulator under salt stress.

Pepper RING-Type E3 Ligase CaFIRF1 Negatively Regulates the Protein Stability of Pepper Stress-Associated Protein, CaSAP14, in the Dehydration Stress Response

As part of the cellular stress response in plants, the ubiquitin-proteasome system (UPS) plays a crucial role in regulating the protein stability of stress-related transcription factors. Previous study has indicated that CaSAP14 is functionally involved in enhancing pepper plant tolerance to dehydration stress by modulating the expression of downstream genes. However, the comprehensive regulatory mechanism underlying CaSAP14 remains incompletely understood. Here, we identified a RING-type E3 ligase, CaFIRF1, which interacts with and ubiquitinates CaSAP14. Pepper plants with silenced CaFIRF1 exhibited a dehydration-tolerant phenotype when subjected to dehydration stress, while overexpression of CaFIRF1 in pepper and Arabidopsis resulted in reduced dehydration tolerance. Co-silencing of CaFIRF1 and CaSAP14 in pepper increased sensitivity to dehydration, suggesting that CaFIRF1 acts upstream of CaSAP14. A cell-free degradation analysis demonstrated that silencing of CaFIRF1 led to decreased CaSAP14 protein degradation, implicating CaFIRF1 in the regulation of CaSAP14 protein via the 26S proteasomal degradation pathway. Our findings suggest a mechanism by which CaFIRF1 mediates the ubiquitin-dependent proteasomal degradation of CaSAP14, thereby influencing the response of pepper plants to dehydration stress.

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.

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.

5-Aminolevulinic acid treatment mitigates pesticide stress in bean seedlings by regulating stress-related gene expression and retrotransposon movements

Overdoses of pesticides lead to a decrease in the yield and quality of plants, such as beans. The unconscious use of deltamethrin, one of the synthetic insecticides, increases the amount of reactive oxygen species (ROS) by causing oxidative stress in plants. In this case, plants tolerate stress by activating the antioxidant defense mechanism and many genes. 5-Aminolevulinic acid (ALA) improves tolerance to stress by acting exogenously in low doses. There are many gene families that are effective in the regulation of this mechanism. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. In this study, the expression levels of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and stress-associated protein (SAP) genes were determined by Q-PCR in deltamethrin (0.5 ppm) and various doses (20, 40, and 80 mg/l) of ALA-treated bean seedlings. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. It was determined that deltamethrin increased the expression of SOD (1.8-fold), GPX (1.4-fold), CAT (2.7-fold), and SAP (2.5-fold) genes, while 20 and 40 mg/l ALA gradually increased the expression of these genes at levels close to control, but 80 mg/l ALA increased the expression of these genes almost to the same level as deltamethrin (2.1-fold, 1.4-fold, 2.6-fold, and 2.6-fold in SOD, GPX, CAT, and SAP genes, respectively). In addition, retrotransposon-microsatellite amplified polymorphism (REMAP) was performed to determine the polymorphism caused by retrotransposon movements. While deltamethrin treatment has caused a decrease in genomic template stability (GTS) (27%), ALA treatments have prevented this decline. At doses of 20, 40, and 80 mg/L of ALA treatments, the GTS ratios were determined to be 96.8%, 74.6%, and 58.7%, respectively. Collectively, these findings demonstrated that ALA has the utility of alleviating pesticide stress effects on beans.

Comparative and population genomics of buckwheat species reveal key determinants of flavor and fertility

Common buckwheat (Fagopyrum esculentum) is an ancient crop with a world-wide distribution. Due to its excellent nutritional quality and high economic and ecological value, common buckwheat is becoming increasingly important throughout the world. The availability of a high-quality reference genome sequence and population genomic data will accelerate the breeding of common buckwheat, but the high heterozygosity due to the outcrossing nature has greatly hindered the genome assembly. Here we report the assembly of a chromosome-scale high-quality reference genome of F. esculentum var. homotropicum, a homozygous self-pollinating variant of common buckwheat. Comparative genomics revealed that two cultivated buckwheat species, common buckwheat (F. esculentum) and Tartary buckwheat (F. tataricum), underwent metabolomic divergence and ecotype differentiation. The expansion of several gene families in common buckwheat, including FhFAR genes, is associated with its wider distribution than Tartary buckwheat. Copy number variation of genes involved in the metabolism of flavonoids is associated with the difference of rutin content between common and Tartary buckwheat. Furthermore, we present a comprehensive atlas of genomic variation based on whole-genome resequencing of 572 accessions of common buckwheat. Population and evolutionary genomics reveal genetic variation associated with environmental adaptability and floral development between Chinese and non-Chinese cultivated groups. Genome-wide association analyses of multi-year agronomic traits with the content of flavonoids revealed that Fh05G014970 is a potential major regulator of flowering period, a key agronomic trait controlling the yield of outcrossing crops, and that Fh06G015130 is a crucial gene underlying flavor-associated flavonoids. Intriguingly, we found that the gene translocation and sequence variation of FhS-ELF3 contribute to the homomorphic self-compatibility of common buckwheat. Collectively, our results elucidate the genetic basis of speciation, ecological adaptation, fertility, and unique flavor of common buckwheat, and provide new resources for future genomics-assisted breeding of this economically important crop.

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.

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.

Genome-Wide Identification and Characterisation of Stress-Associated Protein Gene Family to Biotic and Abiotic Stresses of Grapevine

Grapevine is one of the earliest domesticated fruit crops and prized for its table fruits and wine worldwide. However, the concurrence of a number of biotic/abiotic stresses affects their yield. Stress-associated proteins (SAPs) play important roles in response to both biotic and abiotic stresses in plants. Despite the growing number of studies on the genomic organisation of SAP gene family in various species, little is known about this family in grapevines (Vitis vinifera L.). In this study, a total of 15 genes encoding proteins possessing A20/AN1 zinc-finger were identified based on the analysis of several genomic and proteomic grapevine databases. According to their structural and phylogenetics features, the identified SAPs were classified into three main groups. Results from sequence alignments, phylogenetics, genomics structure and conserved domains indicated that grapevine SAPs are highly and structurally conserved. In order to shed light on their regulatory roles in growth and development, as well as the responses to biotic/abiotic stresses in grapevine, the expression profiles of SAPs were examined in publicly available microarray data. Bioinformatics analysis revealed distinct temporal and spatial expression patterns of SAPs in various tissues, organs and developmental stages, as well as in response to biotic/abiotic stresses. This study provides insight into the evolution of SAP genes in grapevine and may aid in efforts for further functional identification of A20/AN1-type proteins in the signalling cross-talking induced by biotic/abiotic stresses.

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.

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.

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.

Knockdown of PagSAP11 Confers Drought Resistance and Promotes Lateral Shoot Growth in Hybrid Poplar (Populus alba × Populus tremula var. glandulosa)

Plants have evolved defense mechanisms to overcome unfavorable climatic conditions. The growth and development of plants are regulated in response to environmental stress. In this study, we investigated the molecular and physiological characteristics of a novel gene PagSAP11 in hybrid poplar (Populus alba × Populus tremula var. glandulosa) under drought stress. PagSAP11, a stress-associated protein (SAP) family gene, encodes a putative protein containing an A20 and AN1 zinc-finger domain at its N- and C-termini, respectively. Knockdown of PagSAP11 transgenic poplars (SAP11-Ri) enhanced their tolerance to drought stress compared with wild type plants. Moreover, the RNAi lines showed increased branching of lateral shoots that led to a gain in fresh weight, even when grown in the living modified organism (LMO) field. In SAP11-Ri transgenic plants, the expression levels of genes involved in axillary bud outgrowth and cell proliferation such as DML10, CYP707A and RAX were increased while the DRM gene which involved in bud dormancy was down-regulated. Taken together, these results indicate that PagSAP11 represents a promising candidate gene for engineering trees with improved stress tolerance and growth during unfavorable conditions.

Genome-Wide Analyses of Tea Plant Stress-Associated Proteins (SAPs) Reveal the Role of CsSAP12 in Increased Drought Tolerance in Transgenic Tomatoes

Plant stress-associated proteins (SAPs) contain A20/AN1 zinc finger domains and are involved in plant response to abiotic stresses. In this study, we aimed to explore the biological function of tea plant CsSAPs. A total of 14 CsSAP genes were identified in the tea plant genome using a reference genome database (Camellia sinensis var. sinensis). The CsSAPs were divided into the following two groups: Group I, containing one AN1 domain and/or one A20 domain; and Group II, containing two AN1 domains and/or two C2H2 domains. The sequence alignments and conserved domains analysis indicated that the CsSAPs were highly structurally conserved in terms of amino acid sequence and protein structure. The CsSAPs showed different transcript levels in spatio-temporal expression and in response to cold and drought stress in tea plants. Furthermore, the expression of CsSAP12 was considerably upregulated under drought stress. The overexpression of CsSAP12 in transgenic tomatoes showed increased tolerance to drought stress compared with the wild type. Altogether, the results showed that CsSAP12 might be involved in drought stress. Thus, CsSAP12 might be a target gene in genetic engineering to improve drought tolerance in tea plants.

A stress-associated protein OsSAP8 modulates gibberellic acid biosynthesis by reducing the promotive effect of transcription factor OsbZIP58 on OsKO2

Gibberellic acid (GA) is a vital phytohormone for plant growth and development. GA biosynthesis is a complex pathway regulated by various transcription factors. Here we report a stress-associated protein 8 (OsSAP8), negatively involved in GA biosynthesis. Overexpression of OsSAP8 in rice resulted in a semi-dwarfism phenotype and reduced endogenous GA3 content. In contrast, an OsSAP8 knockout mutant exhibited higher endogenous GA3 content and slightly increased plant height. Sub-cellular localization analysis of OsSAP8 showed that it could enter the nucleus. Based on electrophoretic mobility shift assay and yeast one hybrid experiments, OsSAP8 was found to bind to the cis-acting regulatory element GADOWNAT of ent-kaurene oxidases (KO2, KO3, KO5). The results from dual-luciferase reporter assays showed that OsSAP8 does not activate LUC reporter gene expression. However, it could interact with basic leucine zipper 58 (OsbZIP58), which has strong transcriptional activation potential on OsKO2. Moreover, the interaction between OsSAP8, rice lesion simulating disease 1-like 1 (OsLOL1), and OsbZIP58 could reduce the promotive effect of transcription factor OsbZIP58 on OsKO2. These results provide some new insights on the regulation of GA biosynthesis in rice.

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.

Stress associated proteins coordinate the activation of comprehensive antiviral immunity in Phalaenopsis orchids

Viruses cause severe damage on crops, and identification of key gene(s) that can comprehensively activate antiviral immunity will provide insights for designing effective antiviral strategies. Salicylic acid (SA)-mediated antiviral immunity and RNA interference (RNAi) are two independently discovered antiviral pathways. Previously, we identified the orchid stress-associated protein (SAP), Pha13, which serves as a hub in SA-mediated antiviral immunity. As SAPs exist as a protein family, whether duplicated SAPs have redundant or distinctive functions in antiviral immunity remains elusive. We performed functional assays on orchid Pha21, a homolog of Pha13, using transient and transgenic approaches on orchid, Arabidopsis and Nicotiana benthamiana to overexpress and/or silence Pha21. The SA treatment induced the expression of both Pha13 and Pha21, whereas Pha21 was found to play a key role in the initiation of the RNAi pathway in Phalaenopsis orchids. We demonstrated that Pha21-mediated antiviral immunity and enhancement of the RNAi pathway is conserved between dicotyledons and monocotyledons. We provide new insight that orchid SAPs confer distinctive functions to coordinate both SA-signaling and RNAi for comprehensive activation of antiviral immunity, and this information will help us develop antiviral strategies on crops.

Genome-Wide Identification of Stress-Associated Proteins (SAPs) Encoding A20/AN1 Zinc Finger in Almond (Prunus dulcis) and Their Differential Expression during Fruit Development

Stress-associated proteins (SAPs) are zinc finger proteins involved in the regulation of various stresses in a variety of plant species. A total of nine PdSAP genes were identified in Prunus dulcis. Phylogenetic and synteny analyses were performed to analyze the homology and evolutionary relationship of PdSAP genes. The functions of PdSAP genes were assessed by further analyses, including cis-regulatory elements, gene duplication, gene ontology, gene structure, subcellular localization, and motif pattern. This study found that PdSAP genes were unevenly distributed on chromosomes 2, 3, 6, and 7. Phylogenetic analysis of PdSAP genes with Arabidopsis thaliana and Oryza sativa suggested that six subgroups have a similar pattern of AN1 and A20 domains in each subgroup. PdSAP genes lacked duplicated blocks. The majority of PdSAP genes were localized in the nucleus region. Three hormonal and five stress cis-regulatory elements were found in the upstream promoter region of the PdSAP gene family. RNA-seq analysis revealed differential gene expression of PdSAP genes at days 12, 17, 22, 27, 32, and 37 of fruitlet development after flowering. This study identifies the SAP genes in P. dulcis and also provides insights into the expression of PdSAP genes in abnormal fruitlets with diapause atrophic growth at various developmental stages.

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.

Expression of Specific Alleles of Zinc-Finger Transcription Factors, HvSAP8 and HvSAP16, and Corresponding SNP Markers, Are Associated with Drought Tolerance in Barley Populations

Two genes, HvSAP8 and HvSAP16, encoding Zinc-finger proteins, were identified earlier as active in barley plants. Based on bioinformatics and sequencing analysis, six SNPs were found in the promoter regions of HvSAP8 and one in HvSAP16, among parents of two barley segregating populations, Granal × Baisheshek and Natali × Auksiniai-2. ASQ and Amplifluor markers were developed for HvSAP8 and HvSAP16, one SNP in each gene, and in each of two populations, showing simple Mendelian segregation. Plants of F6 selected breeding lines and parents were evaluated in a soil-based drought screen, revealing differential expression of HvSAP8 and HvSAP16 corresponding with the stress. After almost doubling expression during the early stages of stress, HvSAP8 returned to pre-stress level or was strongly down-regulated in plants with Granal or Baisheshek genotypes, respectively. For HvSAP16 under drought conditions, a high expression level was followed by either a return to original levels or strong down-regulation in plants with Natali or Auksiniai-2 genotypes, respectively. Grain yield in the same breeding lines and parents grown under moderate drought was strongly associated with their HvSAP8 and HvSAP16 genotypes. Additionally, Granal and Natali genotypes with specific alleles at HvSAP8 and HvSAP16 were associated with improved performance under drought via higher 1000 grain weight and more shoots per plant, respectively.

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.

Spermidine Induces Expression of Stress Associated Proteins (SAPs) Genes and Protects Rice Seed from Heat Stress-Induced Damage during Grain-Filling

Heat stress during seed maturation significantly reduced seed size and quality. Polyamines, especially spermidine (Spd), were reported to be closely related to seed development and plant heat tolerance. Stress-associated proteins (SAPs) also played a critical role in plant heat resistance, but the relationship between Spd and SAPs in improving rice tolerance to heat stress during grain filling has not been reported. Our results showed that the external spraying Spd (1.5 mM) significantly increased seed germination rate, germination index, vigor index and 1000-grain weight, significantly increased endogenous Spd, spermine (Spm) content and peroxidase activity; significantly reduced MDA content; and greatly alleviated the impact of heat stress on rice seed quality during grain filling stage as compared with high temperature control. OsSAP5 was the most upregulated expression induced by Spd, and may be mainly involved in the Spd-mediated enhancement of high-temperature resistance during rice seed development. Overexpression of OsSAP5 in Arabidopsis enhanced 1000-grain weight and seed heat resistance. Exogenous Spd alleviated the survival rate and seedling length, reduced MDA content, and upregulated the expression levels of SPDS and SPMS in Atsap4 mutant under high temperature during seed germination. In all, exogenous Spd alleviated the heat damage on seed quality during the grain filling stage and seed germination stage by improving endogenous Spd and Spm. OsSAP5, a key gene induced by Spd, might be involved in the rice heat resistance and seed quality in coordination with Spd and Spm.

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.

Genome-Wide Association Mapping of Salinity Tolerance at the Seedling Stage in a Panel of Vietnamese Landraces Reveals New Valuable QTLs for Salinity Stress Tolerance Breeding in Rice

Rice tolerance to salinity stress involves diverse and complementary mechanisms, such as the regulation of genome expression, activation of specific ion-transport systems to manage excess sodium at the cell or plant level, and anatomical changes that avoid sodium penetration into the inner tissues of the plant. These complementary mechanisms can act synergistically to improve salinity tolerance in the plant, which is then interesting in breeding programs to pyramidize complementary QTLs (quantitative trait loci), to improve salinity stress tolerance of the plant at different developmental stages and in different environments. This approach presupposes the identification of salinity tolerance QTLs associated with different mechanisms involved in salinity tolerance, which requires the greatest possible genetic diversity to be explored. To contribute to this goal, we screened an original panel of 179 Vietnamese rice landraces genotyped with 21,623 SNP markers for salinity stress tolerance under 100 mM NaCl treatment, at the seedling stage, with the aim of identifying new QTLs involved in the salinity stress tolerance via a genome-wide association study (GWAS). Nine salinity tolerance-related traits, including the salt injury score, chlorophyll and water content, and K⁺ and Na⁺ contents were measured in leaves. GWAS analysis allowed the identification of 26 QTLs. Interestingly, ten of them were associated with several different traits, which indicates that these QTLs act pleiotropically to control the different levels of plant responses to salinity stress. Twenty-one identified QTLs colocalized with known QTLs. Several genes within these QTLs have functions related to salinity stress tolerance and are mainly involved in gene regulation, signal transduction or hormone signaling. Our study provides promising QTLs for breeding programs to enhance salinity tolerance and identifies candidate genes that should be further functionally studied to better understand salinity tolerance mechanisms in rice.

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.

Identification and characterization of genes related to salt stress tolerance within segregation distortion regions of genetic map in F2 population of upland cotton

Segregation distortion (SD) is a genetic mechanism commonly found in segregating or stable populations. The principle behind this puzzles many researchers. The F₂ generation developed from wild Gossypium darwinii and G. hirsutum CCRI12 species was used to investigate the possible transcription factors within the segregation distortion regions (SDRs). The 384 out of 2763 markers were distorted in 29 SDRs on 18 chromosomes. Good collinearity was observed among genetic and physical maps of G. hirsutum and G. barbadense syntenic blocks. Total 568 genes were identified from SDRs of 18 chromosomes. Out of these genes, 128 belonged to three top-ranked salt-tolerant gene families. The DUF597 contained 8 uncharacterized genes linked to Pkinase (PF00069) gene family in the phylogenetic tree, while 15 uncharacterized genes clustered with the zinc finger gene family. Two hundred thirty four miRNAs targeted numerous genes, including ghr-miR156, ghr-miR399 and ghr-miR482, while others targeted top-ranked stress-responsive transcription factors. Moreover, these genes were involved in the regulation of numerous stress-responsive cis-regulatory elements. The RNA sequence data of fifteen upregulated genes were verified through the RT-qPCR. The expression profiles of two highly upregulated genes (Gh_D01G2015 and Gh_A01G1773) in salt-tolerant G. darwinii showed antagonistic expression in G. hirsutum. The results indicated that salt-tolerant genes have been possibly transferred from the wild G. darwinii species. A detailed functional analysis of these genes can be carried out which might be helpful in the future for gene cloning, transformation, gene editing and the development of salt-resistant cotton varieties.

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.

Chromosomal introgressions from Oryza meridionalis into domesticated rice Oryza sativa result in iron tolerance

Iron (Fe) toxicity is one of the most common mineral disorders affecting rice (Oryza sativa) production in flooded lowland fields. Oryza meridionalis is indigenous to northern Australia and grows in regions with Fe-rich soils, making it a candidate for use in adaptive breeding. With the aim of understanding tolerance mechanisms in rice, we screened a population of interspecific introgression lines from a cross between O. sativa and O. meridionalis for the identification of quantitative trait loci (QTLs) contributing to Fe-toxicity tolerance. Six putative QTLs were identified. A line carrying one introgression from O. meridionalis on chromosome 9 associated with one QTL was highly tolerant despite very high shoot Fe concentrations. Physiological, biochemical, ionomic, and transcriptomic analyses showed that the tolerance of the introgression lines could partly be explained by higher relative Fe retention in the leaf sheath and culm. We constructed the interspecific hybrid genome in silico for transcriptomic analysis and identified differentially regulated introgressed genes from O. meridionalis that could be involved in shoot-based Fe tolerance, such as metallothioneins, glutathione S-transferases, and transporters from the ABC and MFS families. This work demonstrates that introgressions of O. meridionalis into the O. sativa genome can confer increased tolerance to excess Fe.

Phytohormone-Mediated Molecular Mechanisms Involving Multiple Genes and QTL Govern Grain Number in Rice

Increasing the grain number is the most direct route toward enhancing the grain yield in cereals. In rice, grain number can be amplified through increasing the shoot branching (tillering), panicle branching, panicle length, and seed set percentage. Phytohormones have been conclusively shown to control the above characteristics by regulating molecular factors and their cross-interactions. The dynamic equilibrium of cytokinin levels in both shoot and inflorescence meristems, maintained by the regulation of its biosynthesis, activation, and degradation, determines the tillering and panicle branching, respectively. Auxins and gibberellins are known broadly to repress the axillary meristems, while jasmonic acid is implicated in the determination of reproductive meristem formation. The balance of auxin, gibberellin, and cytokinin determines meristematic activities in the inflorescence. Strigolactones have been shown to repress the shoot branching but seem to regulate panicle branching positively. Ethylene, brassinosteroids, and gibberellins regulate spikelet abortion and grain filling. Further studies on the optimization of endogenous hormonal levels can help in the expansion of the grain yield potential of rice. This review focuses on the molecular machinery, involving several genes and quantitative trait loci (QTL), operational in the plant that governs hormonal control and, in turn, gets governed by the hormones to regulate grain number and yield in rice.

The root-knot nematode effector MiPDI1 targets a stress-associated protein (SAP) to establish disease in Solanaceae and Arabidopsis

Large amounts of effectors are secreted by the oesophageal glands of plant-parasitic nematodes, but their molecular mode of action remains largely unknown. We characterized a Meloidogyne incognita protein disulphide isomerase (PDI)-like effector protein (MiPDI1) that facilitates nematode parasitism. In situ hybridization showed that MiPDI1 was expressed specifically in the subventral glands of M. incognita. It was significantly upregulated during parasitic stages. Immunolocalization demonstrated MiPDI1 secretion in planta during nematode migration and within the feeding cells. Host-induced silencing of the MiPDI1 gene affected the ability of the nematode to infect the host, whereas MiPDI1 expression in Arabidopsis increased susceptibility to M. incognita, providing evidence for a key role of MiPDI1 in M. incognita parasitism. Yeast two-hybrid, bimolecular fluorescence complementation and coimmunoprecipitation assays showed that MiPDI1 interacted with a tomato stress-associated protein (SlSAP12) orthologous to the redox-regulated AtSAP12, which plays an important role in plant responses to abiotic and biotic stresses. SAP12 silencing or knocking out in Nicotiana benthamiana and Arabidopsis increased susceptibility to M. incognita. Our results suggest that MiPDI1 acts as a pathogenicity factor promoting disease by fine-tuning SAP-mediated responses at the interface of redox signalling, defence and stress acclimation in Solanaceae and Arabidopsis.

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.

Molecular study of drought response in the Mediterranean conifer Pinus pinaster Ait.: Differential transcriptomic profiling reveals constitutive water deficit-independent drought tolerance mechanisms

Adaptation of long-living forest trees to respond to environmental changes is essential to secure their performance under adverse conditions. Water deficit is one of the most significant stress factors determining tree growth and survival. Maritime pine (Pinus pinaster Ait.), the main source of softwood in southwestern Europe, is subjected to recurrent drought periods which, according to climate change predictions for the years to come, will progressively increase in the Mediterranean region. The mechanisms regulating pine adaptive responses to environment are still largely unknown. The aim of this work was to go a step further in understanding the molecular mechanisms underlying maritime pine response to water stress and drought tolerance at the whole plant level. A global transcriptomic profiling of roots, stems, and needles was conducted to analyze the performance of siblings showing contrasted responses to water deficit from an ad hoc designed full-sib family. Although P. pinaster is considered a recalcitrant species for vegetative propagation in adult phase, the analysis was conducted using vegetatively propagated trees exposed to two treatments: well-watered and moderate water stress. The comparative analyses led us to identify organ-specific genes, constitutively expressed as well as differentially expressed when comparing control versus water stress conditions, in drought-sensitive and drought-tolerant genotypes. Different response strategies can point out, with tolerant individuals being pre-adapted for coping with drought by constitutively expressing stress-related genes that are detected only in latter stages on sensitive individuals subjected to drought.

Characterization of a novel LmSAP gene promoter from Lobularia maritima: Tissue specificity and environmental stress responsiveness

Halophyte Lobularia maritima LmSAP encodes an A20AN1 zinc-finger stress-associated protein which expression is up-regulated by abiotic stresses and heavy metals in transgenic tobacco. To deepen our understanding of LmSAP function, we isolated a 1,147 bp genomic fragment upstream of LmSAP coding sequence designated as PrLmSAP. In silico analyses of PrLmSAP revealed the presence of consensus CAAT and TATA boxes and cis-regulatory elements required for abiotic stress, phytohormones, pathogen, and wound responses, and also for tissue-specific expression. The PrLmSAP sequence was fused to the β-glucuronidase (gusA) reporter gene and transferred to rice. Histochemical GUS staining showed a pattern of tissue-specific expression in transgenic rice, with staining observed in roots, coleoptiles, leaves, stems and floral organs but not in seeds or in the root elongation zone. Wounding strongly stimulated GUS accumulation in leaves and stems. Interestingly, we observed a high stimulation of the promoter activity when rice seedlings were exposed to NaCl, PEG, ABA, MeJA, GA, cold, and heavy metals (Al3+, Cd2+, Cu2+ and Zn2+). These results suggest that the LmSAP promoter can be a convenient tool for stress-inducible gene expression and is a potential candidate for crop genetic engineering.

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.

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.

A Stress-Associated Protein, PtSAP13, From Populus trichocarpa Provides Tolerance to Salt Stress

The growth and production of poplars are usually affected by unfavorable environmental conditions such as soil salinization. Thus, enhancing salt tolerance of poplars will promote their better adaptation to environmental stresses and improve their biomass production. Stress-associated proteins (SAPs) are a novel class of A20/AN1 zinc finger proteins that have been shown to confer plants' tolerance to multiple abiotic stresses. However, the precise functions of SAP genes in poplars are still largely unknown. Here, the expression profiles of Populus trichocarpa SAPs in response to salt stress revealed that PtSAP13 with two AN1 domains was up-regulated dramatically during salt treatment. The β-glucuronidase (GUS) staining showed that PtSAP13 was accumulated dominantly in leaf and root, and the GUS signal was increased under salt condition. The Arabidopsis transgenic plants overexpressing PtSAP13 exhibited higher seed germination and better growth than wild-type (WT) plants under salt stress, demonstrating that overexpression of PtSAP13 increased salt tolerance. Higher activities of antioxidant enzymes were found in PtSAP13-overexpressing plants than in WT plants under salt stress. Transcriptome analysis revealed that some stress-related genes, including Glutathione peroxidase 8, NADP-malic enzyme 2, Response to ABA and Salt 1, WRKYs, Glutathione S-Transferase, and MYBs, were induced by salt in transgenic plants. Moreover, the pathways of flavonoid biosynthesis and metabolic processes, regulation of response to stress, response to ethylene, dioxygenase activity, glucosyltransferase activity, monooxygenase activity, and oxidoreductase activity were specially enriched in transgenic plants under salt condition. Taken together, our results demonstrate that PtSAP13 enhances salt tolerance through up-regulating the expression of stress-related genes and mediating multiple biological pathways.

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.

Transcriptome analysis and codominant markers development in caper, a drought tolerant orphan crop with medicinal value

Caper (Capparis spinosa L.) is a xerophytic shrub cultivated for its flower buds and fruits, used as food and for their medicinal properties. Breeding programs and even proper taxonomic classification of the genus Capparis has been hampered so far by the lack of reliable genetic information and molecular markers. Here, we present the first genomic resource for C. spinosa, generated by transcriptomic approach and de novo assembly. The sequencing effort produced nearly 80 million clean reads assembled into 124,723 unitranscripts. Careful annotation and comparison with public databases revealed homologs to genes with a key role in important metabolic pathways linked to abiotic stress tolerance and bio-compounds production, such purine, thiamine and phenylpropanoid biosynthesis, α-linolenic acid and lipid metabolism. Additionally, a panel of genes involved in stomatal development/distribution and encoding for Stress Associated Proteins (SAPs) was also identified. We also used the transcriptomic data to uncover novel molecular markers for caper. Out of 50 SSRs tested, 14 proved polymorphic and represent the first set of SSR markers for the genus Capparis. This transcriptome will be an important contribution to future studies and breeding programs for this orphan crop, aiding to the development of improved varieties to sustain agriculture in arid conditions.

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.