Differential expression of salt-responsive genes to salinity stress in salt-tolerant and salt-sensitive rice (Oryza sativa L.) at seedling stage

Overexpression of OsDUF6 increases salt stress tolerance in rice

BACKGROUND

Soil salinity is one of the primary environmental stresses faced in rice production. When plants are exposed to salt stress, a series of cellular balances will be disrupted. Dufulin is an immune-induced antiviral agent used in plants. The DUF gene family influences plant response to abiotic stress, and the functional role of OsDUF6(ABA98726.1) in rice response to salt stress is being investigated here.

RESULTS

Based on the transcriptome analysis of Dufulin treatment in inducing salt tolerance in rice, we selected the OsDUF6 protein located on the cell membrane and studied its molecular function by overexpressing OsDUF6. Salt-induced decreases in root, stem, and leaf length and increased leaf yellowing rate and Na+ concentration in the wild-type plant were mitigated in the overexpressed lines. OsDUF6 overexpression increased the enzymatic antioxidant activities of superoxide dismutase, peroxidase, catalase, and phenylalanine ammonia-lyase. OsDUF6 also played a positive role in Na+ transport as reflected by the increased growth of a salt-sensitive yeast mutant complemented with OsDUF6 in the presence of salt stress. In addition, Reverse transcription quantitative PCR analysis confirmed that the overexpression of OsDUF6 significantly changed the expression level of other genes related to growth and stress tolerance.

CONCLUSIONS

Combined with previously published data, our results supported the observation that OsDUF6 is an important functional factor in Dufulin-induced promotion of salt stress tolerance in rice.

High throughput phenotyping of functional traits and key indices for selection of salt tolerant Mustard [Brassica juncea (L.) Czern & Coss] genotypes

The current scanty knowledge about the salt tolerance mechanism underlying the ability of plants to tolerate salt stress hinders the potential production of numerous crops, including Indian mustard. To explore the traits and mechanism for salt tolerance, high throughput phenotyping of 250 stabilized F7:8 recombinant inbred lines (RILs) mapping population of Indian mustard were conducted under control and salinity (ECiw 12 dS m-1 ) for 54 morpho-physio-seed-quality traits. Most of the traits were reduced with variable percentages under salt stress. The stress tolerance index (STI) of YPP showed a significant negative association with Na+ concentration of root (RNa), indicating that RILs with low Na+ concentration have high seed yield and a positive significant association with STI of yield-related traits, photosynthesis rate (Pn), intrinsic water use efficiency (inWUE), fresh weight of upper leaf (USFW), fresh weight of branches (BrFW), fresh weight of basal leaf (BLFW), and fresh weight of middle leaf (MLFW) revealed that by improving these traits seed yield per plant (YPP) was improved. Based on principal component analysis (PCA) of 54 STI and new index composite selection index (CSI), RILs viz., R114, R150, R164, R170, and R206 were identified as stable performers which can be exploited for quantitative trait loci (QTLs)/gene discovery and serve as potential donors to combat salt stress. Our research will serve to determine the relative importance of different functional traits of salt tolerance mechanisms that can be used to screen colossal germplasm.

Multi-index fuzzy comprehensive evaluation model with information entropy of alfalfa salt tolerance based on LiDAR data and hyperspectral image data

Rapid, non-destructive and automated salt tolerance evaluation is particularly important for screening salt-tolerant germplasm of alfalfa. Traditional evaluation of salt tolerance is mostly based on phenotypic traits obtained by some broken ways, which is time-consuming and difficult to meet the needs of large-scale breeding screening. Therefore, this paper proposed a non-contact and non-destructive multi-index fuzzy comprehensive evaluation model for evaluating the salt tolerance of alfalfa from Light Detection and Ranging data (LiDAR) and HyperSpectral Image data (HSI). Firstly, the structural traits related to growth status were extracted from the LiDAR data of alfalfa, and the spectral traits representing the physical and chemical characteristics were extracted from HSI data. In this paper, these phenotypic traits obtained automatically by computation were called Computing Phenotypic Traits (CPT). Subsequently, the multi-index fuzzy evaluation system of alfalfa salt tolerance was constructed by CPT, and according to the fuzzy mathematics theory, a multi-index Fuzzy Comprehensive Evaluation model with information Entropy of alfalfa salt tolerance (FCE-E) was proposed, which comprehensively evaluated the salt tolerance of alfalfa from the aspects of growth structure, physiology and biochemistry. Finally, comparative experiments showed that: (1) The multi-index FCE-E model based on the CPT was proposed in this paper, which could find more salt-sensitive information than the evaluation method based on the measured Typical Phenotypic Traits (TPT) such as fresh weight, dry weight, water content and chlorophyll. The two evaluation results had 66.67% consistent results, indicating that the multi-index FCE-E model integrates more information about alfalfa and more comprehensive evaluation. (2) On the basis of the CPT, the results of the multi-index FCE-E method were basically consistent with those of Principal Component Analysis (PCA), indicating that the multi-index FCE-E model could accurately evaluate the salt tolerance of alfalfa. Three highly salt-tolerant alfalfa varieties and two highly salt-susceptible alfalfa varieties were screened by the multi-index FCE-E method. The multi-index FCE-E method provides a new method for non-contact non-destructive evaluation of salt tolerance of alfalfa.

Rice straw based silicon nanoparticles improve morphological and nutrient profile of rice plants under salinity stress by triggering physiological and genetic repair mechanisms

The agricultural sector is facing numerous challenges worldwide, owing to global climate change and limited resources. Crop production is limited by numerous abiotic constraints. Among them, salinity stress as a combination of osmotic and ionic stress adversely influences the physiological and biochemical processes of the plant. Nanotechnology facilitates the production of crops either directly by eradicating the losses due to challenging environmental conditions or indirectly by improving tolerance against salinity stress. In this study, the protective role of silicon nanoparticles (SiNPs) was determined in two rice genotypes, N-22 and Super-Bas, differing in salinity tolerance. The SiNPs were confirmed through standard material characterization techniques, which showed the production of spherical-shaped crystalline SiNPs with a size in the range of 14.98-23.74 nm, respectively. Salinity stress adversely affected the morphological and physiological parameters of both varieties, with Super-Bas being more affected. Salt stress disturbed the ionic balance by minimizing the uptake of K+ and Ca2+ contents and increased the uptake of Na+ in plants. Exogenous SiNPs alleviated the toxic effects of salt stress and promoted the growth of both N-22 and Super-Bas, chlorophyll contents (16% and 13%), carotenoids (15% and 11%), total soluble protein contents (21% and 18%), and the activities of antioxidant enzymes. Expression analysis from quantitative real-time PCR showed that SiNPs relieved plants from oxidative bursts by triggering the expression of HKT genes. Overall, these findings demonstrate that SiNPs significantly alleviated salinity stress by triggering physiological and genetic repair mechanisms, offering a potential solution for food security.

Comparative transcriptomic profiling reveals differentially expressed genes and important related metabolic pathways in shoots and roots of a Saudi wheat cultivar (Najran) under salinity stress

High salinity of soil is a threatening constraint for agricultural output worldwide. The adverse effects of salt stress on plants can be revealed in different manners, from phenotypic to genetic changes. A comparative RNA-Sequencing analysis was done in roots and shoots of bread wheat, Najran cultivar between plants grown under unstressed control condition (0 mM NaCl) and salt treatment (200 mM NaCl). More than 135 million and 137 million pair-end reads were obtained from root and shoot samples, respectively. Of which, the mapped reads to Triticum aestivum genome IWGSC_V51 ranged from 83.9% to 85% in the root and 71.6% to 79% in the shoot. Interestingly, a comparison of transcriptomic profiling identified that total number of significantly differentially expressed genes (DEGs) examined in the roots was much higher than that found in the shoots under NaCl treatment, 5829 genes were differentially expressed in the roots whereas 3495 genes in the shoots. The salt-induced change in the transcriptome was confirmed by RT-qPCR using a set of randomly selected genes. KEGG enrichment analysis classified all DEGs in both roots and shoots into 25 enriched KEGG pathways from three main KEGG classes: Metabolism, organismal systems and genetic information processing. According to that, the most significantly regulated pathways in the root and shoot tissues were glutathione metabolism and biosynthesis of secondary metabolites such as phenylpropanoids and galactose metabolism suggesting that these pathways might participate in wheat salt tolerance. The findings highlight the importance of the control of oxidative stress via Glutathione and phenylpropanoids and the regulation of galactose metabolism in the roots and shoots for salt-tolerance in wheat. They open promising prospects for engineering salt-tolerance in this important crop via targeted improvement of the regulation of key genes in the production of these compounds.

Humic Acid Modulates Ionic Homeostasis, Osmolytes Content, and Antioxidant Defense to Improve Salt Tolerance in Rice

The sensitivity of rice plants to salinity is a major challenge for rice growth and productivity in the salt-affected lands. Priming rice seeds in biostimulants with stress-alleviating potential is an effective strategy to improve salinity tolerance in rice. However, the mechanisms of action of these compounds are not fully understood. Herein, the impact of priming rice seeds (cv. Giza 179) with 100 mg/L of humic acid on growth and its underlaying physiological processes under increased magnitudes of salinity (EC = 0.55, 3.40, 6.77, 8.00 mS/cm) during the critical reproductive stage was investigated. Our results indicated that salinity significantly reduced Giza 179 growth indices, which were associated with the accumulation of toxic levels of Na⁺ in shoots and roots, a reduction in the K⁺ and K⁺/Na⁺ ratio in shoots and roots, induced buildup of malondialdehyde, electrolyte leakage, and an accumulation of total soluble sugars, sucrose, proline, and enzymic and non-enzymic antioxidants. Humic acid application significantly increased growth of the Giza 179 plants under non-saline conditions. It also substantially enhanced growth of the salinity-stressed Giza 179 plants even at 8.00 mS/cm. Such humic acid ameliorating effects were associated with maintaining ionic homeostasis, appropriate osmolytes content, and an efficient antioxidant defense system. Our results highlight the potential role of humic acid in enhancing salt tolerance in Giza 179.

OsMBTB32, a MATH-BTB domain-containing protein that interacts with OsCUL1s to regulate salt tolerance in rice

MATH-BTB proteins are involved in a variety of cellular processes that regulate cell homeostasis and developmental processes. Previous studies reported the involvement of BTB proteins in the development of various organs in plants; however, the function of BTB proteins in salt stress is less studied. Here, we found a novel MATH-BTB domain-containing OsMBTB32 protein that was highly expressed in leaf, root, and shoot. The up-regulation of the OsMBTB32 transcript in 2-week-old seedlings under salt stress suggests the significant role of the OsMBTB32 gene in salinity. The OsMBTB32 transgenic seedlings (OE and RNAi) exhibited significant differences in various phenotypes, including plumule, radical, primary root, and shoot length, compared to WT seedlings. We further found that OsCUL1 proteins, particularly OsCUL1-1 and OsCUL1-3, interact with OsMBTB32 and may suppress the function of OsMBTB32 during salt stress. Moreover, OsWRKY42, a homolog of ZmWRKY114 which negatively regulates salt stress in rice, directly binds to the W-box of OsCUL1-1 and OsCUL1-3 promoters to promote the interaction of OsCUL1-1 and OsCUL1-3 with OsMBTB32 protein in rice. The overexpression of OsMBTB32 and OsCUL1-3 further confirmed the function of OsMBTB32 and OsCUL1s in salt tolerance in Arabidopsis. Overall, the findings of the present study provide promising knowledge regarding the MATH-BTB domain-containing proteins and their role in enhancing the growth and development of rice under salt stress.MATH-BTB proteins are involved in a variety of cellular processes that regulate cell homeostasis and developmental processes. Previous studies reported the involvement of BTB proteins in the development of various organs in plants; however, the function of BTB proteins in salt stress is less studied. Here, we found a novel MATH-BTB domain-containing OsMBTB32 protein that was highly expressed in leaf, root, and shoot. The up-regulation of the OsMBTB32 transcript in 2-week-old seedlings under salt stress suggests the significant role of the OsMBTB32 gene in salinity. The OsMBTB32 transgenic seedlings (OE and RNAi) exhibited significant differences in various phenotypes, including plumule, radical, primary root, and shoot length, compared to WT seedlings. We further found that OsCUL1 proteins, particularly OsCUL1-1 and OsCUL1-3, interact with OsMBTB32 and may suppress the function of OsMBTB32 during salt stress. Moreover, OsWRKY42, a homolog of ZmWRKY114 which negatively regulates salt stress in rice, directly binds to the W-box of OsCUL1-1 and OsCUL1-3 promoters to promote the interaction of OsCUL1-1 and OsCUL1-3 with OsMBTB32 protein in rice. The overexpression of OsMBTB32 and OsCUL1-3 further confirmed the function of OsMBTB32 and OsCUL1s in salt tolerance in Arabidopsis. Overall, the findings of the present study provide promising knowledge regarding the MATH-BTB domain-containing proteins and their role in enhancing the growth and development of rice under salt stress.

Validation of a QTL on Chromosome 1DS Showing a Major Effect on Salt Tolerance in Winter Wheat

Salt stress is one the most destructive abiotic stressors, causing yield losses in wheat worldwide. A prerequisite for improving salt tolerance is the identification of traits for screening genotypes and uncovering causative genes. Two populations of F₃ lines developed from crosses between sensitive and tolerant parents were tested for salt tolerance at the seedling stage. Based on their response, the offspring were classified as salt sensitive and tolerant. Under saline conditions, tolerant genotypes showed lower Na⁺ and proline content but higher K⁺, higher chlorophyll content, higher K⁺/Na⁺ ratio, higher PSII activity levels, and higher photochemical efficiency, and were selected for further molecular analysis. Five stress responsive QTL identified in a previous study were validated in the populations. A QTL on the short arm of chromosome 1D showed large allelic effects in several salt tolerant related traits. An expression analysis of associated candidate genes showed that TraesCS1D02G052200 and TraesCS5B02G368800 had the highest expression in most tissues. Furthermore, qRT-PCR expression analysis revealed that ZIP-7 had higher differential expressions under saline conditions compared to KefC, AtABC8 and 6-SFT. This study provides information on the genetic and molecular basis of salt tolerance that could be useful in development of salt-tolerant wheat varieties.

Full-Length Transcriptomics Reveals Complex Molecular Mechanism of Salt Tolerance in Bromus inermis L

Bromus inermis L. (commonly known as smooth bromegrass) is a grass species with high nutritional value, great palatability, cold tolerance, and grazing resistance, which has been widely cultivated for pasture and sand fixation in northern and northwestern China. Salt stress is a main environmental factor limiting growth and production of smooth bromegrass. In this study, we performed PacBio Iso-Seq to construct the first full-length transcriptome database for smooth bromegrass under 300 mM NaCl treatment at different time points. Third-generation full-length transcriptome sequencing yielded 19.67 G polymerase read bases, which were assembled into 355,836 full-length transcripts with an average length of 2,542 bp. A total of 116,578 differentially expressed genes were obtained by comparing the results of third-generation sequencing and second-generation sequencing. GO and KEGG enrichment analyses revealed that multiple pathways were differently activated in leaves and roots. In particular, a number of genes participating in the molecular network of plant signal perception, signal transduction, transcription regulation, antioxidant defense, and ion regulation were affected by NaCl treatment. In particular, the CBL-CIPK, MAPK, ABA signaling network, and SOS core regulatory pathways of Ca²⁺ signal transduction were activated to regulate salt stress response. In addition, the expression patterns of 10 salt-responsive genes were validated by quantitative real-time PCR, which were consistent with those detected by RNA-Seq. Our results reveal the molecular regulation of smooth bromegrass in response to salt stress, which are important for further investigation of critical salt responsive genes and molecular breeding of salt-tolerant smooth bromegrass.

Salt stress responses and SNP-based phylogenetic analysis of Thai rice cultivars

Genetic diversity is important for developing salt-tolerant rice (Oryza sativa L.) cultivars. Certain Thai rice accessions display salt tolerance at the adult or reproductive stage, but their response to salinity at the seedling stage is unknown. In this study, a total of 10 rice cultivars/line, including eight Thai cultivars and standard salt-tolerant cultivar and susceptible line, were screened using a hydroponic system to identify salt-tolerant genotypes at the seedling stage. Different morphophysiological indicators were used to classify tolerant and susceptible genotypes. Phylogenetic analyses were performed to determine the evolutionary relationships between the cultivars. Results showed that 'Lai Mahk', 'Jao Khao', 'Luang Pratahn', and 'Ma Gawk' exhibited salt stress tolerance comparable with the standard salt-tolerance check 'Pokkali'. Whole-exome single-nucleotide polymorphism (SNP)-based phylogenetic analysis showed that the Thai rice cultivars were monophyletic and distantly related to Pokkali and IR29. Lai Mahk and Luang Pratahn were found closely related when using the whole-exome SNPs for the analysis. This is also the case for the analysis of SNPs from 164 salt-tolerance genes and transcription regulatory genes. The tolerant cultivars shared the same haplotype for 16 genes. Overall, the findings of this study identified four salt-stress-tolerant Thai rice cultivars, which could be used in rice breeding programs for salinity tolerance.

Discovery of DNA polymorphisms via whole genome resequencing and their functional relevance in salinity stress response in chickpea

Salinity stress is one of the major constraints for plant growth and yield. The salinity stress response of different genotypes of crop plants may largely be governed by DNA polymorphisms. To determine the molecular genetic factors involved in salinity stress tolerance in chickpea, we performed a whole genome resequencing data analysis of three each of salinity-sensitive and salinity-tolerant genotypes. A total of 6173 single nucleotide polymorphisms and 920 insertions and deletions differentiating the chickpea genotypes with contrasting salinity stress responses were identified. Gene ontology analysis revealed the enrichment of functional terms related to stress response and development among the genes harboring DNA polymorphisms in their promoter and/or coding regions. DNA polymorphisms located within the cis-regulatory motifs of the quantitative trait loci (QTL)-associated and abiotic stress related genes were identified, which may influence salinity stress response via modulating binding affinity of the transcription factors. Several genes including QTL-associated and abiotic stress response related genes harboring DNA polymorphisms exhibited differential expression in response to salinity stress especially at the reproductive stage of development in the salinity-tolerant genotype. Furthermore, effects of non-synonymous DNA polymorphisms on mutational sensitivity and structural integrity of the encoded proteins by the candidate QTL-associated and abiotic stress response related genes were revealed. The results suggest that DNA polymorphisms may determine salinity stress response via influencing differential gene expression in genotype and/or stage-dependent manner. Altogether, we provide a high-quality set of DNA polymorphisms and candidate genes that may govern salinity stress tolerance in chickpea.

Effects of salt stress on the photosynthetic physiology and mineral ion absorption and distribution in white willow (Salix alba L.)

Objective

The purpose of this study was to explore the adaptive mechanism underlying the photosynthetic characteristics and the ion absorption and distribution of white willow (Salix alba L.) in a salt stress environment in cutting seedlings. The results lay a foundation for further understanding the distribution of sodium chloride and its effect on the photosynthetic system.

Method

A salt stress environment was simulated in a hydroponics system with different NaCl concentrations in one-year-old Salix alba L.branches as the test materials. Their growth, ion absorption, transport and distribution in the roots and leaves, and the changes in the photosynthetic fluorescence parameters were studied after 20 days under hydroponics.

Results

The results show that The germination and elongation of roots are promoted in the presence of 171mM NaCl, but root growth is comprehensively inhibited under increasing salt stress. Under salt stress, Na⁺ accumulates significantly in the roots and leaves, and the Na⁺ content and the Na⁺/K⁺ and Na⁺/Ca²⁺ root ratios are significantly greater than those in the leaves. When the NaCl concentration is ≤ 342mM, Salix alba can maintain relatively stable K⁺ and Ca²⁺ contents in its leaves by improving the selective absorption and accumulation of K⁺ and Ca²⁺ and adjusting the transport capacity of mineral ions to aboveground parts, while K⁺ and Ca²⁺ levels are clearly decreased under high salt stress. With increasing salt concentrations, the net photosynthetic rate (P_n), transpiration rate (E) and stomatal conductance (g_s) of leaves decrease gradually overall, and the intercellular CO₂ concentration (C_i) first decreases and then increases. When the NaCl concentration is < 342mM, the decrease in leaf P_n is primarily restricted by the stomata. When the NaCl concentration is > 342mM, the decrease in the P_n is largely inhibited by non-stomatal factors. Due to the salt stress environment, the OJIP curve (Rapid chlorophyll fluorescence) of Salix alba turns into an OKJIP curve. When the NaCl concentration is > 171mM, the fluorescence values of points I and P decrease significantly, which is accompanied by a clear inflection point (K). The quantum yield and energy distribution ratio of the PSⅡ reaction center change significantly (φPo, Ψo and φEo show an overall downward trend while φDo is promoted). The performance index and driving force (PI_ABS, PI_CSm and DF_CSm) decrease significantly when the NaCl concentration is > 171mM, indicating that salt stress causes a partial inactivation of the PSII reaction center, and the functions of the donor side and the recipient side are damaged.

Conclusion

The above results indicate that Salix alba can respond to salt stress by intercepting Na⁺ in the roots, improving the selective absorption of K⁺ and Ca²⁺ and the transport capacity to the above ground parts of the plant, and increasing φDo, thus shows an ability to self-regulate and adapt.

GWAS and transcriptomic integrating analysis reveals key salt-responding genes controlling Na+ content in barley roots

Salt stress is one of the major environmental restricts for crop production and food safety. Barley (Hordeum vulgare L.) is the most salt-tolerant cereal crop, which could be the pioneer for shifting agricultural crop production to marginal saline lands. However, probably due to high genetic complexity of salinity tolerance trait, the progress in the identification of salt-tolerant locus or genes of barley roots moves slowly. Here, we determined physiological and ionic changes in mini-core barley accessions under salt conditions. Na⁺ content was lower in whole-plant but higher in roots of the salt tolerant genotypes than sensitive ones under salt stress. Genome-wide association study (GWAS) analysis identified 43 significant SNPs out of 12,564 SNPs and 215 candidate genes (P < 10^-3) in the roots of worldwide barley accessions, highly associated with root relative dry weight (RDW) and Na⁺ content after hydroponic salinity in greenhouse and growth chamber. Meanwhile, transcriptomic analysis (RNA-Seq) identified 3217 differentially expression genes (DEGs) in barley roots induced by salt stress, mainly enriched in metabolism and transport processes. After GWAS and RNA-Seq integrating analysis, 39 DEGs were verified by qRT-PCR as salt-responding genes, including CYPs, LRR-KISS and CML genes, mostly related to the signal regulation. Taken together, current results provide genetic map-based genes or new locus useful for improving salt tolerance in crop and contributing to the utilization of saline soils.

Physiological and Biochemical Traits of Two Major Arabidopsis Accessions, Col-0 and Ws, Under Salinity

Salinity affects plant growth and development as shown with the glycophyte model plant, Arabidopsis thaliana (Arabidopsis). Two Arabidopsis accessions, Wassilewskija (Ws) and Columbia (Col-0), are widely used to generate mutants available from various Arabidopsis seed resources. However, these two ecotypes are known to be salt-sensitive with different degrees of tolerance. In our study, 3-week-old Col-0 and Ws plants were treated with and without 150 mM NaCl for 48, 72, or 96 h, and several physiological and biochemical traits were characterized on shoots to identify any specific traits in their tolerance to salinity. Before salt treatment was carried out, a different phenotype was observed between Col-0 and Ws, whose main inflorescence stem became elongated in contrast to Col-0, which only displayed rosette leaves. Our results showed that Col-0 and Ws were both affected by salt stress with limited growth associated with a reduction in nutrient uptake, a degradation of photosynthetic pigments, an increase in protein degradation, as well as showing changes in carbohydrate metabolism and cell wall composition. These traits were often more pronounced in Col-0 and occurred usually earlier than in Ws. Tandem Mass Tags quantitative proteomics data correlated well with the physiological and biochemical results. The Col-0 response to salt stress was specifically characterized by a greater accumulation of osmoprotectants such as anthocyanin, galactinol, and raffinose; a lower reactive oxygen detoxification capacity; and a transient reduction in galacturonic acid content. Pectin degradation was associated with an overaccumulation of the wall-associated kinase 1, WAK1, which plays a role in cell wall integrity (CWI) upon salt stress exposure. Under control conditions, Ws produced more antioxidant enzymes than Col-0. Fewer specific changes occurred in Ws in response to salt stress apart from a higher number of different fascilin-like arabinogalactan proteins and a greater abundance of expansin-like proteins, which could participate in CWI. Altogether, these data indicate that Col-0 and Ws trigger similar mechanisms to cope with salt stress, and specific changes are more likely related to the developmental stage than to their respective genetic background.

Evolution and identification of DREB transcription factors in the wheat genome: modeling, docking and simulation of DREB proteins associated with salt stress

Soil salinity and the resulting salt stress it imposes on crop plants is a major problem for modern agriculture. Understanding how salt tolerance mechanisms in plants are regulated is therefore important. One regulatory mechanism is the APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription factor family, including dehydration responsive element binding (DREB) transcription factors. By binding to DNA, specifically upstream of genes that play roles in salt tolerance pathways, DREB proteins upregulate expression of these genes. DREB in Triticum aestivum (wheat) cluster in sub-groups and in this study by scanning the recently extended predicted proteome of wheat for DREB, we increased the number of members of this sub-family. Using the wheat genome, we identified 576 genes coding for the AP2 domain of which 508 were identified to have one AP2 domain, a characteristic of the DREB/ERF subfamily. We confirmed the existing four sub-groups by sequence-based phylogenetic analyses but also identified 32 new DREB subfamily members, not belonging to any known sub-group. Transcription factor profile inference analysis identified two genes, TraesCS2B02G002700 and TraesCS2D02G015200, being homologous to DREB1A of Arabidopsis thaliana. Based on molecular simulation (25 ns) analysis, TraesCS2B02G002700 with a CCGAC motif was observed to interact very stably with DNA. In silico mutational analysis at the 19^th position in the DREB domain of TraesCS2B02G002700-DNA complex indicated this as a stable part for recognizing and forming interaction with DNA. Moreover, six target genes were predicted having an upstream CCGAC motif regulated by TraesCS2B02G002700. Our study provides an overall framework for exploring the transcription factors in plants and identifying e.g. potential salt stress target genes.Communicated by Ramaswamy H. Sarma.

Soil salinity under climate change: Challenges for sustainable agriculture and food security

Soil salinity is one of the major and widespread challenges in the recent era that hinders global food security and environmental sustainability. Worsening the situation, the harmful impacts of climate change accelerate the development of soil salinity, potentially spreading the problem in the near future to currently unaffected regions. This paper aims to synthesise information from published literature about the extent, development mechanisms, and current mitigation strategies for tackling soil salinity, highlighting the opportunities and challenges under climate change situations. Mitigation approaches such as application of amendments, cultivation of tolerant genotypes, suitable irrigation, drainage and land use strategies, conservation agriculture, phytoremediation, and bioremediation techniques have successfully tackled the soil salinity issue, and offered associated benefits of soil carbon sequestration, and conservation and recycling of natural resources. These management practices further improve the socio-economic conditions of the rural farming community in salt-affected areas. We also discuss emerging reclamation strategies such as saline aquaculture integrated with sub surface drainage, tolerant microorganisms integrated with tolerant plant genotypes, integrated agro-farming systems that warrant future research attention to restore the agricultural sustainability and global food security under climate change scenarios.

Expression level of Na+ homeostasis-related genes and salt-tolerant abilities in backcross introgression lines of rice crop under salt stress at reproductive stage

Salt stress in the rice field is one of the most common abiotic stresses, reducing crop productivity, especially at reproductive stage, which is very sensitive to salt stress. The aim of this investigation was to study mRNA-related Na⁺ uptake/translocation and Na⁺ enrichment in the cellular level, leading to physiological changes, growth characteristics, and yield attributes in FL530 [salt-tolerant genotype; carrying SKC1 (in relation to high-affinity potassium transporters controlling Na⁺ and K⁺ translocation) and qSt1b (linking to salt injury score) QTLs] and KDML105 (salt-sensitive cultivar; lacking both QTLs) parental lines and 221-48 (carrying SKC1 and qSt1b QTLs) derived from BILs (backcross introgression lines) at 50% flowering of rice, under 150-mM NaCl until harvesting process. The upregulation of OsHKT1;5 (mediating Na⁺ exclusion into xylem parenchyma cells) and OsNHX1 (Na⁺/H⁺ exchanger to secrete Na⁺ into vacuole) and downregulation of OsHKT2;1 and OsHKT2;2 (mediating Na⁺ restriction in the roots, leaf sheath and older leaves) in cvs. FL530 and 221-48 (+ SKC1; + qSt1b) under salt stress were observed. It restricted Na⁺ level in flag leaf, thereby preventing salt toxicity, as indicated by maintenance of photon yield of PSII (Φ_PSII), net photosynthetic rate (P_n), transpiration rate (E) and overall growth performances. In contrast, Na⁺ enrichment in flag leaf of cv. KDML105 (-SKC1;-qSt1b) caused the reduction in Φ_PSII by 30.5% over the control, leading to the reduction in P_n by 62.3%, in seed sterility by 88.2%, and yield loss by 85.1%. Moreover, the negative relationships between Na⁺ enrichment in flag leaf, physiological changes, and yield traits in rice crop grown under salt stress were demonstrated. Based on this investigation, rice genotype 221-48 was found to possess salt-tolerant traits at reproductive stage and thus could prove to be a potential candidate for future breeding programs.

Traditional rice landraces in Lei-Qiong area of South China tolerate salt stress with strong antioxidant activity

Salt stress, causing serious loss on crop productions, is one of the most important environmental stresses throughout the world. The aim of this study is to select salt-tolerant traditional rice resources collected from Lei-Qiong area of South China and investigate their physiological performances and biochemical regulations during salt stress response, together with two well-known international varieties, Nona Bokra (salt-tolerant sample) and IR29 (salt-sensitive sample). After comprehensive analyses, we discovered that two Lei-Qiong traditional salt-tolerant rice samples showed less growth inhibition by salt stress during both germination and seedling stage, in comparison with other rice samples. Moreover, there were less chlorosis symptoms in these two kinds of salt tolerant rice under salt stress, corresponding to their better water-holding capacity. We measured malondialdehyde and proline contents, and activities of CAT and POD of seedlings treated with 100 mM NaCl for 5 dand 10 d, respectively. Interestingly, less cellular membrane damage and stronger antioxidant enzyme system were found in the two Lei-Qiong rice samples. Our study suggests that traditional rice landrace growing onshore of Lei-Qiong area in China possesses good salt-tolerant capacity, which could be attributed to their efficient antioxidant enzyme system.

Expression levels of the Na+/K+ transporter OsHKT2;1 and vacuolar Na+/H+ exchanger OsNHX1, Na enrichment, maintaining the photosynthetic abilities and growth performances of indica rice seedlings under salt stress

Salt affected soil inhibits plant growth, development and productivity, especially in case of rice crop. Ion homeostasis is a candidate defense mechanism in the salt tolerant plants or halophyte species, where the salt toxic ions are stored in the vacuoles. The aim of this investigation was to determine the OsNHX1 (a vacuolar Na⁺/H⁺ exchanger) and OsHKT2;1 (Na⁺/K⁺ transporter) regulation by salt stress (200 mM NaCl) in two rice cultivars, i.e. Pokkali (salt tolerant) and IR29 (salt susceptible), the accumulation of Na⁺ in the root and leaf tissues using CoroNa Green^® staining dye and the associated physiological changes in test plants. Na⁺ content was largely increased in the root tissues of rice seedlings cv. Pokkali (15 min after salt stress) due to the higher expression of OsHKT2;1 gene (by 2.5 folds) in the root tissues. The expression of OsNHX1 gene in the leaf tissues was evidently increased in salt stressed seedlings of Pokkali, whereas it was unchanged in salt stressed seedlings of IR29. Na⁺ in the root tissues of both Pokkali and IR29 was enriched, when subjected to 200 mM NaCl for 12 h and easily detected in the leaf tissues of salt stressed plants exposed for 24 h, especially in cv. Pokkali. Moreover, the overexpression of OsNHX1 gene regulated the translocation of Na⁺ from root to leaf tissues, and compartmentation of Na⁺ into vacuoles, thereby maintaining the photosynthetic abilities in cv. Pokkali. Overall growth performance, maximum quantum yield (F_v/F_m), photon yield of PSII (Φ_PSII) and net photosynthetic rate (P_n) was improved in salt stressed leaves of Pokkali than those in salt stressed IR29.

Host Plant Salinity Stress Affects the Development and Population Parameters of Nilaparvata lugens (Hemiptera: Delphacidae)

Salinization is one of the most critical abiotic stress factors for crops and a rising setback in agro-ecosystems. Changes in weather, land usage, and the salinization of irrigation water are increasing soil salinity of many farmlands. Increased soil salinity alters the plant quality, which subsequently may trigger bottom-up effects on herbivorous insect. We examined the bottom-up effect of salinity stress on population parameters of the brown planthopper (BPH), Nilaparvata lugens through rice (Oryza sativa L.) plant. The results revealed that salinity interfered with egg hatching of BPH. The nymphal development period, adult longevity, and oviposition were also influenced by salinity. Notable differences appeared in the intrinsic growth rate (r), the finite increase rate (λ) and the net reproduction rate (R0) of BPH, and a concentration-dependent effect was detected. Although salinity adversely affected BPH development, population projection predicted a successful growth of the BPH population in a relatively short time under the treatment of low and medium levels of salinity (6, 8, and 10 dS/m of NaCl), whereas higher salt concentrations (12 and 14 dS/m) lead to significant fitness costs in BPH populations. Our study predicts that BPH could become a problem in areas with lower and medium salinity and that those planthoppers may exacerbate the negative effects of salinity for rice production. This study will provide valuable information for understanding the field abundance and distribution of BPH on saline rice field, thus contributing to the development of eco-friendly strategies to manage this pest in saline ecosystems.

Effects of cerium oxide on rice seedlings as affected by co-exposure of cadmium and salt

Effects of CeO₂ NPs (200 mg.L^-1) on rice (Oryza sativa L.) alone or co-exposure with cadmium (Cd) and salt (sodium chloride, NaCl) were investigated in hydroponic systems for two weeks. Physiological results show that rice biomass was significantly inhibited when NaCl or CdCl₂ added alone or in co-exposure treatment. CeO₂ NPs significantly relieve the chlorophyll damage under CdCl₂ environmental stress. The presence of CeO₂ NPs alleviated both stressors induced damages to rice as indicated by the reduced proline level. Additionally, CeO₂ NPs triggered the antioxidant defense systems to counteract the oxidative stress caused by NaCl and CdCl₂. The level of 8-OHdG, one of the most important indicators for genotoxicity, in rice suggest that the presence of CeO₂ NPs reduced the DNA damage in NaCl treated rice. Elemental analysis indicated that co-exposure to NaCl and CdCl₂ slightly decreased the Cd content as compared to the one in the CdCl₂ alone treatment, and this co-exposure also significantly reduced the Na content when comparing with the NaCl alone treatment. Taken together, our findings suggest that CeO₂ NPs could alleviate the CdCl₂ and NaCl stresses, but could not completely change the phenotype of both contaminants treated rice.

Differential response of Indian mustard (Brassica juncea L., Czern and Coss) under salinity: photosynthetic traits and gene expression

To explore the effect of salt stress on photosynthetic traits and gene expression in Indian mustard, four genotypes CS 54 (national check for salinity), CS 52-SPS-1-2012 (salt tolerant mutant), CS 614-4-1-4-100-13 (salt sensitive mutant) and Pusa bold (high yielding variety) were evaluated under irrigation water salinity (ECiw 12, and 15 dS m-1). Results suggest genotype CS 52-SPS-1-2012 followed by CS 54 performed better under imposed salt stress due to differential regulation of Na+ accumulation in the roots and main stem, restriction of Na+ influx from root to shoot, maintaining higher net photosynthetic traits under saline stress compared to CS 614-4-1-4-100-13 and Pusa bold. Further, overexpression of antiporters (SOS1, SOS2, SOS3, ENH1 and NHX1) and antioxidant (APX1, APX4, DHAR1 and MDHAR) genes in salt tolerant genotypes CS 52-SPS-1-2012 and CS 54 demonstrated their significant role in imparting salt tolerance in Indian mustard.