Salinity Stress Tolerance In Rice Research Articles

Integrative Proteomic and Phosphoproteomic Profiling Reveals the Salt-Responsive Mechanisms in Two Rice Varieties (Oryza Sativa subsp. Japonica and Indica).

Salinity stress induces ionic and osmotic imbalances in rice plants that in turn negatively affect the photosynthesis rate, resulting in growth retardation and yield penalty. Efforts have, therefore, been carried out to understand the mechanism of salt tolerance, however, the complexity of biological processes at proteome levels remains a major challenge. Here, we performed a comparative proteome and phosphoproteome profiling of microsome enriched fractions of salt-tolerant (cv. IR73; indica) and salt-susceptible (cv. Dongjin/DJ; japonica) rice varieties. This approach led to the identification of 5856 proteins, of which 473 and 484 proteins showed differential modulation between DJ and IR73 sample sets, respectively. The phosphoproteome analysis led to the identification of a total of 10,873 phosphopeptides of which 2929 and 3049 phosphopeptides showed significant differences in DJ and IR73 sample sets, respectively. The integration of proteome and phosphoproteome data showed activation of ABA and Ca2+ signaling components exclusively in the salt-tolerant variety IR73 in response to salinity stress. Taken together, our results highlight the changes at proteome and phosphoproteome levels and provide a mechanistic understanding of salinity stress tolerance in rice.

PEPCK Gene for Enhanced Photosynthesis and Salinity Stress Tolerance in Rice: A Review

Phosphoenolpyruvate carboxykinase (PEPCK) is an enzyme of the lyase family utilized in the gluconeogenesis pathway in plants. It converts oxaloacetate into Phosphoenolpyruvate (PEP) and carbon dioxide. PEPCK acts as a prime decarboxylase cytosolic enzyme and may have exhibited a positive response against salinity (main abiotic stress) stress in certain plants. Transgenic plants (C3) with high-level expression of C4 enzymes PEPC or PEPCK can serve as a perfect example for increasing the crop photosynthetic capacity through genetic engineering. In this review, we have focused on the recent advances in the utilization of the PEPCK gene and its role in increasing photosynthesis as well as in abiotic stress tolerance.

Root K+ homeostasis and signalling as a determinant of salinity stress tolerance in cultivated and wild rice species

Cytosolic K+ retention is an important determinant of salinity tolerance in many crops. However, it remains unclear whether this trait is also crucial for wild rice species. In this work, contrasting pairs of cultivated (Oryza sativa L.) and wild (Oryza alta; Oryza punctata) rice species were used to understand the mechanistic basis of salinity stress tolerance in rice and the role of K+ retention in this process. Non-invasive Microelectrode Ion Flux Measuring (MIFE) measurements showed that NaCl and ROS-induced K+ efflux from the elongation root zone were significantly (2–3-fold) higher in the wild rice species compared with their cultivated counterparts. Cultivated rice group showed relatively lower K+ efflux but greater H+ efflux in response to NaCl and ROS treatments. Pharmacological experiments revealed that tetraethylammonium chloride (TEA) and gadolinium chloride (GdCl3) markedly suppressed NaCl and ROS-induced K+ efflux (>80 % inhibition), suggesting the involvement of GORK and NSCC channels in stress-induced K+ efflux. Sodium orthovanadate suppressed H+ efflux (>90 % inhibition), suggesting the role of H+-ATPase as a major source in salt-induced H+ efflux in salt tolerant cultivars. Collectively, our results indicate that, while possessing high root K+ retention ability in the mature zone, wild rice species show higher sensitivity to NaCl and ROS in the elongation zone. It is suggested that stress-induced K+ efflux in this zone may operate as a "metabolic switch" by inhibiting energy consuming anabolic reactions and allowing energy to be saved for adaptations and repairs, which may provide an advantage to wild rice in conditions with high salinity.

Heterologous overexpression of PDH45 gene of pea provides tolerance against sheath blight disease and drought stress in rice

Biotic and abiotic stress tolerant crops are required for sustainable agriculture as well as ensuring global food security. In a previous study, we have reported that heterologous overexpression of pea DNA helicase (PDH45), a DEAD-box family member protein, provides salinity stress tolerance in rice. The improved management of photosynthetic machinery and scavenging of reactive oxygen species (ROS) are associated with PDH45 mediated salinity stress tolerance. However, the role of PDH45 in biotic and other abiotic stress (drought) tolerance remains unexplored. In the present study, we have generated marker-free transgenic IR64 rice lines that overexpress PDH45 under the CaMV35S promoter. The transgenic rice lines exhibited a significant level of tolerance against sheath blight disease, caused by Rhizoctonia solani, a polyphagous necrotrophic fungal pathogen. The defense as well as antioxidant responsive marker genes were significantly upregulated in the PDH45 overexpressing (OE) rice lines, upon pathogen infection. Moreover, the OE lines exhibited tolerance to drought stress and various antioxidant as well as drought responsive marker genes were significantly upregulated in them, upon drought stress. Overall, the current study emphasizes that heterologous overexpression of PDH45 provides abiotic as well as biotic stress tolerance in rice. Tolerance against drought as well as sheath blight disease by overexpression of a single gene (PDH45) signifies the practical implication of the present study. Moreover, considering the conserved nature of the gene in different plant species, we anticipate that PDH45 can be gainfully deployed to impart tolerance against multiple stresses in agriculturally important crops.

Multi-Omics and Integrative Approach towards Understanding Salinity Tolerance in Rice: A Review.

Simple SummaryRice is one of the most significant food crops worldwide, predominantly in Asian countries. Rice plant growth and yield are profoundly affected by salinity stress. Understanding the mechanisms of salinity stress is highly complicated. Therefore, to understand the molecular mechanisms, enhance the yield and development of salinity tolerant cultivars, and achieve spectacular gains in the future, the use of high-throughput frontier technologies must be knotted with a research basis. Keeping these lacunae in mind, this comprehensive review addresses the literature gap and presents the multi-omics and integrative approaches to harnessing the novel avenues of salinity stress mechanisms in rice. Further, this review will be a significant pioneer for researchers working with plant stress biology by employing multi-omics and integrative approaches.Rice (Oryza sativa L.) plants are simultaneously encountered by environmental stressors, most importantly salinity stress. Salinity is the major hurdle that can negatively impact growth and crop yield. Understanding the salt stress and its associated complex trait mechanisms for enhancing salt tolerance in rice plants would ensure future food security. The main aim of this review is to provide insights and impacts of molecular-physiological responses, biochemical alterations, and plant hormonal signal transduction pathways in rice under saline stress. Furthermore, the review highlights the emerging breakthrough in multi-omics and computational biology in identifying the saline stress-responsive candidate genes and transcription factors (TFs). In addition, the review also summarizes the biotechnological tools, genetic engineering, breeding, and agricultural practicing factors that can be implemented to realize the bottlenecks and opportunities to enhance salt tolerance and develop salinity tolerant rice varieties. Future studies pinpointed the augmentation of powerful tools to dissect the salinity stress-related novel players, reveal in-depth mechanisms and ways to incorporate the available literature, and recent advancements to throw more light on salinity responsive transduction pathways in plants. Particularly, this review unravels the whole picture of salinity stress tolerance in rice by expanding knowledge that focuses on molecular aspects.

A novel R3H protein, OsDIP1, confers ABA-mediated adaptation to drought and salinity stress in rice

AimsDehydration responsive element-binding factors (DBFs) have recently emerged as essential components of stress tolerance mechanisms in plants. In this work, we investigated the role of OsDIP1 that operate upstream of DBFs as a regulator of drought and salinity tolerance in rice.MethodsExperiments were conducted on rice plants (Oryza sativa) and included combination of physiological (plant phenotyping) and molecular methods. The latter involved real-time PCR (RT-qPCR); yeast two-hybrid, BiFC assay, GST pull-down, CoIP and firefly luciferase (LUC)/ renilla (REN) assays.ResultsOsDIP1 expression was induced by hydrogen peroxide (H2O2), ABA (abscisic acid), drought (polyethylene glycol treatment), and salt stress. Overexpression of OsDIP1 in rice enhanced drought and salinity tolerance while knocking out OsDIP1 by CRISPR-Cas9 editing resulted in drought and salt sensitive phenotype. The activity and gene expression of antioxidant defense enzymes, superoxide dismutase (SOD), catalase (CAT), was increased in OsDIP1-overexpressed transgenic rice plants, while the content of malondialdehyde (MDA) was decreased. In contrast, the content and gene expression of SODCc2 and CatB, decreased, and the content of MDA was increased in knockout of OsDIP1 rice plants, suggesting that overexpression of OsDIP1 enhances the antioxidant capacity of rice plants. The yeast two-hybrid screening test revealed that OsDIP1 interacted with ZFP36, a key zinc finger transcription factor involved in ABA-induced antioxidant defense. Moreover, OsDIP1 could modulate some key ABA-responsive genes via interacting with ZFP36.ConclusionsIn this work, we show that DIP1 plays a central role in modulating drought and salinity stress tolerance in rice.

Salinity stress tolerance and omics approaches: revisiting the progress and achievements in major cereal crops.

Salinity stress adversely affects plant growth and causes considerable losses in cereal crops. Salinity stress tolerance is a complex phenomenon, imparted by the interaction of compounds involved in various biochemical and physiological processes. Conventional breeding for salt stress tolerance has had limited success. However, the availability of molecular marker-based high-density linkage maps in the last two decades boosted genomics-based quantitative trait loci (QTL) mapping and QTL-seq approaches for fine mapping important major QTL for salinity stress tolerance in rice, wheat, and maize. For example, in rice, 'Saltol' QTL was successfully introgressed for tolerance to salt stress, particularly at the seedling stage. Transcriptomics, proteomics and metabolomics also offer opportunities to decipher and understand the molecular basis of stress tolerance. The use of proteomics and metabolomics-based metabolite markers can serve as an efficient selection tool as a substitute for phenotype-based selection. This review covers the molecular mechanisms for salinity stress tolerance, recent progress in mapping and introgressing major gene/QTL (genomics), transcriptomics, proteomics, and metabolomics in major cereals, viz., rice, wheat and maize.

Association analysis of F2 generation in rice (Oryza sativa L.) under salinity condition

Rice occupies a pivotal place in the Indian agriculture and has been grown under diverse ecological conditions and gets exposed to different environmental stresses like drought, salinity and submergence. Development of rice varieties for salinity affected areas is emphasized on the improvement of rice yield potential in a specific environment. Information related to the relationship between yield and its components in the breeding programme particularly for salinity is very limited. Hence, the present investigation was carried out to study the correlation and path analysis in F2 generation derived from two crosses namely ADT 43 x FL478 (Cross 1) and Improved White Ponni x FL478 (Cross 2) were evaluated at a farmer’s field at Vedapatti village, Tuticorin district of Tamil Nadu which is a saline track. Another rice variety FL478 (IR 66946-3R-178-1-1, derived from crossing between Pokkali and IR 29), has been promoted as an improved donor for breeding programs, as it has a high level of seedling stage salinity tolerance and is photoperiod insensitive, shorter and ûowers earlier than the original Pokkali. FL478 also maintains a lower Na+/K+ ratio than both the parent lines (Gregorio et al. 2002). Based on its ability to tiller well and maintain high potassium content under salinity stress, FL478 appears to be a good candidate for salinity stress tolerance in rice, particularly at the vegetative stage of growth. In Vedapatti village of Tuticorin district, due to over-pumping of groundwater in the past several years, normal irrigation water has become saline water. Moreover, this village is considered as a hot spot area for the saline condition. Hence, the six generations developed through hybridization techniques were evaluated for salinity tolerance at Vedapatti village. The soil and water samples were collected from the field to analyze the EC and pH. The soil salinity and water quality in the experimental plot were 4.82 ECdSm-1 and 8.09 (pH) for soil and 4.78 ECdSm-1 and 8.19 (pH) for water respectively. From the present findings, it is clear that the characters viz., number of tillers per plant, number of productive tillers per plant, number of filled grains per panicle, total number of grains per panicle and spikelet fertility have to be given prime importance during selection since they expressed significant and positive correlation with single plant yield and also a positive inter-correlation among themselves. Therefore, selection for anyone of the above characters would bring in the simultaneous improvement of other traits and also finally resort to improve the grain yield under salinity condition. Path analysis also revealed that selection for the number of productive tillers per plant and the number of filled grains per panicle are to be given prior importance during selection since they had a positive correlation and high direct and indirect effect on grain yield under salinity condition in rice.&nbsp

Tissue-Specific Regulation of Na+ and K+ Transporters Explains Genotypic Differences in Salinity Stress Tolerance in Rice.

Rice (Oryza sativa) is a staple food that feeds more than half the world population. As rice is highly sensitive to soil salinity, current trends in soil salinization threaten global food security. To better understand the mechanistic basis of salinity tolerance in rice, three contrasting rice cultivars—Reiziq (tolerant), Doongara (moderately tolerant), and Koshihikari (sensitive)—were examined and the differences in operation of key ion transporters mediating ionic homeostasis in these genotypes were evaluated. Tolerant varieties had reduced Na+ translocation from roots to shoots. Electrophysiological and quantitative reverse transcription PCR experiments showed that tolerant genotypes possessed 2-fold higher net Na+ efflux capacity in the root elongation zone. Interestingly, this efflux was only partially mediated by the plasma membrane Na+/H+ antiporter (OsSOS1), suggesting involvement of some other exclusion mechanisms. No significant difference in Na+ exclusion from the mature root zones was found between cultivars, and the transcriptional changes in the salt overly sensitive signaling pathway genes in the elongation zone were not correlated with the genetic variability in salinity tolerance amongst genotypes. The most important hallmark of differential salinity tolerance was in the ability of the plant to retain K+ in both root zones. This trait was conferred by at least three complementary mechanisms: (1) its superior ability to activate H+-ATPase pump operation, both at transcriptional and functional levels; (2) reduced sensitivity of K+ efflux channels to reactive oxygen species; and (3) smaller upregulation in OsGORK and higher upregulation of OsAKT1 in tolerant cultivars in response to salt stress. These traits should be targeted in breeding programs aimed to improve salinity tolerance in commercial rice cultivars.

Overexpression of heterotrimeric G protein beta subunit gene (OsRGB1) confers both heat and salinity stress tolerance in rice

Constitutive overexpression of the rice heterotrimeric G protein beta subunit gene (RGB1) in the commercial rice cultivar BRRI Dhan 55 resulted in improved tolerance to heat or salinity or their combination. Two independently in planta transformed plants with the gene confirmed to be integrated at T2 by Southern hybridization and showing high expression at the T3 seedling stage showed better physiological performance after 8 days in 120 mM salt stress than the wild type. The plants had significantly lower electrolyte leakage and malondialdehyde production, while showing higher levels of chlorophyll. Significantly higher germination at 48 °C or with combined stresses of 42/40 °C day/night stress in the presence of 120 mM salt for 2 days was also observed. Stress responsive genes such as OsAPX1, OsSOD, OsHKT1, OsHSP1, OsHSP2 and OsCOR47 showed higher expression in the RGB1 positive plants. These RGB1 transgenic plants can likely provide a strong defense against climate change.

Concurrent overexpression of rice G-protein β and γ subunits provide enhanced tolerance to sheath blight disease and abiotic stress in rice

Our study demonstrates that simultaneous overexpression of RGB1 and RGG1 genes provides multiple stress tolerance in rice by inducing stress responsive genes and better management of ROS scavenging/photosynthetic machineries. The heterotrimeric G-proteins act as signalling molecules and modulate various cellular responses including stress tolerance in eukaryotes. The gamma (γ) subunit of rice G-protein (RGG1) was earlier reported to promote salinity stress tolerance in rice. In the present study, we report that a rice gene-encoding beta (β) subunit of G-protein (RGB1) gets upregulated during both biotic (upon a necrotrophic fungal pathogen, Rhizoctonia solani infection) and drought stresses. Marker-free transgenic IR64 rice lines that simultaneously overexpress both RGB1 and RGG1 genes under CaMV35S promoter were raised. The overexpressing (OE) lines showed enhanced tolerance to R. solani infection and salinity/drought stresses. Several defense marker genes including OsMPK3 were significantly upregulated in the R. solani-infected OE lines. We also found the antioxidant machineries to be upregulated during salinity as well as drought stress in the OE lines. Overall, the present study provides evidence that concurrent overexpression of G-protein subunits (RGG1 and RGB1) impart multiple (both biotic and abiotic) stress tolerance in rice which could be due to the enhanced expression of stress-marker genes and better management of reactive oxygen species (ROS)-scavenging/photosynthetic machinery. The current study suggests an improved approach for simultaneous improvement of biotic and abiotic stress tolerance in rice which remains a major challenge for its sustainable cultivation.

Transcription dynamics of Saltol QTL localized genes encoding transcription factors, reveals their differential regulation in contrasting genotypes of rice.

Salinity is one of the major environmental factors affecting the growth and yield of rice crop. Salinity stress response is a multigenic trait and numerous approaches have been used to dissect out the key determinants of complex salt tolerance trait and their regulation in plant. In the current study, we have investigated expression dynamics of the genes encoding transcription factors (SalTFs) localized within a major salinity tolerance related QTL-'Saltol' in the contrasting cultivars of rice. SalTFs were found to be differentially regulated between the contrasting genotypes of rice, with higher constitutive expression in the salt tolerant landrace, Pokkali than the cultivar IR64. Moreover, SalTFs were found to exhibit inducibility in the salt sensitive cultivar at late duration (after 24h) of salinity stress. Further, the transcript abundance analysis of these SalTFs at various developmental stages of rice revealed that low expressing genes may be involved in developmental responses, while high expressing genes can be linked with the salt stress response. Grouping of these genes was well supported by in silico protein-protein interaction studies and distribution of single-nucleotide polymorphisms (SNPs) and insertions/deletions (InDels) in the promoter and genic regions of these genes. Taken together, we propose that out of 14 SalTFs, eight members are strongly correlated with the salinity stress tolerance in rice and six are involved in plant growth and development.

Improvement of Salinity Stress Tolerance in Rice: Challenges and Opportunities

Rice (Oryza sativa L.) is an important staple crop that feeds more than one half of the world’s population and is the model system for monocotyledonous plants. However, rice is very sensitive to salinity and is the most salt sensitive cereal crop with a threshold of 3 dSm−1 for most cultivated varieties. Despite many attempts using different strategies to improve salinity tolerance in rice, the achievements so far are quite modest. This review aims to discuss challenges that hinder the improvement of salinity stress tolerance in rice as well as potential opportunities for enhancing salinity stress tolerance in this important crop.

Function of heterotrimeric G-protein γ subunit RGG1 in providing salinity stress tolerance in rice by elevating detoxification of ROS.

The present study provides evidence of a unique function of RGG1 in providing salinity stress tolerance in transgenic rice without affecting yield. It also provides a good example for signal transduction from the external environment to inside for enhanced agricultural production that withstands the extreme climatic conditions and ensures food security. The role of heterotrimeric G-proteins functioning as signalling molecules has not been studied as extensively in plants as in animals. Recently, their importance in plant stress signalling has been emerging. In this study, the function of rice G-protein γ subunit (RGG1) in the promotion of salinity tolerance in rice (Oryza sativa L. cv. IR64) was investigated. The overexpression of RGG1 driven by the CaMV35S promoter in transgenic rice conferred high salinity tolerance even in the presence of 200mM NaCl. Transcript levels of antioxidative genes, i.e., CAT, APX, and GR, and their enzyme activities increased in salinity-stressed transgenic rice plants suggesting a better antioxidant system to cope the oxidative-damages caused by salinity stress. The RGG1-induced signalling events that conferred tolerance to salinity was mediated by increased gene expression of the enzymes that scavenged reactive oxygen species. In salinity-stressed RGG1 transgenic lines, the transcript levels of RGG2, RGB, RGA, DEP1, and GS3 also increased in addition to RGG1. These observations suggest that most likely the stoichiometry of the G-protein complex was not disturbed under stress. Agronomic parameters, endogenous sugar content (glucose and fructose) and hormones (GA3, zeatin and IAA) were also higher in the transgenic plants compared with the wild-type plants. A BiFC assay confirmed the interaction of RGG1 with different stress-responsive proteins which play active roles in signalling and prevention of aggregation of proteins under stress-induced perturbation. The present study will help in understanding the G-protein-mediated stress tolerance in plants.

A meta-analysis of potential candidate genes associated with salinity stress tolerance in rice

Even though cultivated rice is highly sensitive to salinity, significant variability exists in the primary and secondary gene-pool of rice with respect to traits of salinity tolerance. Breeding salinity tolerance rice varieties is imperative due to climate change and increasing rice demand for global population. A meta-analysis of plethora of genomic data and published literature available on various genes/factors associated with response to rice salinity and tolerance can be used to enlist selected candidates genes affecting salinity. Such genes can be utilized to identify potential candidate salinity resistance genes from donor rice genotypes and facilitate their transfer to high yielding varieties of rice through marker-assisted breeding. This approach has tremendous advantage over transgenic approach as no bio-safety or regulatory issues are involved in exploiting the variability.Meta-analyses were performed on three datasets viz., rice microarray data of 166 series comprising of 2586 samples, 1228 published research literature in the last one and half decades and RNA-Seq data of 454 and Illumina from Sequence Retrieval Archive (SRA) at NCBI. Among microarray dataset, six salinity related series were finally selected and multi experiment analysis revealed 2289 differentially expressed genes belonging to 44 gene families. Out of these, 13 families viz., AP2-EREBP, AUX/IAA, bZIP, C2H2, bHLH, C3H, HB, HSF, MYB, MYB-related, NAC, Tify and WRKY were selected. Applying various parameters on the published literature data, 13 genes were selected, of which five were common to the different microarray datasets. From RNA-Seq data, total of 751 differentially expressed genes were obtained from 21 gene families, out of which 11 genes were common with those obtained from microarray data and five genes, viz., AP2-EREBP/DREB, MYB, HSF, bZIP and NAC were common to all the three data sets. Based on the results obtained, a total of 31 meta-analyzed genes have been selected and recommended for use in genetic improvement programs aimed at salinity resistance in rice.The meta-analysis of microarray, RNA-Seq and published literature has been successfully used to select 31 best salinity tolerance associated genes which can be exploited by candidate gene approach for targeted introgression through marker assisted breeding. This approach has multi-fold advantages, as it obviates statutory and ecological issues. Such endeavors are more warranted for combating the key abiotic stresses like salinity, whose effects are increasing due to a changing climate.

A computational system biology approach to construct gene regulatory networks for salinity response in rice (Oryza sativa)

Salinity is one of the most common abiotic stress which limits agricultural crop production. Salinity stress tolerance in rice (Oryza sativa L.) is an important trait controlled by various genes. The mechanism of salinity stress response in rice is quite complex. Modelling and construction of genetic regulatory networks is an important tool and can be used for understanding this underlying mechanism. This paper considers the problem of modeling and construction of Gene Regulatory Networks using Multiple Linear Regression and Singular Value Decomposition approach coupled with a number of computational tools. The gene networks constructed by using this approach satisfied the scale free property of biological networks and such networks can be used to extract valuable information on the transcription factors, which are salt responsive. The gene ontology enrichment analysis of selected nodes is performed. The developed model can also be used for predicting the gene responses under stress condition and the result shows that the model fits well for the given gene expression data in rice. In this paper, we have identified ten target genes and a series of potential transcription factors for each target gene in rice which are highly salt responsive.

Genome-wide association mapping of salinity tolerance in rice (Oryza sativa).

Salinity tolerance in rice is highly desirable to sustain production in areas rendered saline due to various reasons. It is a complex quantitative trait having different components, which can be dissected effectively by genome-wide association study (GWAS). Here, we implemented GWAS to identify loci controlling salinity tolerance in rice. A custom-designed array based on 6,000 single nucleotide polymorphisms (SNPs) in as many stress-responsive genes, distributed at an average physical interval of <100 kb on 12 rice chromosomes, was used to genotype 220 rice accessions using Infinium high-throughput assay. Genetic association was analysed with 12 different traits recorded on these accessions under field conditions at reproductive stage. We identified 20 SNPs (loci) significantly associated with Na+/K+ ratio, and 44 SNPs with other traits observed under stress condition. The loci identified for various salinity indices through GWAS explained 5–18% of the phenotypic variance. The region harbouring Saltol, a major quantitative trait loci (QTLs) on chromosome 1 in rice, which is known to control salinity tolerance at seedling stage, was detected as a major association with Na+/K+ ratio measured at reproductive stage in our study. In addition to Saltol, we also found GWAS peaks representing new QTLs on chromosomes 4, 6 and 7. The current association mapping panel contained mostly indica accessions that can serve as source of novel salt tolerance genes and alleles. The gene-based SNP array used in this study was found cost-effective and efficient in unveiling genomic regions/candidate genes regulating salinity stress tolerance in rice.

OsBAT1 Augments Salinity Stress Tolerance by Enhancing Detoxification of ROS and Expression of Stress-Responsive Genes in Transgenic Rice

Coping with salinity-induced reduction in crop yield is essential for food security. Human leukocyte antigen-B associated transcript 1 (BAT1) also called as UAP56 is a DExD/H-box protein involved in messenger RNA (mRNA) splicing. Function of plant homologue of BAT1, especially its involvement in stress tolerance, has not been reported so far. Here, we demonstrate the localization of rice BAT1 (OsBAT1) in the nucleus and in the plasma membrane and its novel function in salinity stress tolerance in rice (Oryza sativa L. cv. IR64). Rice overexpressing OsBAT1 (T1 and T2 generations) show tolerance to high salinity (200 mM NaCl) stress. The T1 transgenics exhibited higher levels of biochemical parameters such as water and chlorophyll contents, net photosynthetic rate, stomatal conductance and intercellular CO2 content as compared to null-segregant (control) plants. The activities of ascorbate peroxidase, guaiacol peroxidase, malondialdehyde and glutathione reductase were significantly higher in transgenics indicating the presence of an efficient antioxidant defence system which helps to cope with salinity-induced oxidative damages. Agronomic parameters were also higher in transgenics as compared to control. Microarray analysis of OsBAT1 overexpressing transgenic lines revealed up-regulation of stress-responsive genes of different pathways including the spliceosome. Our results provide the first direct evidence for a promising function of OsBAT1 in mediating salinity stress response/tolerance in rice.

Pea p68 Imparts Salinity Stress Tolerance in Rice by Scavenging of ROS-Mediated H2O2 and Interacts with Argonaute

The p68, a prototypic member of DEAD-box protein family, is involved in pre-mRNA splicing, RNA-induced silencing and transcription regulation. However, the role of plant p68 in stress tolerance and molecular targets responsible for this has not been reported. Here, we report the isolation and characterization of salinity-induced pea p68 (Psp68). The expression of Psp68 was more in aerial parts as compared to the roots in response to the abiotic stress. The transgenic-overexpressing Psp68 showed enhanced tolerance to salinity stress by efficiently attenuating ionic adjustment and scavenging reactive oxygen species (ROS). The enhanced tolerance was further confirmed by observing several physiological indices. Psp68-overexpressing rice accumulated higher K+ and Ca2+ and lower Na+ level as compared to the wild-type (WT) plants. Furthermore, Psp68 interacts with pea argonaute (AGO1), a catalytic component of the RNA-induced silencing complex (RISC) responsible for the gene silencing. The microarray analysis showed that Psp68 regulates many transcripts involved in the abiotic and oxidative stress responses as well as gene-silencing mechanisms in rice. Thus, the Psp68 functions as a molecular switch in different signaling pathways leading to stress tolerance. Overall, Psp68 may serve as a useful biotechnological tool for the improvement of stress tolerance crops.

Screening for salinity stress tolerance in rice and finger millet genotypes using shoot Na+/K+ ratio and leaf carbohydrate contents as key physiological traits

A study was conducted to find out the genetic variation for salinity tolerance in rice and finger millet genotypes. Twenty finger millet and sixteen rice genotypes were screened for their tolerance/susceptibility against salinity under hydroponics in greenhouse conditions. Screening resulted in the identification of contrasting genotypes in both the crops. Among the rice genotypes, IR 29 was found to be susceptible and FL 478 was found to be tolerant to salinity stress. Among the finger millet genotypes, CO 12 was susceptible and Trichy 1 was tolerant to salinity stress. Two genotypes showing contrasting behavior to salt stress were analyzed for their shoot Na+ to K+ ratio and leaf carbohydrate contents to understand the physiological basis of salinity tolerance. In rice and finger millet, the shoot Na+/K+ ratio was found to be significantly lower, and the carbohydrate contents were much higher in the tolerant FL 478 and Trichy 1 relative to IR29 and CO 12 upon salinity treatment. Lower shoot Na+/K+ ratio coupled with higher carbohydrate contents could serve as indices to screen genotypes tolerant to salinity stresses.