Pea DNA helicase 45 overexpression in tobacco confers high salinity tolerance without affecting yield

Total Synthesis of Strigolactones via Palladium-Catalyzed Cascade Carbonylative Carbocyclization of Enallenes

Here we report an efficient route for synthesizing strigolactones (SLs) and their derivatives. Our method relies on a palladium-catalyzed oxidative carbonylation/carbocyclization/carbonylation/alkoxylation cascade reaction, which involves the formation of three new C-C bonds and a new C-O bond while cleaving one C(sp3)-H bond in a single step. With our versatile synthetic strategy, both naturally occurring and artificial SLs were prepared.

The impact of multiple abiotic stresses on ns-LTP2.8 gene transcript and ns-LTP2.8 protein accumulation in germinating barley (Hordeum vulgare L.) embryos

Abiotic stresses occur more often in combination than alone under regular field conditions limiting in more severe way crop production. Stress recognition in plants primarily occurs in the plasma membrane, modification of which is necessary to maintain homeostasis in response to it. It is known that lipid transport proteins (ns-LTPs) participate in modification of the lipidome of cell membranes. Representative of this group, ns-LTP2.8, may be involved in the reaction to abiotic stress of germinating barley plants by mediating the intracellular transport of hydrophobic particles, such as lipids, helping to maintain homeostasis. The ns-LTP2.8 protein was selected for analysis due to its ability to transport not only linear hydrophobic molecules but also compounds with a more complex spatial structure. Moreover, ns-LTP2.8 has been qualified as a member of pathogenesis-related proteins, which makes it particularly important in relation to its high allergenic potential. This paper demonstrates for the first time the influence of various abiotic stresses acting separately as well as in their combinations on the change in the ns-LTP2.8 transcript, ns-LTP2.8 protein and total soluble protein content in the embryonal axes of germinating spring barley genotypes with different ns-LTP2.8 allelic forms and stress tolerance. Tissue localization of ns-LTP2.8 transcript as well as ns-LTP2.8 protein were also examined. Although the impact of abiotic stresses on the regulation of gene transcription and translation processes remains not fully recognized, in this work we managed to demonstrate different impact on applied stresses on the fundamental cellular processes in very little studied tissue of the embryonal axis of barley.

Phenotypic and microarray analysis reveals salinity stress-induced oxidative tolerance in transgenic rice expressing a DEAD-box RNA helicase, OsDB10

Helicases are the motor proteins not only involved in the process of mRNA metabolism but also played a significant role in providing abiotic stresses tolerance. In this study, a DEAD-box RNA helicase OsDB10 was cloned and functionally characterized. The transcript levels of OsDB10 were increased both in shoot and root upon salt, heat, cold, and ABA application and was more prominent in shoot compared to root. Genomic integration of OsDB10 in transgenic rice was confirmed by PCR, Southern blot and qRT-PCR analysis. The transgenic plants showed quicker seed germination, reduced necrosis, higher chlorophyll, more survival rate, better seedling growth, and produced more grain yield under salinity stress. Furthermore, transgenic lines also accumulated less Na+ and high K+ ions and salinity tolerance of the transgenic were also assayed by measuring different bio-physiological indices. Moreover, the OsDB10 transgenic plants showed enhanced tolerance to salinity-induced oxidative stress by scavenging ROS and increased activity of antioxidants enzymes. Microarray analysis showed upregulation of transcriptional regulations and metabolic reprogramming as OsDB10 overexpression modulates the expression of many other genes. Altogether, our results confirmed that OsDB10 is a functional DEAD-box RNA helicase and played vital roles in plant defence response against salinity stress.

Strigolactones can be a potential tool to fight environmental stresses in arid lands

BACKGROUND

Environmental stresses pose a significant threat to plant growth and ecosystem productivity, particularly in arid lands that are more susceptible to climate change. Strigolactones (SLs), carotenoid-derived plant hormones, have emerged as a potential tool for mitigating environmental stresses.

METHODS

This review aimed to gather information on SLs' role in enhancing plant tolerance to ecological stresses and their possible use in improving the resistance mechanisms of arid land plant species to intense aridity in the face of climate change.

RESULTS

Roots exude SLs under different environmental stresses, including macronutrient deficiency, especially phosphorus (P), which facilitates a symbiotic association with arbuscular mycorrhiza fungi (AMF). SLs, in association with AMF, improve root system architecture, nutrient acquisition, water uptake, stomatal conductance, antioxidant mechanisms, morphological traits, and overall stress tolerance in plants. Transcriptomic analysis revealed that SL-mediated acclimatization to abiotic stresses involves multiple hormonal pathways, including abscisic acid (ABA), cytokinins (CK), gibberellic acid (GA), and auxin. However, most of the experiments have been conducted on crops, and little attention has been paid to the dominant vegetation in arid lands that plays a crucial role in reducing soil erosion, desertification, and land degradation. All the environmental gradients (nutrient starvation, drought, salinity, and temperature) that trigger SL biosynthesis/exudation prevail in arid regions. The above-mentioned functions of SLs can potentially be used to improve vegetation restoration and sustainable agriculture.

CONCLUSIONS

Present review concluded that knowledge on SL-mediated tolerance in plants is developed, but still in-depth research is needed on downstream signaling components in plants, SL molecular mechanisms and physiological interactions, efficient methods of synthetic SLs production, and their effective application in field conditions. This review also invites researchers to explore the possible application of SLs in improving the survival rate of indigenous vegetation in arid lands, which can potentially help combat land degradation problems.

Functional genomic analysis of K+ related salt-responsive transporters in tolerant and sensitive genotypes of rice

INTRODUCTION

Salinity is a complex environmental stress that affects the growth and production of rice worldwide. But there are some rice landraces in coastal regions that can survive in presence of highly saline conditions. An understanding of the molecular attributes contributing to the salinity tolerance of these genotypes is important for developing salt-tolerant high yielding modern genotypes to ensure food security. Therefore, we investigated the role and functional differences of two K⁺ salt-responsive transporters. These are OsTPKa or Vacuolar two-pore potassium channel and OsHAK_like or a hypothetical protein of the HAK family. These transporters were selected from previously identified QTLs from the tolerant rice landrace genotype (Horkuch) and sensitive genotype (IR29).

METHODS

In silico comparative sequence analysis of the promoter sequences of two these genes between Horkuch and IR29 was done. Real-Time expression of the selected genes in leaves and roots of IR29 (salt-sensitive), I-14 and I-71 (Recombinant Inbred Lines of IR29(♀)× Horkuch), Horkuch and Pokkali (salt-tolerant) under salt-stress at different time points was analyzed. For further insight, OsTPKa and OsHAK_like were chosen for loss-of-function genomic analysis in Horkuch using the CRISPR/Cas9 tool. Furthermore, OsTPKa was chosen for cloning into a sensitive variety by Gateway technology to observe the effect of gain-of-function.

RESULTS

The promoter sequences of the OsTPKa and OsHAK_like genes showed some significant differences in promoter sequences which may give a survival advantage to Horkuch under salt-stress. These two genes were also found to be overexpressed in tolerant varieties (Horkuch and Pokkali). Moreover, a coordinated expression pattern between these two genes was observed in tolerant Horkuch under salt-stress. Independently transformed plants where the expression of these genes was significantly lowered, performed poorly in physiological tests for salinity tolerance. On the other hand, positively transformed T₀ plants with the OsTPKa gene from Horkuch consistently showed growth advantage under both control and salt stress.

DISCUSSION

The poor performance of the transgenic plants with the down-regulated genes OsTPKa and OsHAK_like under salt stress supports the assumption that OsTPKa and OsHAK_like play important roles in defending the rice landrace Horkuch against salt stress, minimizing salt injury, and maintaining plant growth. Moreover, the growth advantage provided by overexpression of the vacuolar OsTPKa K⁺ transporter, particularly under salt stress reconfirms its important role in providing salt tolerance. The QTL locus from Horkuch containing these two transporters maybe bred into commercial rice to produce high-yielding salt tolerant rice.

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.

Quantitative phosphoproteomics reveals the role of wild soybean GsSnRK1 as a metabolic regulator under drought and alkali stresses

Drought and alkali stresses cause detrimental effects on plant growth and development. SnRK1 protein kinases act as key energy and stress sensors by phosphorylation-mediated signaling in the regulation of plant defense reactions against adverse environments. To understand SnRK1-dependent phosphorylation events in signaling pathways triggered by abiotic factors, we employed quantitative phosphoproteomics to compare the global changes in phosphopeptides and phosphoproteins in 2kinm mutant Arabidopsis (SnRK1.1 T-DNA knockout and SnRK1.2 knockdown by β-estradiol-induced RNAi) complemented with wild soybean GsSnRK1(wt) or dominant negative mutant GsSnRK1(K49M) in response to drought and alkali stresses. Among 4014 phosphopeptides (representing 2380 phosphoproteins) identified in this study, we finalized 74 phosphopeptides (representing 61 phosphoproteins), and 75 phosphopeptides (representing 57 phosphoproteins) showing significant changes in phosphorylation levels under drought and alkali treatments respectively. Function enrichment and protein-protein interaction analyses indicated that the differentially-expressed phosphoproteins (DPs) under drought and alkali stresses were mainly involved in signaling transduction, stress response, carbohydrate and energy metabolism, transport and membrane trafficking, RNA splicing and processing, DNA binding and gene expression, and protein synthesis/folding/degradation. These results provide assistance to identify bona fide and novel SnRK1 phosphorylation substrates and shed new light on the biological functions of SnRK1 kinase in responses to abiotic stresses. SIGNIFICANCE: These results provide assistance to identify novel SnRK1 phosphorylation substrates and regulatory proteins, and shed new light on investigating the potential roles of reversible phosphorylation in plant responses to abiotic stresses.

Marker-Free Rice (Oryza sativa L. cv. IR 64) Overexpressing PDH45 Gene Confers Salinity Tolerance by Maintaining Photosynthesis and Antioxidant Machinery

Helicases function as key enzymes in salinity stress tolerance, and the role and function of PDH45 (pea DNA helicase 45) in stress tolerance have been reported in different crops with selectable markers, raising public and regulatory concerns. In the present study, we developed five lines of marker-free PDH45-overexpressing transgenic lines of rice (Oryza sativa L. cv. IR64). The overexpression of PDH45 driven by CaMV35S promoter in transgenic rice conferred high salinity (200 mM NaCl) tolerance in the T1 generation. Molecular attributes such as PCR, RT-PCR, and Southern and Western blot analyses confirmed stable integration and expression of the PDH45 gene in the PDH45-overexpressing lines. We observed higher endogenous levels of sugars (glucose and fructose) and hormones (GA, zeatin, and IAA) in the transgenic lines in comparison to control plants (empty vector (VC) and wild type (WT)) under salt treatments. Furthermore, photosynthetic characteristics such as net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 (Ci), and chlorophyll (Chl) content were significantly higher in transgenic lines under salinity stress as compared to control plants. However, the maximum primary photochemical efficiency of PSII, as an estimated from variable to maximum chlorophyll a fluorescence (Fv/Fm), was identical in the transgenics to that in the control plants. The activities of antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (GPX), were significantly higher in transgenic lines in comparison to control plants, which helped in keeping the oxidative stress burden (MDA and H2O2) lesser on transgenic lines, thus protecting the growth and photosynthetic efficiency of the plants. Overall, the present research reports the development of marker-free PDH45-overexpressing transgenic lines for salt tolerance that can potentially avoid public and biosafety concerns and facilitate the commercialization of genetically engineered crop plants.

Physiological and transcriptomic analyses reveal novel insights into the cultivar-specific response to alkaline stress in alfalfa (Medicago sativa L.)

Soil alkalization severely limits plant growth and development, however, the mechanisms of alkaline response in plants remain largely unknown. In this study, we performed physiological and transcriptomic analyses using two alfalfa cultivars (Medicago sativa L.) with different sensitivities to alkaline conditions. The chlorophyll content and shoot fresh mass drastically declined in the alkaline-sensitive cultivar Algonquin (AG) following alkaline treatment (0-25 mM Na2CO3 solution), while the alkaline-tolerant cultivar Gongnong NO.1 (GN) maintained relatively stable growth and chlorophyll content. Compared with AG, GN had higher contents of Ca2+ and Mg2+; the ratios of Ca2+ and Mg2+ to Na+, proline and soluble sugar, as well as higher enzyme activities of peroxidase (POD) and catalase (CAT) under the alkaline conditions. Furthermore, transcriptomic analysis identified three categories of alkaline-responsive differentially expressed genes (DEGs) between the two cultivars: 48 genes commonly induced in both the cultivars (CAR), 574 genes from the tolerant cultivar (TAR), and 493 genes from the sensitive cultivar (SAR). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that CAR genes were mostly involved in phenylpropanoid biosynthesis, lipid metabolism, and DNA replication and repair; TAR genes were significantly enriched in metabolic pathways, such as biosynthesis of amino acids and secondary metabolites including flavonoids, and the MAPK signaling pathway; SAR genes were specifically enriched in vitamin B6 metabolism. Taken together, the results identified candidate pathways associated with genetic variation in response to alkaline stress, providing novel insights into the mechanisms underlying alkaline tolerance in alfalfa.

Production of Betacyanins in Transgenic Nicotiana tabacum Increases Tolerance to Salinity

Although red betalain pigments (betacyanins) have been associated with salinity tolerance in some halophytes like Disphyma australe, efforts to determine whether they have a causal role and the underlying mechanisms have been hampered by a lack of a model system. To address this, we engineered betalain-producing Nicotiana tabacum, by the introduction of three betalain biosynthetic genes. The plants were violet-red due to the accumulation of three betacyanins: betanin, isobetanin, and betanidin. Under salt stress, betacyanic seedlings had increased survivability and leaves of mature plants had higher photochemical quantum yields of photosystem II (F _v /F _m ) and faster photosynthetic recovery after saturating light treatment. Under salt stress, compared to controls betacyanic leaf disks had no loss of carotenoids, a slower rate of chlorophyll degradation, and higher F _v /F _m values. Furthermore, simulation of betacyanin pigmentation by using a red filter cover improved F _v /F _m value of green tissue under salt stress. Our results confirm a direct causal role of betacyanins in plant salinity tolerance and indicate a key mechanism is photoprotection. A role in delaying leaf senescence was also indicated, and the enhanced antioxidant capability of the betacyanic leaves suggested a potential contribution to scavenging reactive oxygen species. The study can inform the development of novel biotechnological approaches to improving agricultural productivity in saline-affected areas.

The DEAD-box RNA helicase eIF4A1 interacts with the SWI2/SNF2-related chromatin remodelling ATPase DDM1 in the moss Physcomitrella

eIF4A is a DEAD box containing RNA helicase that plays crucial roles in regulating translation initiation, growth and abiotic stress tolerance in plants. It also functions as an ATP-dependent RNA binding protein to curb granule formation by limiting RNA-RNA interactions that promote RNA condensation and formation of ribonucleoprotein particles in vivo. Helicase activity of eIF4A is known to be dictated by its binding partners. Proteins interacting with eIF4A have been identified across land plants. In monocots a close link between eIF4A regulated processes and DNA methylation in epigenetic regulation of plant development is inferred from interaction between OseIF4A and the de novo methyltransferase OsDRM2 and loss-of-function studies of these genes in Oryza sativa and Brachypodium distachyon. In the moss Physcomitrella patens, eIF4A1 encoded by Pp3c6_1080V3.1 interacts with the heterogeneous nuclear ribonucleoprotein (hnRNP) PpLIF2L1, homolog of which in Arabidopsis regulates transcription of stress-responsive genes. In this study, using different protein-protein interaction methods, targeted gene knockout strategy and quantitative expression analysis we show genetic interaction between PpeIF4A1 and the putative nucleosome remodeler protein PpDDM1 and between PpDDM1 and PpLIF2L1 in vivo. Stress-induced co-expression of PpeIF4A1, PpDDM1 and PpLIF2L1, their roles in salt stress tolerance and differences in subnuclear distribution of PpLIF2L1 in ppeif4a1 cells in comparison to wild type suggest existence of a regulatory network comprising of RNA helicases, chromatin remodelling proteins and hnRNP active in stress-responsive biological processes in P. patens.

Ectopic expression of nucleolar DEAD-Box RNA helicase OsTOGR1 confers improved heat stress tolerance in transgenic Chinese cabbage

The DEAD-Box RNA helicase OsTOGR1 positively regulates heat stress tolerance in Chinese cabbage. Non-heading Chinese cabbage (Brassica rapa L. ssp. chinensis) is primarily cultivated vegetable crop in Asian countries. Heat stress is one of the major threats for its growth and yield. Numerous regulatory genes in various crops have shown to contribute thermotolerance. Among them, Thermotolerant growth required 1 (TOGR1) is an important DEAD-box RNA helicase. To examine whether its role is conserved in other crops, we constructed pCAMBIA1300-pHSP:OsTOGR1 expression vector driven by the rice small heat shock protein promoter (pHSP17.9) and successfully produced transgenic non-heading Chinese cabbage plants expressing OsTOGR1 gene via Agrobacterium-mediated vacuum infiltration transformation. In total, we generated three independent transgenic cabbage lines expressing TOGR1 gene. Expression and integration of TOGR1 was confirmed by PCR, RT-PCR and qPCR in T₁ and T₂ generations. The relative leaf electrical conductivity of transgenic seedlings was reduced subjected to high temperature (38 °C) compared to heat shock treatment (46 °C). In addition, hypocotyl length of transgenic seedlings increased compared to wild-type plants under high temperature and heat shock treatment. Furthermore, the transgenic plants exhibited higher chlorophyll content than wild-type plants under high temperature and heat shock treatment. The transgenic seeds displayed better germination under heat shock treatment. Tested heat stress-responsive genes were also up-regulated in the transgenic plants subjected to high temperature or heat shock treatment. To the best of our knowledge, this is the first report on describing the role of DAED-Box RNA helicases in improving heat stress tolerance of transgenic plants.

Understanding the thermal response of rice eukaryotic transcription factor eIF4A1 towards dynamic temperature stress: insights from expression profiling and molecular dynamics simulation

Eukaryotic translation initiation factors (eIFs) are the group of regulatory proteins that are involved in the initiation of translation events. Among them, eIF4A1, a member of the DEAD-box RNA helicase family, participates in a wide spectrum of activities which include, RNA splicing, ribosome biogenesis, and RNA degradation. It is well known that ATP-binding and subsequent hydrolysis activities are crucial for the functionality of such helicases. Although the stress-responsive upregulation of eIF4A1 has been reported in plants during stress, it is difficult to anticipate the functionality of the corresponding protein product. Therefore, to understand the activity of eIF4A1 in rice in response to temperature stress, we first conducted an expression analysis of the gene and further investigated the structural stability of the eIF4A1-ATP/Mg²⁺ complex through molecular dynamics (MD) simulations at different temperature conditions (277 K, 300 K, and 315 K). Our results demonstrated a three to fourfold increased expression of rice eIF4A1 both in root and shoot at 42 °C compared to control. Furthermore, the MD simulation portrayed strong ATP/Mg²⁺ binding at a higher temperature in comparison to control and cold temperature. Overall, the increased expression pattern of eIF4A1 and strong ATP/Mg²⁺ binding at higher temperature indicated the heat stress-tolerant capacity of the gene in rice. The results from our study will help in understanding the activity of gene and guide the researchers for screening of novel stress inducible candidate genes for the engineering of temperature stress tolerant plants.Communicated by Ramaswamy H. Sarma.

Proteomics Revealed Distinct Responses to Salinity between the Halophytes Suaeda maritima (L.) Dumort and Salicornia brachiata (Roxb)

Plant resistance to salinity stress is one of the main challenges of agriculture. The comprehension of the molecular and cellular mechanisms involved in plant tolerance to salinity can help to contrast crop losses due to high salt conditions in soil. In this study, Salicornia brachiata and Suaeda maritima, two plants with capacity to adapt to high salinity levels, were investigated at proteome level to highlight the key processes involved in their tolerance to NaCl. With this purpose, plants were treated with 200 mM NaCl as optimal concentration and 500 mM NaCl as a moderate stressing concentration for 14 days. Indeed, 200 mM NaCl did not result in an evident stress condition for both species, although photosynthesis was affected (with a general up accumulation of photosynthesis-related proteins in S. brachiata under salinity). Our findings indicate a coordinated response to salinity in both the halophytes considered, under NaCl conditions. In addition to photosynthesis, heat shock proteins and peroxidase, expansins, signaling processes, and modulation of transcription/translation were affected by salinity. Interestingly, our results suggested distinct mechanisms of tolerance to salinity between the two species considered, with S. brachiata likely having a more efficient mechanism of response to NaCl.

Physiological and Transcriptome Analysis of Sugar Beet Reveals Different Mechanisms of Response to Neutral Salt and Alkaline Salt Stresses

The salinization and alkalization of soil are widespread environmental problems. Sugar beet (B. vulgaris L.) is a moderately salt tolerant glycophyte, but little is known about the different mechanisms of sugar beet response to salt and alkaline stresses. The aim of this study was to investigate the influence of neutral salt (NaCl:Na₂SO₄, 1:1) and alkaline salt (Na₂CO₃) treatment on physiological and transcriptome changes in sugar beet. We found that a low level of neutral salt (NaCl:Na₂SO₄; 1:1, Na⁺ 25 mM) or alkaline salt (Na₂CO₃, Na⁺ 25 mM) significantly enhanced total biomass, leaf area and photosynthesis indictors in sugar beet. Under a high concentration of alkaline salt (Na₂CO₃, Na⁺ 100 mM), the growth of plants was not significantly affected compared with the control. But a high level of neutral salt (NaCl: Na₂SO₄; 1:1, Na⁺ 100 mM) significantly inhibited plant growth and photosynthesis. Furthermore, sugar beet tends to synthesize higher levels of soluble sugar and reducing sugar to cope with high neutral salt stress, and more drastic changes in indole acetic acid (IAA) and abscisic acid (ABA) contents were detected. We used next-generation RNA-Seq technique to analyze transcriptional changes under neutral salt and alkaline salt treatment in sugar beet. Overall, 4,773 and 2,251 differentially expressed genes (DEGs) were identified in leaves and roots, respectively. Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that genes involving cutin, suberine and wax biosynthesis, sesquiterpenoid and triterpenoid biosynthesis and flavonoid biosynthesis had simultaneously changed expression under low neutral salt or alkaline salt, so these genes may be related to stimulating sugar beet growth in both low salt treatments. Genes enriched in monoterpenoid biosynthesis, amino acids metabolism and starch and sucrose metabolism were specifically regulated to respond to the high alkaline salt. Meanwhile, compared with high alkaline salt, high neutral salt induced the expression change of genes involved in DNA replication, and decreased the expression of genes participating in cutin, suberine and wax biosynthesis, and linoleic acid metabolism. These results indicate the presence of different mechanisms responsible for sugar beet responses to neutral salt and alkaline salt stresses.

The DEAD-box RNA helicase eIF4A regulates plant development and interacts with the hnRNP LIF2L1 in Physcomitrella patens

eIF4A is a RNA-stimulated ATPase and helicase. Besides its key role in regulating cap-dependent translation initiation in eukaryotes, it also performs specific functions in regulating cell cycle progression, plant growth and abiotic stress tolerance. Flowering plants encode three eIF4A paralogues, eIF4A1, eIF4A2 and eIF4A3 that share conserved sequence motifs but differ in functions. To date, however, no information is available on eIF4A in basal land plants. In this study we report that genome of the moss Physcomitrella patens encodes multiple eIF4A genes. The encoded proteins possess the highly conserved motifs characteristic of the DEAD box helicases. Spatial expression analysis shows these genes to be ubiquitously expressed in all tissue types with Pp3c6_1080V3.1 showing high expression in filamentous protonemata. Targeted deletion of conserved core motifs in Pp3c6_1080V3.1 slowed protonemata growth and resulted in dwarfing of leafy gametophores suggesting a role for Pp3c6_1080V3.1 in regulating cell division/elongation. Rapid and strong induction of Pp3c6_1080V3.1 under salt stress and slow recovery of knockout plants upon exposure to high salt further suggest Pp3c6_1080V3.1 to be involved in stress management in P. patens. Protein-protein interaction studies that show Pp3c6_1080V3.1 to interact with the Physcomitrella heterogenous ribonucleoprotein, LIF2L1, a transcriptional regulator of stress-responsive genes in Arabidopsis. The results presented in this study provide insight into evolutionary conserved functions of eIF4A and shed light on the novel link between eIF4A activities and stress mitigation pathways/RNA metabolic processes in P. patens.

NHX1 and eIF4A1-stacked transgenic sweetpotato shows enhanced tolerance to drought stress

Co-expression of Na⁺/H⁺ antiporter NHX1 and DEAD-box RNA helicase eIF4A1 from Arabidopsis positively regulates drought stress tolerance by improving ROS scavenging capacity and maintaining membrane integrity in sweetpotato. Plants evolve multiple strategies for stress adaptation in nature. To improve sweetpotato resistance to drought stress, transgenic sweetpotato plants overexpressing the Arabidopsis Na⁺/H⁺ antiporter, NHX1, and the translation initiation factor elF4A1 were characterized for phenotypic traits and physiological performance. Without drought treatment, the NHX1-elF4A1 stacked lines (NE lines) showed normal, vigorous growth comparable to the WT plants. The NE plants showed dense green foliage with delayed leaf senescence and developed more roots than WT plants under drought treatment for 18 days. Compared to WT plants, higher level of reactive oxygen scavenging capacity was detected in NE lines as indicated by reduced H₂O₂ accumulation as well as increased superoxide dismutase activity and proline content. The relative ion leakage and malondialdehyde content were reduced in NE plants, indicating improved maintenance of intact membranes system. Both NE plants and NHX1-overexpressing plants (N lines) showed larger aerial parts and well-developed root system compared to WT plants under the drought stress conditions, likely due to the improved antioxidant capacity. The NE plants showed better ROS scavenging than N-line plants. All N- and NE-line plants produced normal storage roots with similar yields as WT in the field under normal growth conditions. These results demonstrated the potential to enhance sweetpotato productivity through stacking genes that are involved in ion compartmentalization and translation initiation.

Association mapping of a locus that confers southern stem canker resistance in soybean and SNP marker development

BACKGROUND

Southern stem canker (SSC), caused by Diaporthe aspalathi (E. Jansen, Castl. & Crous), is an important soybean disease that has been responsible for severe losses in the past. The main strategy for controlling this fungus involves the introgression of resistance genes. Thus far, five main loci have been associated with resistance to SSC. However, there is a lack of information about useful allelic variation at these loci. In this work, a genome-wide association study (GWAS) was performed to identify allelic variation associated with resistance against Diaporthe aspalathi and to provide molecular markers that will be useful in breeding programs.

RESULTS

We characterized the response to SSC infection in a panel of 295 accessions from different regions of the world, including important Brazilian elite cultivars. Using a GBS approach, the panel was genotyped, and we identified marker loci associated with Diaporthe aspalathi resistance through GWAS. We identified 19 SNPs associated with southern stem canker resistance, all on chromosome 14. The peak SNP showed an extremely high degree of association (p-value = 6.35E-27) and explained a large amount of the observed phenotypic variance (R2 = 70%). This strongly suggests that a single major gene is responsible for resistance to D. aspalathi in most of the lines constituting this panel. In resequenced soybean materials, we identified other SNPs in the region identified through GWAS in the same LD block that clearly differentiate resistant and susceptible accessions. The peak SNP was selected and used to develop a cost-effective molecular marker assay, which was validated in a subset of the initial panel. In an accuracy test, this SNP assay demonstrated 98% selection efficiency.

CONCLUSIONS

Our results suggest relevance of this locus to SSC resistance in soybean cultivars and accessions from different countries, and the SNP marker assay developed in this study can be directly applied in MAS studies in breeding programs to select materials that are resistant against this pathogen and support its introgression.

Morphophysiological and molecular evidence supporting the augmentative role of Piriformospora indica in mitigation of salinity in Cucumis melo L

Salinity is one of the major limiting factors in plant growth and productivity. Cucumis melo L. is a widely cultivated plant, but its productivity is significantly influenced by the level of salinity in soil. Symbiotic colonization of plants with Piriformospora indica has shown a promotion in plants growth and tolerance against biotic stress. In this study, physiological markers such as ion analysis, antioxidant determination, proline content, electrolyte leakage and chlorophyll measurement were assessed in melon cultivar under two concentrations (100 and 200 mM) of NaCl with and without P. indica inoculation. Results showed that the endophytic inoculation consistently upregulated the level of antioxidants, enhanced plants to antagonize salinity stress. The expression level of an RNA editing factor (SLO2) which is known to participate in mitochondria electron transport chain was analyzed, and its full mRNA sequence was obtained by rapid amplification of cDNA ends (RACE). Under salinity stress, the expression level of SLO2 was increased, enhancing the plant's capability to adapt to the stress. However, P. indica inoculation further elevated the expression level of SLO2. These findings suggested that the symbiotic association of fungi could help the plants to tolerate the salinity stress.

Pea p68, a DEAD-box helicase, enhances salt tolerance in marker-free transgenic plants of soybean [Glycine max (L.) Merrill]

Protein p68 is a prototype constituent of DEAD-box protein family, which is involved in RNA metabolism, induced during abiotic stress conditions. In order to address the salinity stress faced by economically important soybean crop, we have transformed soybean cv. PUSA 9712 via direct organogenesis with marker free construct of p68 gene by Agrobacterium-mediated genetic transformation. The putative transgenic plants were screened by Polymerase chain reaction (PCR), Dot blot analysis and Southern blot hybridization. Reverse transcriptase-PCR (RT-PCR) and Quantitative real-time PCR (qRT-PCR) established that the p68 gene expressed in three out of five southern positive (T1) plants. The transformed (T1) soybean plants survived irrigation upto 200 mM of NaCl whereas the non-transformed (NT) plants could not survive even 150 mM NaCl. The transgenic soybean (T1) plants showed a higher accumulation of chlorophyll, proline, CAT, APX, SOD, RWC, DHAR and MDHAR than the NT plants under salinity stress conditions. The transformed (T1) soybean plants also retained a higher net photosynthetic rate, stomatal conductance and CO2 assimilation as compared to NT plants. Further analysis revealed that (T1) soybean plants accumulated higher K+ and lower Na+ levels than NT plants. Yield performance of transformed soybean plants was estimated in the transgenic green house under salinity stress conditions. The transformed (T1) soybean plants expressing the p68 gene were morphologically similar to non-transformed plants and produced 22-24 soybean pods/plant containing 8-9 g (dry weight) of seeds at 200 mM NaCl concentration. The present investigation evidenced the role of the p68 gene against salinity, by enhancing the tolerance towards salinity stress in soybean plants.

Overexpression of the DEAD-Box RNA Helicase Gene AtRH17 Confers Tolerance to Salt Stress in Arabidopsis

Plants adapt to abiotic stresses by complex mechanisms involving various stress-responsive genes. Here, we identified a DEAD-box RNA helicase (RH) gene, AtRH17, in Arabidopsis, involved in salt-stress responses using activation tagging, a useful technique for isolating novel stress-responsive genes. AT895, an activation tagging line, was more tolerant than wild type (WT) under NaCl treatment during germination and seedling development, and AtRH17 was activated in AT895. AtRH17 possesses nine well-conserved motifs of DEAD-box RHs, consisting of motifs Q, I, Ia, Ib, and II-VI. Although at least 12 orthologs of AtRH17 have been found in various plant species, no paralog occurs in Arabidopsis. AtRH17 protein is subcellularily localized in the nucleus. AtRH17-overexpressing transgenic plants (OXs) were more tolerant to high concentrations of NaCl and LiCl compared with WT, but no differences from WT were detected among seedlings exposed to mannitol and freezing treatments. Moreover, in the mature plant stage, AtRH17 OXs were also more tolerant to NaCl than WT, but not to drought, suggesting that AtRH17 is involved specifically in the salt-stress response. Notably, transcriptions of well-known abscisic acid (ABA)-dependent and ABA-independent stress-response genes were similar or lower in AtRH17 OXs than WT under salt-stress treatments. Taken together, our findings suggest that AtRH17, a nuclear DEAD-box RH protein, is involved in salt-stress tolerance, and that its overexpression confers salt-stress tolerance via a pathway other than the well-known ABA-dependent and ABA-independent pathways.

Gene encoding vesicle-associated membrane protein-associated protein from Triticum aestivum (TaVAP) confers tolerance to drought stress

Abiotic stresses like drought, salinity, high and low temperature, and submergence are major factors that limit the crop productivity. Hence, identification of genes associated with stress response in crops is a prerequisite for improving their tolerance to adverse environmental conditions. In an earlier study, we had identified a drought-inducible gene, vesicle-associated membrane protein-associated protein (TaVAP), in developing grains of wheat. In this study, we demonstrate that TaVAP is able to complement yeast and Arabidopsis mutants, which are impaired in their respective orthologs, signifying functional conservation. Constitutive expression of TaVAP in Arabidopsis imparted tolerance to water stress conditions without any apparent yield penalty. Enhanced tolerance to water stress was associated with maintenance of higher relative water content, photosynthetic efficiency, and antioxidant activities. Compared to wild type, the TaVAP-overexpressing plants showed enhanced lateral root proliferation that was attributed to higher endogenous levels of IAA. These studies are the first to demonstrate that TaVAP plays a critical role in growth and development in plants, and is a potential candidate for improving the abiotic stress tolerance in crop plants.

Stress-induced Oryza sativa RuvBL1a is DNA-independent ATPase and unwinds DNA duplex in 3' to 5' direction

RuvB, a member of AAA+ (ATPases Associated with diverse cellular Activities) superfamily of proteins, is essential, highly conserved and multifunctional in nature as it is involved in DNA damage repair, mitotic assembly, switching of histone variants and assembly of telomerase core complex. RuvB family is widely studied in various systems such as Escherichia coli, yeast, human, Drosophila, Plasmodium falciparum and mouse, but not well studied in plants. We have studied the transcript level of rice homologue of RuvB gene (OsRuvBL1a) under various abiotic stress conditions, and the results suggest that it is upregulated under salinity, cold and heat stress. Therefore, the OsRuvBL1a protein was characterized using in silico and biochemical approaches. In silico study confirmed the presence of all the four characteristic motifs of AAA+ superfamily-Walker A, Walker B, Sensor I and Sensor II. Structurally, OsRuvBL1a is similar to RuvB1 from Chaetomium thermophilum. The purified recombinant OsRuvBL1a protein shows unique DNA-independent ATPase activity. Using site-directed mutagenesis, the importance of two conserved motifs (Walker B and Sensor I) in ATPase activity has been also reported with mutants D302N and N332H. The OsRuvBL1a protein unwinds the duplex DNA in the 3' to 5' direction. The presence of unique DNA-independent ATPase and DNA unwinding activities of OsRuvBL1a protein and upregulation of its transcript under abiotic stress conditions suggest its involvement in multiple cellular pathways. The first detailed characterization of plant RuvBL1a in this study may provide important contribution in exploiting the role of RuvB for developing the stress tolerant plants of agricultural importance.

Introgression, Generational Expression and Salinity Tolerance Conferred by the Pea DNA Helicase 45 Transgene into Two Commercial Rice Genotypes, BR28 and BR47

DNA helicase (PDH45) from the pea plant (Pisum sativum) is a member of the DEAD box protein family and plays a vital regulatory role in saline stress tolerance in plants. We previously reported that over-expression of PDH45 gene confers both seedling and reproductive stage salinity tolerance to a Bangladeshi rice landrace, Binnatoa (BA). In this study, transgenic BA-containing PDH45 (♂) was crossed with two different farmer-popular BRRI rice varieties (♀), BR28 and BR47, in a contained net house. F1 plants positive for the transgene and having recipient phenotype were advanced from F1 to F5. Expression of the PDH45 gene was detected in all generations. The expression level of PDH45 was 200-fold higher in the donor compared to the two recipient genotypes but without any effect on their salt stress tolerance ability in various assays. Under 120 mM NaCl stress at seedling stage, all rice genotypes showed vigorous growth, higher chlorophyll content, lower electrolyte leakage and lower LDS (Leaf Damage Score) compared to their corresponding wild types. At the reproductive stage under continuous salinity stress at 80 mM NaCl, the cross-bred lines BR28 and BR47 showed significantly better spikelet fertility and yield per plant, which were two- and 2.5-folds, respectively, than their corresponding wild types. The PDH45 transgene was observed to increase the expression of 6 salt stress-related downstream genes at 150 mM NaCl stress to similar differential degrees in the donor and recipient genotypes. However, the expression of OsLEA was significantly higher in transgenic BR28 compared to transgenic BR47, where the latter shows comparatively higher salt tolerance. The study shows stability of transgene expression across generations. It also demonstrates that there may be an effect of background genotype on transgene expression. Moreover, some downstream effects of the transgene may also be genotype-specific.

Overexpression of Pea DNA Helicase 45 (PDH45) imparts tolerance to multiple abiotic stresses in chili (Capsicum annuum L.)

Imparting tolerance to abiotic stresses is of global importance as they inflict significant yield losses in field as well as in vegetable crops. Transcriptional activators, including helicases are identified to play a pivotal role in stress mitigation. Helicases, also known as molecular motors, are involved in myriad cellular processes that impart intrinsic tolerance to abiotic stresses in plants. Our study demonstrates the potential of a Pea DNA Helicase 45 (PDH45), in combating multiple abiotic stresses in chili. We harnessed Agrobacterium-mediated in planta transformation strategy for the generation of stable, single copy transgenic events. Precise molecular detection of the transgenes by sqRT-PCR coupled with genomic Southern analysis revealed variation in the integration of PDH45 at distinct loci in independent transgenic events. Characterization of five promising transgenic events showed both improved response to an array of simulated abiotic stresses and enhanced expression of several stress-responsive genes. While survival and recovery of transgenic events were significantly higher under gradual moisture stress conditions, under imposition of moderate stress, the transgenic events exhibited invigorated growth and productivity with concomitant improvement in water use efficiency (WUE). Thus, our study, unequivocally demonstrated the cardinal role of PDH45 in alleviating multiple abiotic stresses in chili.

Expression of Pennisetum glaucum Eukaryotic Translational Initiation Factor 4A (PgeIF4A) Confers Improved Drought, Salinity, and Oxidative Stress Tolerance in Groundnut

Eukaryotic translational initiation factor 4A belong to family of helicases, involved in multifunctional activities during stress and non-stress conditions. The eIF4A gene was isolated and cloned from semi-arid cereal crop of Pennisetum glaucum. In present study, the PgeIF4A gene was expressed under the regulation of stress inducible Arabidopsis rd29A promoter in groundnut (cv JL-24) with bar as a selectable marker. The de-embryonated cotyledons were infected with Agrobacterium tumefaciens (LBA4404) carrying rd29A:PgeIF4A construct and generated high frequency of multiple shoots in phosphinothricin medium. Twenty- four T₀ plants showed integration of both nos-bar and rd29A-PgeIF4A gene cassettes in genome with expected amplification products of 429 and 654 bps, respectively. Transgene copy number integration was observed in five T₀ transgenic plants through Southern blot analysis. Predicted Mendelian ratio of segregation (3:1) was noted in transgenic plants at T₁ generation. The T₂ homozygous lines (L1-5, L8-2, and L16-2) expressing PgeIF4A gene were exhibited superior growth performance with respect to phenotypic parameters like shoot length, tap root length, and lateral root formation under simulated drought and salinity stresses compared to the wild type. In addition, the chlorophyll retention was found to be higher in these plants compared to the control plants. The quantitative real time-PCR results confirmed higher expression of PgeIF4A gene in L1-5, L8-3, and L16-2 plants imposed with drought/salt stress. Further, the salt stress tolerance was associated with increase in oxidative stress markers, such as superoxide dismutase accumulation, reactive oxygen species scavenging, and membrane stability in transgenic plants. Taken together our results confirmed that the PgeIF4A gene expressing transgenic groundnut plants exhibited better adaptation to stress conditions.

Aldo-keto reductase-1 (AKR1) protect cellular enzymes from salt stress by detoxifying reactive cytotoxic compounds

Cytotoxic compounds like reactive carbonyl compounds such as methylglyoxal (MG), melandialdehyde (MDA), besides the ROS accumulate significantly at higher levels under salinity stress conditions and affect lipids and proteins that inhibit plant growth and productivity. The detoxification of these cytotoxic compounds by overexpression of NADPH-dependent Aldo-ketoreductase (AKR1) enzyme enhances the salinity stress tolerance in tobacco. The PsAKR1 overexpression plants showed higher survival and chlorophyll content and reduced MDA, H2O2, and MG levels under NaCl stress. The transgenic plants showed reduced levels of Na+ levels in both root and shoot due to reduced reactive carbonyl compounds (RCCs) and showed enhanced membrane stability resulted in higher root growth and biomass. The increased levels of antioxidant glutathione and enhanced activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) suggest AKR1 could protect these enzymes from the RCC induced protein carbonylation by detoxification process. The transgenics also showed higher activity of delta 1-pyrroline-5- carboxylate synthase (P5CS) enzyme resulted in increasedproline levels to maintain osmotic homeostasis. The results demonstrates that the AKR1 protects proteins or enzymes that are involved in scavenging of cytotoxic compounds by detoxifying RCCs generated under salinity stress.

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 200 mM 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.

Integrated Physiological, Proteomic, and Metabolomic Analysis of Ultra Violet (UV) Stress Responses and Adaptation Mechanisms in Pinus radiata

Globally expected changes in environmental conditions, especially the increase of UV irradiation, necessitate extending our knowledge of the mechanisms mediating tree species adaptation to this stress. This is crucial for designing new strategies to maintain future forest productivity. Studies focused on environmentally realistic dosages of UV irradiation in forest species are scarce. Pinus spp. are commercially relevant trees and not much is known about their adaptation to UV. In this work, UV treatment and recovery of Pinus radiata plants with dosages mimicking future scenarios, based on current models of UV radiation, were performed in a time-dependent manner. The combined metabolome and proteome analysis were complemented with measurements of + physiological parameters and gene expression. Sparse PLS analysis revealed complex molecular interaction networks of molecular and physiological data. Early responses prevented phototoxicity by reducing photosystem activity and the electron transfer chain together with the accumulation of photoprotectors and photorespiration. Apart from the reduction in photosynthesis as consequence of the direct UV damage on the photosystems, the primary metabolism was rearranged to deal with the oxidative stress while minimizing ROS production. New protein kinases and proteases related to signaling, coordination, and regulation of UV stress responses were revealed. All these processes demonstrate a complex molecular interaction network extending the current knowledge on UV-stress adaptation in pine.

Simultaneous Expression of PDH45 with EPSPS Gene Improves Salinity and Herbicide Tolerance in Transgenic Tobacco Plants

To cope with the problem of salinity- and weed-induced crop losses, a multi-stress tolerant trait is need of the hour but a combinatorial view of such traits is not yet explored. The overexpression of PDH45 (pea DNA helicase 45) and EPSPS (5-enoylpruvyl shikimate-3-phosphate synthase) genes have been reported to impart salinity and herbicide tolerance. Further, the understanding of mechanism and pathways utilized by PDH45 and EPSPS for salinity and herbicide tolerance will help to improve the crops of economical importance. In the present study, we have performed a comparative analysis of salinity and herbicide tolerance to check the biochemical parameters and antioxidant status of tobacco transgenic plants. Collectively, the results showed that PDH45 overexpressing transgenic lines display efficient tolerance to salinity stress, while PDH45+EPSPS transgenics showed tolerance to both the salinity and herbicide as compared to the control [wild type (WT) and vector control (VC)] plants. The activities of the components of enzymatic antioxidant machinery were observed to be higher in the transgenic plants indicating the presence of an efficient antioxidant defense system which helps to cope with the stress-induced oxidative-damages. Photosynthetic parameters also showed significant increase in PDH45 and PDH45+EPSPS overexpressing transgenic plants in comparison to WT, VC and EPSPS transgenic plants under salinity stress. Furthermore, PDH45 and PDH45+EPSPS synergistically modulate the jasmonic acid and salicylic acid mediated signaling pathways for combating salinity stress. The findings of our study suggest that pyramiding of the PDH45 gene with EPSPS gene renders host plants tolerant to salinity and herbicide by enhancing the antioxidant machinery thus photosynthesis.

New Insight into Quinoa Seed Quality under Salinity: Changes in Proteomic and Amino Acid Profiles, Phenolic Content, and Antioxidant Activity of Protein Extracts

Quinoa (Chenopodium quinoa Willd) is an ancient Andean seed-producing crop well known for its exceptional nutritional properties and resistance to adverse environmental conditions, such as salinity and drought. Seed storage proteins, amino acid composition, and bioactive compounds play a crucial role in determining the nutritional value of quinoa. Seeds harvested from three Chilean landraces of quinoa, one belonging to the salares ecotype (R49) and two to the coastal-lowlands ecotype, VI-1 and Villarrica (VR), exposed to two levels of salinity (100 and 300 mM NaCl) were used to conduct a sequential extraction of storage proteins in order to obtain fractions enriched in albumins/globulins, 11S globulin and in prolamin-like proteins. The composition of the resulting protein fractions was analyzed by one- and two-dimensional polyacrylamide gel electrophoresis. Results confirmed a high polymorphism in seed storage proteins; the two most representative genotype-specific bands of the albumin/globulin fraction were the 30- and 32-kDa bands, while the 11S globulin showed genotype-specific polymorphism for the 40- and 42-kDa bands. Spot analysis by mass spectrometry followed by in silico analyses were conducted to identify the proteins whose expression changed most significantly in response to salinity in VR. Proteins belonging to several functional categories (i.e., stress protein, metabolism, and storage) were affected by salinity. Other nutritional and functional properties, namely amino acid profiles, total polyphenol (TPC) and flavonoid (TFC) contents, and antioxidant activity (AA) of protein extracts were also analyzed. With the exception of Ala and Met in R49, all amino acids derived from protein hydrolysis were diminished in seeds from salt-treated plants, especially in landrace VI-1. By contrast, several free amino acids were unchanged or increased by salinity in R49 as compared with VR and VI-1, suggesting a greater tolerance in the salares landrace. VR had the highest TPC and AA under non-saline conditions. Salinity increased TPC in all three landraces, with the strongest increase occurring in R49, and enhanced radical scavenging capacity in R49 and VR. Overall, results show that salinity deeply altered the seed proteome and amino acid profiles and, in general, increased the concentration of bioactive molecules and AA of protein extracts in a genotype-dependent manner.

mRNA biogenesis-related helicase eIF4AIII from Arabidopsis thaliana is an important factor for abiotic stress adaptation

Similar to other plant species, Arabidopsis has a huge repertoire of predicted helicases, including the eIF4AIII factor, a putative component of the exon junction complex related to mRNA biogenesis. In this article, we integrated evolutionary and functional approaches to have a better understanding of eIF4AIII function in plants. Phylogenetic analysis showed that the mRNA biogenesis-related helicase eIF4AIII is the ortholog of the stress-related helicases PDH45 from Pisum sativum and MH1 from Medicago sativa, suggesting evolutionary and probably functional equivalences between mRNA biogenesis and stress-related plant helicases. Molecular and genetic analyses confirmed the relevance of eIF4AIII during abiotic stress adaptation in Arabidopsis. Therefore, in addition to its function in mRNA biogenesis, eIF4AIII can play a role in abiotic stress adaptation.

Ectopic Expression of an Atypical Hydrophobic Group 5 LEA Protein from Wild Peanut, Arachis diogoi Confers Abiotic Stress Tolerance in Tobacco

Late embryogenesis abundant (LEA) proteins are a group of hydrophilic proteins, which accumulate in plants under varied stress conditions like drought, salinity, extreme temperatures and oxidative stress suggesting their role in the protection of plants against these stresses. A transcript derived fragment (TDF) corresponding to LEA gene, which got differentially expressed in wild peanut, Arachis diogoi against the late leaf spot pathogen, Phaeoisariopsis personata was used in this study. We have cloned its full length cDNA by RACE-PCR, which was designated as AdLEA. AdLEA belongs to the atypical Group 5C of LEA protein family as confirmed by sequence analysis. Group 5C LEA protein subfamily contains Pfam LEA_2 domain and is highly hydrophobic. In native conditions, expression of AdLEA was upregulated considerably upon hormonal and abiotic stress treatments emphasizing its role in abiotic stress tolerance. Subcellular localization studies showed that AdLEA protein is distributed in both nucleus and cytosol. Ectopic expression of AdLEA in tobacco resulted in enhanced tolerance of plants to dehydration, salinity and oxidative stress with the transgenic plants showing higher chlorophyll content and reduced lipid peroxidation as compared to wild type plants. Overexpressed AdLEA tobacco plants maintained better photosynthetic efficiency under drought conditions as demonstrated by chlorophyll fluorescence measurements. These plants showed enhanced transcript accumulation of some stress-responsive genes. Our study also elucidates that ROS levels were significantly reduced in leaves and stomatal guard cells of transgenic plants upon stress treatments. These results suggest that AdLEA confers multiple stress tolerance to plants, which make it a potential gene for genetic modification in plants.

Simultaneous expression of regulatory genes associated with specific drought-adaptive traits improves drought adaptation in peanut

Adaptation of crops to drought-prone rain-fed conditions can be achieved by improving plant traits such as efficient water mining (by superior root characters) and cellular-level tolerance mechanisms. Pyramiding these drought-adaptive traits by simultaneous expression of genes regulating drought-adaptive mechanisms has phenomenal relevance in improving stress tolerance. In this study, we provide evidence that peanut transgenic plants expressing Alfalfa zinc finger 1 (Alfin1), a root growth-associated transcription factor gene, Pennisetum glaucum heat-shock factor (PgHSF4) and Pea DNA helicase (PDH45) involved in protein turnover and protection showed improved tolerance, higher growth and productivity under drought stress conditions. Stable integration of all the transgenes was noticed in transgenic lines. The transgenic lines showed higher root growth, cooler crop canopy air temperature difference (less CCATD) and higher relative water content (RWC) under drought stress. Low proline levels in transgenic lines substantiate the maintenance of higher water status. The survival and recovery of transgenic lines was significantly higher under gradual moisture stress conditions with higher biomass. Transgenic lines also showed significant tolerance to ethrel-induced senescence and methyl viologen-induced oxidative stress. Several stress-responsive genes such as heat-shock proteins (HSPs), RING box protein-1 (RBX1), Aldose reductase, late embryogenesis abundant-5 (LEA5) and proline-rich protein-2 (PRP2), a gene involved in root growth, showed enhanced expression under stress in transgenic lines. Thus, the simultaneous expression of regulatory genes contributing for drought-adaptive traits can improve crop adaptation and productivity under water-limited conditions.

PDH45 transgenic rice maintain cell viability through lower accumulation of Na(+), ROS and calcium homeostasis in roots under salinity stress

Salinity severely affects the growth/productivity of rice, which is utilized as major staple food crop worldwide. PDH45 (pea DNA helicase 45), a member of the DEAD-box helicase family, actively provides salinity stress tolerance, but the mechanism behind this is not well known. Therefore, in order to understand the mechanism of stress tolerance, sodium ion (Na(+)), reactive oxygen species (ROS), cytosolic calcium [Ca(2+)]cyt and cell viability were analyzed in roots of PDH45 transgenic-IR64 rice lines along with wild-type (WT) IR64 rice under salinity stress (100mM and 200 mM NaCl). In addition, the roots of salinity-tolerant (FL478) and susceptible (Pusa-44) rice varieties were also analyzed under salinity stress for comparative analysis. The results reveal that, under salinity stress (100mM and 200 mM NaCl), roots of PDH45 transgenic lines accumulate lower levels of Na(+), ROS and maintain [Ca(2+)]cyt and exhibit higher cell viability as compared with roots of WT (IR64) plants. Similar results were also obtained in the salinity-tolerant FL478 rice. However, the roots of WT and salinity-susceptible Pusa-44 rice accumulated higher levels of Na(+), ROS and [Ca(2+)]cyt imbalance and lower cell viability during salinity stress, which is in contrast to the overexpressing PDH45 transgenic lines and salinity-tolerant FL478 rice. Further, to understand the mechanism of PDH45 at molecular level, comparative expression profiling of 12 cation transporters/genes was also conducted in roots of WT (IR64) and overexpressing PDH45 transgenic lines (L1 and L2) under salt stress (24h of 200 mM NaCl). The expression analysis results show altered and differential gene expression of cation transporters/genes in salt-stressed roots of WT (IR64) and overexpressing transgenic lines (L1 and L2). These observations collectively suggest that, under salinity stress conditions, PDH45 is involved in the regulation of Na(+) level, ROS production, [Ca(2+)]cyt homeostasis, cell viability and cation transporters in roots of PDH45 transgenic-IR64 rice and consequently provide salinity tolerance. Elucidating the detailed regulatory mechanism of PDH45 will provide a better understanding of salinity stress tolerance and further open new ways to manipulate genome to achieve higher agricultural production under stress.

Functional characterization and expression study of sugarcane MYB transcription factor gene PEaMYBAS1 promoter from Erianthus arundinaceus that confers abiotic stress tolerance in tobacco

This work provides a thorough understanding about the function ofcis-acting elements regarding drought, salt, cold and wounding stress.

Spinach (Spinacia oleracea L.) modulates its proteome differentially in response to salinity, cadmium and their combination stress

Cadmium (Cd) contamination and salinity are common stressors in agricultural soils all over the globe. Sensitivity and modulation of plant proteome lead to proper signal execution and adaptation to abiotic stress via molecular responses, which strengthen plant defence system. A comparative proteomic study, employing 2DE-MALDI TOF/TOF MS, of Spinacia oleracea plants exposed to cadmium (50 μg CdCl2 g(-1) soil), salinity (10 mg NaCl g(-1) soil) and their combination (NaCl + Cd) was conducted to understand the minimum common adaptation to multiple stress. Analysis of 2D gel maps showed significant increase and decrease in relative abundance of 14 and 39 proteins by Cd; 11 and 46 by salinity and 22 and 37 by combined stress of Cd and salinity, respectively. Peptide mass fingerprinting (PMF) helped in the identification of maturase K and PPD4 with increased relative abundance under all stresses; whereas salinity stress and combination stress silenced the presence of one protein (polycomb protein EZ2) and two proteins (cellulose synthase-like protein and ubiquitin conjugation factor E4), respectively. The identified proteins were functionally associated with signal transduction (15%), protein synthesis (16%), stress response and defence (33%), photosynthesis (13%), plant growth/cell division (9%), energy generation (4%), transport (4%), secondary metabolism (3%), and cell death (3%); clearly indicating the importance and necessity of keeping a higher ratio of defence and disease-responsive proteins. The results suggest that plant may increase the abundance of defence proteins and may also lower the abundance of catabolic proteins. Proteins with altered ratios of abundance belonged to different functional categories, suggesting that plants have differential mechanisms to respond to Cd, salinity, and their combined stress, but with unique sets of proteins.

Stress-induced Oryza sativa BAT1 dual helicase exhibits unique bipolar translocation

HLA-B associated transcript 1 (BAT1) protein, also named as spliceosome RNA helicase UAP56, is a member of the DExD/H-box family of helicases. However, regulation under stress, biochemical properties, and functions of plant homologue of BAT1 are poorly understood. Here, we report the purification and detailed biochemical characterization of the Oryza sativa homologue of BAT1 (OsBAT1/UAP56) protein (52 kDa) and regulation of its transcript under abiotic stress. OsBAT1 transcript levels are enhanced in rice seedlings in response to abiotic stress including salt stress and abscisic acid. Purified OsBAT1 protein exhibits the DNA- and RNA-dependent ATPase, RNA helicase, and DNA- and RNA-binding activities. Interestingly OsBAT1 also exhibits unique DNA helicase activity, which has not been reported so far in any BAT1 homologue. Moreover, OsBAT1 translocates in both the 3' to 5' and 5' to 3' directions, which is also a unique property. The K m value for OsBAT1 DNA helicase is 0.9753 nM and for RNA helicase is 1.7536 nM, respectively. This study demonstrates several unique characteristics of OsBAT1 especially its ability to unwind both DNA and RNA duplexes; bipolar translocation and its transcript upregulation under abiotic stresses indicate that it is a multifunctional protein. Overall, this study represents significant contribution in advancing our knowledge regarding functions of OsBAT1 in RNA and DNA metabolism and its putative role in abiotic stress signaling in plants.

Salt resistance genes revealed by functional metagenomics from brines and moderate-salinity rhizosphere within a hypersaline environment

Hypersaline environments are considered one of the most extreme habitats on earth and microorganisms have developed diverse molecular mechanisms of adaptation to withstand these conditions. The present study was aimed at identifying novel genes from the microbial communities of a moderate-salinity rhizosphere and brine from the Es Trenc saltern (Mallorca, Spain), which could confer increased salt resistance to Escherichia coli. The microbial diversity assessed by pyrosequencing of 16S rRNA gene libraries revealed the presence of communities that are typical in such environments and the remarkable presence of three bacterial groups never revealed as major components of salt brines. Metagenomic libraries from brine and rhizosphere samples, were transferred to the osmosensitive strain E. coli MKH13, and screened for salt resistance. Eleven genes that conferred salt resistance were identified, some encoding for well-known proteins previously related to osmoadaptation such as a glycerol transporter and a proton pump, whereas others encoded proteins not previously related to this function in microorganisms such as DNA/RNA helicases, an endonuclease III (Nth) and hypothetical proteins of unknown function. Furthermore, four of the retrieved genes were cloned and expressed in Bacillus subtilis and they also conferred salt resistance to this bacterium, broadening the spectrum of bacterial species in which these genes can function. This is the first report of salt resistance genes recovered from metagenomes of a hypersaline environment.

Proteomic Analysis Provides New Insights in Phosphorus Homeostasis Subjected to Pi (Inorganic Phosphate) Starvation in Tomato Plants (Solanum lycopersicum L.)

Phosphorus is a major nutrient acquired by plants via high-affinity inorganic phosphate (Pi) transporters. To determine the adaptation and homeostasis strategy to Pi starvation, we compared the proteome analysis of tomato leaves that were treated with and without Pi (as KH2PO4) for 10 days. Among 600 reproducible proteins on 2-DE gels 46 of them were differentially expressed. These proteins were involved in major metabolic pathways, including photosynthesis, transcriptional/translational regulations, carbohydrate/energy metabolism, protein synthesis, defense response, and other secondary metabolism. The results also showed that the reduction in photosynthetic pigments lowered P content under -Pi treatments. Furthermore, high-affinity Pi transporters (lePT1 and lePT2) expressed in higher amounts under -Pi treatments. Also, the accumulation of Pi transporters was observed highly in the epidermis and palisade parenchyma under +Pi treatments compared to -Pi treatments. Our data suggested that tomato plants developed reactive oxygen species (ROS) scavenging mechanisms to cope with low Pi content, including the up-regulation of proteins mostly involved in important metabolic pathways. Moreover, Pi-starved tomato plants increased their internal Pi utilization efficiency by increasing the Pi transporter genes and their rational localization. These results thus provide imperative information about how tomato plants respond to Pi starvation and its homeostasis.

Introduction of Pea DNA Helicase 45 Into Sugarcane (Saccharum spp. Hybrid) Enhances Cell Membrane Thermostability And Upregulation Of Stress-responsive Genes Leads To Abiotic Stress Tolerance

DNA helicases are motor proteins that play an essential role in nucleic acid metabolism, by providing a duplex-unwinding function. To improve the drought and salinity tolerance of sugarcane, a DEAD-box helicase gene isolated from pea with a constitutive promoter, Port Ubi 2.3 was transformed into the commercial sugarcane variety Co 86032 through Agrobacterium-mediated transformation, and the transgenics were screened for tolerance to soil moisture stress and salinity. The transgene integration was confirmed through polymerase chain reaction, and the V 0 transgenic events showed significantly higher cell membrane thermostability under normal irrigated conditions. The V 1 transgenic events were screened for tolerance to soil moisture stress and exhibited significantly higher cell membrane thermostability, transgene expression, relative water content, gas exchange parameters, chlorophyll content, and photosynthetic efficiency under soil moisture stress compared to wild-type (WT). The overexpression of PDH45 transgenic sugarcane also led to the upregulation of DREB2-induced downstream stress-related genes. The transgenic events demonstrated higher germination ability and better chlorophyll retention than WT under salinity stress. Our results suggest the possibility for development of increased abiotic stress tolerant sugarcane cultivars through overexpression of PDH45 gene. Perhaps this is the first report, which provides evidence for increased drought and salinity tolerance in sugarcane through overexpression of PDH45.

Pea lectin receptor-like kinase functions in salinity adaptation without yield penalty, by alleviating osmotic and ionic stresses and upregulating stress-responsive genes

Lectin receptor-like kinases (LecRLKs) are members of RLK family composed of lectin-like extracellular recognition domain, transmembrane domain and cytoplasmic kinase domain. LecRLKs are plasma membrane proteins believed to be involved in signal transduction. However, most of the members of the protein family even in plants have not been functionally well characterized. Herein, we show that Pisum sativum LecRLK (PsLecRLK) localized in plasma membrane systems and/or other regions of the cell and its transcript upregulated under salinity stress. Overexpression of PsLecRLK in transgenic tobacco plants confers salinity stress tolerance by alleviating both the ionic as well the osmotic component of salinity stress. The transgenic plants show better tissue compartmentalization of Na(+) and higher ROS scavenging activity which probably results in lower membrane damage, improved growth and yield maintenance even under salinity stress. Also, expression of several genes involved in cellular homeostasis is perturbed by PsLecRLK overexpression. Alleviation of osmotic and ionic components of salinity stress along with reduced oxidative damage and upregulation of stress-responsive genes in transgenic plants under salinity stress conditions could be possible mechanism facilitating enhanced stress tolerance. This study presents PsLecRLK as a promising candidate for crop improvement and also opens up new avenue to investigate its signalling pathway.

Virus-induced gene silencing reveals control of reactive oxygen species accumulation and salt tolerance in tomato by γ-aminobutyric acid metabolic pathway

γ-Aminobutyric acid (GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway (GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases (SlGADs), GABA transaminases (SlGABA-Ts) and succinic semialdehyde dehydrogenase (SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs (GABA biosynthetic genes) and SlGABA-Ts (GABA catabolic genes) led to increased accumulation of reactive oxygen species (ROS) as well as salt sensitivity under 200 mm NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA-Ts-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to γ-hydroxybutyrate as reported previously in Arabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and γ-hydroxybutyrate and subsequent ROS accumulation under salt stress.

Overexpression of EaDREB2 and pyramiding of EaDREB2 with the pea DNA helicase gene (PDH45) enhance drought and salinity tolerance in sugarcane (Saccharum spp. hybrid)

KEY MESSAGE

EaDREB2 overexpressed in sugarcane enhanced tolerance to drought and salinity. When co-transformed with plant DNA helicase gene, DREB2 showed greater level of salinity tolerance than in single-gene transgenics. Drought is one of the most challenging agricultural issues limiting sustainable sugarcane production and can potentially cause up to 50 % yield loss. DREB proteins play a vital regulatory role in abiotic stress tolerance in plants. We previously reported that expression of EaDREB2 is enhanced by drought stress in Erianthus arundinaceus. In this study, we have isolated the DREB2 gene from E. arundinaceus, transformed one of the most popular sugarcane variety Co 86032 in tropical India with EaDREB2 through Agrobacterium-mediated transformation, pyramided the EaDREB2 gene with the gene coding for PDH45 driven by Port Ubi 2.3 promoter through particle bombardment and evaluated the V1 transgenics for soil deficit moisture and salinity stresses. Soil moisture stress was imposed at the tillering phase by withholding irrigation. Physiological, molecular and morphological parameters were used to assess drought tolerance. Salinity tolerance was assessed through leaf disc senescence and bud sprout assays under salinity stress. Our results indicate that overexpression of EaDREB2 in sugarcane enhances drought and salinity tolerance to a greater extent than the untransformed control plants. This is the first report of the co-transformation of EaDREB2 and PDH45 which shows higher salinity tolerance but lower drought tolerance than EaDREB2 alone. The present study seems to suggest that, for combining drought and salinity tolerance together, co-transformation is a better approach.

Alterations in root proteome of salt-sensitive and tolerant barley lines under salt stress conditions

Salinity is one of the most important abiotic stresses causing a significant reduction of crop plants yield. To gain a better understanding of salinity tolerance mechanisms in barley (Hordeum vulgare), we investigated the changes in root proteome of salt-sensitive (DH14) and tolerant (DH187) lines in response to salt-stress. The seeds of both barley lines were germinating in water or in 100mM NaCl for 6 days. The root proteins were separated by two-dimensional gel electrophoresis. To identify proteins regulated in response to salt stress, MALDI-TOF/TOF mass spectrometry was applied. It was demonstrated that the sensitive and tolerant barley lines respond differently to salt stress. Some of the identified proteins are well-documented as markers of salinity resistance, but several proteins have not been detected in response to salt stress earlier, although they are known to be associated with other abiotic stresses. The most significant differences concerned the proteins that are involved in signal transduction (annexin, translationally-controlled tumor protein homolog, lipoxygenases), detoxification (osmotin, vacuolar ATP-ase), protein folding processes (protein disulfide isomerase) and cell wall metabolism (UDP-glucuronic acid decarboxylase, β-d-glucan exohydrolase, UDP-glucose pyrophosphorylase). The results suggest that the enhanced salinity tolerance of DH187 line results mainly from an increased activity of signal transduction mechanisms eventually leading to the accumulation of stress protective proteins and cell wall structure changes.

Progress in genetic engineering of peanut (Arachis hypogaea L.)--a review

Peanut (Arachis hypogaea L.) is a major species of the family, Leguminosae, and economically important not only for vegetable oil but as a source of proteins, minerals and vitamins. It is widely grown in the semi-arid tropics and plays a role in the world agricultural economy. Peanut production and productivity is constrained by several biotic (insect pests and diseases) and abiotic (drought, salinity, water logging and temperature aberrations) stresses, as a result of which crop experiences serious economic losses. Genetic engineering techniques such as Agrobacterium tumefaciens and DNA-bombardment-mediated transformation are used as powerful tools to complement conventional breeding and expedite peanut improvement by the introduction of agronomically useful traits in high-yield background. Resistance to several fungal, virus and insect pest have been achieved through variety of approaches ranging from gene coding for cell wall component, pathogenesis-related proteins, oxalate oxidase, bacterial chloroperoxidase, coat proteins, RNA interference, crystal proteins etc. To develop transgenic plants withstanding major abiotic stresses, genes coding transcription factors for drought and salinity, cytokinin biosynthesis, nucleic acid processing, ion antiporter and human antiapoptotic have been used. Moreover, peanut has also been used in vaccine production for the control of several animal diseases. In addition to above, this study also presents a comprehensive account on the influence of some important factors on peanut genetic engineering. Future research thrusts not only suggest the use of different approaches for higher expression of transgene(s) but also provide a way forward for the improvement of crops.

PDH45 overexpressing transgenic tobacco and rice plants provide salinity stress tolerance via less sodium accumulation

Salinity stress negatively affects the crop productivity worldwide, including that of rice. Coping with these losses is a major concern for all countries. The pea DNA helicase, PDH45 is a unique member of helicase family involved in the salinity stress tolerance. However, the exact mechanism of the PDH45 in salinity stress tolerance is yet to be established. Therefore, the present study was conducted to investigate the mechanism of PDH45-mediated salinity stress tolerance in transgenic tobacco and rice lines along with wild type (WT) plants using CoroNa Green dye based sodium localization in root and shoot sections. The results showed that under salinity stress root and shoot of PDH45 overexpressing transgenic tobacco and rice accumulated less sodium (Na(+)) as compared to their respective WT. The present study also reports salinity tolerant (FL478) and salinity susceptible (Pusa-44) varieties of rice accumulated lowest and highest Na(+) level, respectively. All the varieties and transgenic lines of rice accumulate differential Na(+) ions in root and shoot. However, roots accumulate high Na(+) as compared to the shoots in both tobacco and rice transgenic lines suggesting that the Na(+) transport in shoot is somehow inhibited. It is proposed that the PDH45 is probably involved in the deposition of apoplastic hydrophobic barriers and consequently inhibit Na(+) transport to shoot and therefore confers salinity stress tolerance to PDH45 overexpressing transgenic lines. This study concludes that tobacco (dicot) and rice (monocot) transgenic plants probably share common salinity tolerance mechanism mediated by PDH45 gene.