Deciphering the potential of Sargassum tenerrimum extract: metabolic profiling and pathway analysis of groundnut (Arachis hypogaea) in response to Sargassum extract and Sclerotium rolfsii.

Seaweed extracts have enormous potential as bio-stimulants and demonstrated increased growth and yield in different crops. The presence of physiologically active component stimulate plant stress signaling pathways, enhances growth and productivity, as well as serve as plant defense agents. The seaweed extracts can reduce the use of chemicals that harm the environment for disease management. In the present study, the Sargassum tenerrimum extract treatment was applied, alone and in combination with Sclerotium rolfsii, to Arachis hypogea, to study the differential metabolite expression. The majority of metabolites showed maximum accumulation with Sargassum extract-treated plants compared to fungus-treated plants. The different classes of metabolite compounds like sugars, carboxylic acids, polyols, showed integrated peaks in different treatments of plants. The sugars were higher in Sargassum extract and Sargassum extract + fungus treatments compared to control and fungus treatment, respectively. Interestingly, Sargassum extract + fungus treatment showed maximum accumulation of carboxylic acids. Pathway enrichment analysis showed regulation of different metabolites, highest impact with galactose metabolism pathway, identifying sucrose, myo-inositol, glycerol and fructose. The differential metabolite profiling and pathway analysis of groundnut in response to Sargassum extract and S. rolfsii help in understanding the groundnut- S. rolfsii interactions and the potential role of the Sargassum extract towards these interactions. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01418-9.

AlRab7 from Aeluropus lagopoides ameliorates ion toxicity in transgenic tobacco by regulating hormone signaling and reactive oxygen species homeostasis.

The plants endomembrane system of the cellular compartments with its complex membrane trafficking network facilitates transport of macromolecules. The endomembrane dynamics are essential for maintaining basic and specific cellular functions including adaptation to the extracellular environment. The plant vacuole serves as a reservoir for nutrients and toxic metabolites and performs detoxification processes to maintain cellular homeostasis. The overexpression of AlRab7, a vesicle trafficking gene from Aeluropus lagopoides, improved germination and growth and reduced ionic and oxidative stress in transgenics. Moreover, the root and shoot of transgenic tobacco showed differential accumulation of phytohormone ABA and IAA with different ionic stresses. The improved growth (root and shoot length) can be co-related with higher IAA accumulation with NaCl stress. The low Na+ /K+ ratio with different NaCl stress treatments indicates better ion homeostasis in transgenics. Furthermore, the increased stomatal density and higher number of open stomata on both leaf surfaces in transgenics during NaCl stress suggest better gaseous exchange/functioning of guard cells. The maintained or increased superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase antioxidative enzyme activities suggest that an extensive reactive oxygen species (ROS) scavenging system was triggered to detoxify cellular ROS, which remained at low levels in transgenics during the different stress treatments. Our results suggest that the AlRab7 transgenic tobacco ameliorates ionic stress by facilitating differential and selective ion transport at vacuolar membrane regulating hormone signaling, ROS homeostasis, stomatal development, and movement.

Dehydration responsive element binding transcription factors and their applications for the engineering of stress tolerance.

Dehydration responsive element binding (DREB) factors or CRT element binding factors (CBFs) are members of the AP2/ERF family, which comprises a large number of stress-responsive regulatory genes. This review traverses almost two decades of research, from the discovery of DREB/CBF factors to their optimization for application in plant biotechnology. In this review, we describe (i) the discovery, classification, structure, and evolution of DREB genes and proteins; (ii) induction of DREB genes by abiotic stresses and involvement of their products in stress responses; (iii) protein structure and DNA binding selectivity of different groups of DREB proteins; (iv) post-transcriptional and post-translational mechanisms of DREB transcription factor (TF) regulation; and (v) physical and/or functional interaction of DREB TFs with other proteins during plant stress responses. We also discuss existing issues in applications of DREB TFs for engineering of enhanced stress tolerance and improved performance under stress of transgenic crop plants.

Overexpression of a novel SbMYB15 from Salicornia brachiata confers salinity and dehydration tolerance by reduced oxidative damage and improved photosynthesis in transgenic tobacco.

MAIN CONCLUSION: SbMYB15, R2R3-type MYB was induced by the different stresses, and conferred stress tolerance in transgenic tobacco by regulating the expression of stress-responsive genes. MYBs are the master regulators of various metabolic processes and stress responses in plants. In this study, we functionally characterised a R2R3-type SbMYB15 transcription factor (TF) from the extreme halophyte Salicornia brachiata. The SbMYB15 acts as a transcriptional activator. Transcriptional analysis showed that SbMYB15 transcript was strongly upregulated in red shoots and was also induced by different stresses; however, its expression remained unchanged with ABA. Overexpression of SbMYB15 in tobacco significantly improved salinity and dehydration tolerance. The enhanced tolerance of the transgenic plants was defined by the changes in chlorophyll, malondialdehyde (MDA), proline, total soluble sugar and total amino acid contents. The transgenic plants exhibited a higher membrane stability and reduced electrolyte leakage, H2O2 and O 2 (-) content compared to the wild type (WT). With ionic stress, transgenics showed a low Na(+) and a high K(+) content. In the transgenic plants, the expression of stress-responsive genes such as LEA5, ERD10D, PLC3, LTP1, HSF2, ADC, P5CS, SOD and CAT was enhanced in the presence of salinity, dehydration and heat. Exposure to gradual salinity and dehydration resulted in an increased stomatal conductance, water use efficiency, photosynthesis rate, photochemical quenching and reduced transpiration rate. Thus, SbMYB15 served as an important mediator of stress responses regulating different stress signalling pathways, leading to enhanced stress tolerance.

Pathogenesis related-10 proteins are small, structurally similar but with diverse role in stress signaling.

Pathogenesis related-10 proteins are small proteins with cytosolic localization, conserved three dimensional structures and single intron at 185 bp position. These proteins have a broad spectrum of roles significantly in biotic and abiotic stresses. The RNase activity, ligand binding activity, posttranslational modification (phosphorylation) and phytohormone signaling provide some information into the mechanism of the regulation of PR-10 proteins, however the presence of isoforms makes it difficult to decipher its exact mode of function. The involvement of phosphorylation/dephosphorylation events in its activation is interesting and provides unique and unbiased insights into the complexity of its regulation. Studies on upstream region of different PR-10 genes indicate the presence of cis-acting elements for WRKY, RAVI, bZ1P, ERF, SEBF and Pti4 transcription factors indicating their role in regulating PR-10 promoter. In this review, we discuss in detail the structure and mechanism of regulation of PR-10 proteins.

Rab7 GTPase-Mediated stress signaling enhances salinity tolerance in AlRabring7 tobacco transgenics by modulating physio-biochemical parameters.

The RING-type E3 ligases play a significant role in stress signaling, primarily through post-translational regulation. Ubiquitination is a crucial post-translational modification that regulates the turnover and activity of proteins. The overexpression of AlRabring7, RING-HC E3 Ub ligase in tobacco provides insights into the regulation of salinity and ABA signaling in transgenic tobacco. The seed germination potential of AlRabring7 transgenics was higher than WT, with NaCl and ABA treatments. The transgenics showed improved morpho-physio-biochemical parameters in response to salinity and ABA treatments. The photosynthetic pigments, soluble sugars, reducing sugars and proline increased in transgenics in response to NaCl and ABA treatments. The decreased ROS accumulation in transgenics on NaCl and ABA treatments can be co-related to improved activity of enzymatic and non-enzymatic antioxidants. The potential of transgenics to maintain ABA levels with ABA treatment, highlights the active participation of ABA feedback loop mechanism. Interestingly, the ability of AlRabring7 transgenics to upregulate Rab7 protein, suggests its role in facilitating vacuolar transport. Furthermore, the improved potassium accumulation and reduced sodium content indicate an efficient ion regulation mechanism in transgenic plants facilitating higher stomatal opening. The expression of downstream ion transporter (NbNHX1 and NbVHA1), ABA signaling (NbABI2 and NbABI5) and vesicle trafficking (NbMON1) responsive genes were upregulated with stress. The present study, reports that AlRabring7 participates in maintaining vacuolar transport, ion balance, ROS homeostasis, stomatal regulation through activation of Rab7 protein and regulation of downstream stress-responsive during stress. This emphasizes the potential of AlRabring7 gene for improved performance and resilience in challenging environments.

Transcriptomic analysis towards identification of defence-responsive genes and pathways upon application of Sargassum seaweed extract on tomato plants infected with Macrophominaphaseolina.

The charcoal-rot caused by Macrophomina phaseolina is one of the major disease in many economically important crop plants including tomato. The molecular responses of the host plant against the M. phaseolina are poorly stated. In the present study, for the first time the molecular insight of tomato-Macrophomina interaction and Sargassum tenerrimum extract (SE) toward managing disease through RNA-seq approach is established. A total of 449 million high-quality reads (HQRs) were obtained and aligned to the tomato genome with an average mapping of 89.12%. The differentially expressed genes (DEGs) regulated across the different treatment pairs were identified. Several DEGs, such as receptor-like kinases (SlRLKs), transcription factors including SlWRKY70, SlGRAS4, SlERF4, SlERF25, pathogenesis related-1 (SlPR1), SlPR2, endochitinase and peroxidase were significantly up-regulated in SE + Macrophomina treated sample as compared to only Macrophomina treated sample. The crosstalk between salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) was a key factor to regulate resistance in tomato during SE + Macrophomina treatment. The KEGG pathway including plant hormone signal transduction, plant-pathogen interaction and mitogen-activated protein kinase (MAPK) signaling pathway were significantly enriched. The RNA-seq data were validated through qPCR using 12 disease-responsive genes and correlated significantly with R2 = 0.73. The present study suggests that SE act as an elicitor molecule and activate the defence-related pathways similar to PAMP-triggered immunity in tomato. The jasmonic acid (JA) mediated signaling pathway was identified as a key factor to induce resistance in tomato against Macrophomina infection. The present study depicts the beneficial effects of SE by regulating molecular mechanism towards defence responses in tomato against Macrophomina infection. The application of SE brings out new prospects to induce disease tolerance in the agricultural crops. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03565-4.

The Jatropha leaf curl Gujarat virus on infection in Jatropha regulates the sugar and tricarboxylic acid cycle metabolic pathways.

Jatropha, a popular biodiesel crop, suffers severe losses due to Jatropha leaf curl Gujarat virus (JLCuGV) infection in Gujarat (India). Metabolite profiling can help to understand the plant's innate immune response to geminivirus infection. Our study aims to compare metabolic profiles of an infected and healthy plant to unravel the changes in biochemical pathways on geminivirus infection in Jatropha. Gas chromatography-mass spectrometry (GC-MS) analysis was performed in healthy and infected tissue of Jatropha field plants which were identified to be infected with geminivirus. GC-MS analysis revealed that the metabolites like sugars, polyols, carboxylic acids, fatty acids, polyphenols, and amino acids were regulated on JLCuGV infection. The sugars (glucose, sucrose, and fructose) increased, while carboxylic acids (malic acid, citric acid and quinic acid) and polyols (galactinol, butanetriol, triethylene glycol, myo-inositol, erythritol) decreased remarkably in infected Jatropha tissue. All these metabolic variations indicated that sugar metabolism and tricarboxylic acid (TCA) cycle pathways are regulated as a defense response and a disease development response to geminivirus infection in Jatropha.

Mechanism of high affinity potassium transporter (HKT) towards improved crop productivity in saline agricultural lands.

Glycophytic plants are susceptible to salinity and their growth is hampered in more than 40 mM of salt. Salinity not only affects crop yield but also limits available land for farming by decreasing its fertility. Presence of distinct traits in response to environmental conditions might result in evolutionary adaptations. A better understanding of salinity tolerance through a comprehensive study of how Na+ is transported will help in the development of plants with improved salinity tolerance and might lead to increased yield of crops growing in strenuous environment. Ion transporters play pivotal role in salt homeostasis and maintain low cytotoxic effect in the cell. High-affinity potassium transporters are the critical class of integral membrane proteins found in plants. It mainly functions to remove excess Na+ from the transpiration stream to prevent sodium toxicity in the salt-sensitive shoot and leaf tissues. However, there are large number of HKT proteins expressed in plants, and it is possible that these members perform in a wide range of functions. Understanding their mechanism and functions will aid in further manipulation and genetic transformation of different crops. This review focuses on current knowledge of ion selectivity and molecular mechanisms controlling HKT gene expression. The current review highlights the mechanism of different HKT transporters from different plant sources and how this knowledge could prove as a valuable tool to improve crop productivity.

Expression of B. subtilis Phytase gene driven by fruit specific E8 promoter for enhanced minerals, metabolites and phytonutrient in cucumber fruit.

The fruit nutrigenomics is an interesting and important research area towards nutrition enhancement. The phytic acid is one of the major antinutrient compound, present in seeded fruits and crops. It hinders the absorption of iron (Fe), zinc (Zn), magnesium (Mg), potassium (K) and calcium (Ca), causing mineral deficiencies. In the present study, the BsPhy gene was overexpressed in the cucumber fruits using the tomato fruit specific E8 and constitutive CaMV 35S promoter. The E8 promoter imparted heterologous expression of GUS gene in cucumber fruits, furthermore, the fruit specific expression of E8 promoter with BsPhy gene was confirmed in transgenics (E8::BsPhy) using anti rabbit-phytase antibody. The physio-biochemical analysis of transgenics revealed, maximum phytase activity in E8::BsPhy cucumber fruits at 10 days after anthesis (DAA) compared to 35S::BsPhy and wild-type (WT) fruits. Consequently, E8::BsPhy fruits also showed increased amount of inorganic phosphorus (Pi), total phosphorus (P), minerals (Zn, Fe, Mg, K, Ca), total carotenoid and other macronutrients at 10 DAA compared to 35S::BsPhy fruits. The metabolite profiling of fruits (10 DAA) showed increased sugars, amino acids, sugar acids and polyols, in both E8::BsPhy and 35S::BsPhy transgenics suggesting higher phytate metabolism, compared to WT fruits. Interestingly, both the transgenic fruits showed higher fruit biomass and yield along with improved nutritional quality, which can be attributed to increased P and Zn contents in transgenic fruits, compared to WT fruits. Our findings reveal that the BsPhy gene enhances minerals and macronutrients in transgenic cucumber fruits making it nutritious and healthy.

WRKY: its structure, evolutionary relationship, DNA-binding selectivity, role in stress tolerance and development of plants.

The plants during their sessile, autotrophic lifestyle are affected by wide range of environmental signals and regulate complex patterns of gene expression with the help of transcription factors. The WRKY transcription factors are considered as plant-specific, however, are also reported in protist, slime mold, fern and pine. The WRKY name is coined from its highly conserved 60 amino acid long WRKY domain. These TFs show W box specific binding which is also influenced by the W box flanking sequence. During evolution, the family has expanded in different patterns to facilitate distinct cellular, developmental, and physiological role in plants. The WRKY TFs form one of the largest families in flowering plants, and play a broad spectrum regulatory role as positive and negative regulators of plant defense regulation, abiotic stresses and also involved in growth and development of plants.

Molecular cloning and characterization of high-affinity potassium transporter (AlHKT2;1) gene promoter from halophyte Aeluropus lagopoides.

HKT subfamily II functions as Na+- K+ co-transporter and prevents plants from salinity stress. A 760 bp promoter region of AlHKT2;1 was isolated, sequenced and cloned. The full length promoter D1, has many cis-regulatory elements like MYB, MBS, W box, ABRE etc. involved in abiotic stress responses. D1 and subsequent 5' deletions were cloned into pCAMBIA1301 and studied for its efficacy in stress conditions in heterologous system. Blue colour staining was observed in flower petals, anther lobe, and dehiscence slit of anther in T0 plants. The T1 seedlings showed staining in leaf veins, shoot vasculature and root except root tip. T1 seedlings were subjected to NaCl, KCl, NaCl + KCl and ABA stresses. GUS activity was quantified by 4-methylumbelliferyl glucuronide (4-MUG) assay under control and stress conditions. The smallest deletion- D4 also showed GUS expression but highest activity was observed in D2 as compared to full length promoter and other deletions. The electrophoretic mobility shift assay using stress-induced protein with different promoter deletions revealed more prominent binding in D2. These results suggest that AlHKT2;1 promoter is involved in abiotic stress response and deletion D2 might be sufficient to drive the stress-inducible expression of various genes involved in providing stress tolerance in plants.

Artificial miRNA mediated resistance in tobacco against Jatropha leaf curl Gujarat virus by targeting RNA silencing suppressors.

The leaf curl disease of Jatropha caused by geminiviruses results in heavy economic losses. In the present study, we report the identification of a new strain of a Jatropha leaf curl Gujarat virus (JLCuGV), which encodes six ORFs with each one having RNA silencing suppressor activity. Therefore, three artificial microRNAs (amiRNAs; C1/C4, C2/C3 and V1/V2) were designed employing overlapping regions, each targeting two ORFs of JLCuGV genomic DNA and transformed in tobacco. The C1/C4 and C2/C3 amiRNA transgenics were resistant while V1/V2 amiRNA transgenics were tolerant against JLCuGV. The relative level of amiRNA inversely related to viral load indicating a correlation with disease resistance. The assessment of photosynthetic parameters suggests that the transgenics perform significantly better in response to JLCuGV infiltration as compared to wild type (WT). The metabolite contents were not altered remarkably in amiRNA transgenics, but sugar metabolism and tricarboxylic acid (TCA) cycle showed noticeable changes in WT on virus infiltration. The overall higher methylation and demethylation observed in amiRNA transgenics correlated with decreased JLCuGV accumulation. This study demonstrates that amiRNA transgenics showed enhanced resistance to JLCuGV while efficiently maintaining normalcy in their photosynthesis and metabolic pathways as well as homeostasis in the methylation patterns.

Overexpression of PgDREB2A transcription factor enhances abiotic stress tolerance and activates downstream stress-responsive genes.

The DREB transcription factors comprise conserved ERF/AP2 DNA-binding domain, bind specifically to DRE/CRT motif and regulate abiotic stress mediated gene expression. In this study we show that PgDREB2A from Pennisetum glaucum is a powerful transcription factor to engineer multiple stress tolerance in tobacco plants. The PgDREB2A protein lacks any potential PEST sequence, which is known to act as a signal peptide for protein degradation. Therefore, the transgenic tobacco plants were raised using full-length cDNA without modification. The transgenics exhibited enhanced tolerance to both hyperionic and hyperosmotic stresses. At lower concentration of NaCl and mannitol, seed germination and seedling growth was similar in WT and transgenic, however at higher concentration germination in WT decreased significantly. D15 and D46 lines showed 4-fold higher germination percent at 200 mM NaCl. At 400 mM mannitol seed germination in WT was completely arrested, whereas in transgenic line it was more than 50%. Seedlings of D15 and D46 lines showed better growth like leaf area, root number, root length and fresh weight compared to wild type for both the stresses. The quantitative Real time PCR of transgenic showed higher expression of downstream genes NtERD10B, HSP70-3, Hsp18p, PLC3, AP2 domain TF, THT1, LTP1 and heat shock (NtHSF2) and pathogen-regulated (NtERF5) factors with different stress treatments.

Overexpression of JcWRKY2 confers increased resistance towards Macrophomina phaseolina in transgenic tobacco.

WRKY proteins are plant-specific transcription factors (TFs), and form one of the largest families and are involved in plant development and responses to stress. The salicylic acid (SA) responsive WRKY family auto or cross-regulate the defence stress signalling pathways. In this study, we functionally validated the role of JcWRKY2 gene from biofuel crop Jatropha curcas towards improving resistance to tobacco transgenic against charcoal rot causing necrotrophic fungus, Macrophomina phaseolina. The microscopic studies revealed that JcWRKY2 participated in preventing the spread of infection in transgenic. The generation of H2O2 during M. phaseolina and combinatorial stress in transgenic induces the expression and activity of antioxidant enzymes. The transcript expression of SA biosynthetic (NtICS1) gene, pathogenesis-related (NtPR-10) gene and antioxidative enzymes (NtCAT1 and NtSOD) gene revealed that JcWRKY2 transgenic play a role in SA-mediated, antioxidative enzymes regulation during biotic challenges. The study highlights the potential of JcWRKY2 as an important regulator for plant biotic stress responses through the SA-dependent pathway.

The AlRabring7 E3-Ub-ligase mediates AlRab7 ubiquitination and improves ionic and oxidative stress tolerance in Saccharomyces cerevisiae.

The maintenance of ROS homeostasis, membrane biogenesis and recycling of molecules are common stress responses involving specific and complex regulatory network. Ubiquitination is an important and common mechanism which facilitates environmental adaptation in eukaryotes. In the present study we have cloned the AlRabring7, an E3-Ub-ligase, previously identified as AlRab7 interacting partner. The role of AlRabring7 for ubiquitinating AlRab7 and facilitating stress tolerance is analysed. The AlRabring7, with an open-reading frame of 702 bp encodes a protein of 233 amino acids, with RING-HC domain of 40 amino acids. In silico analysis shows that AlRabring7 is a C3HC4-type RING E3 Ub ligase. The protein - protein docking show interaction dynamics between AlRab7-AlRabring7-Ubiquitin proteins. The AlRab7 and AlRabring7 transcript showed up-regulation in response to different salts i.e: NaCl, KCl, CaCl2, NaCl + KCl, NaCl + CaCl2, imposing ionic as well as hyperosmotic stress, and also with oxidative stress by H2O2 treatment. Interestingly, the AlRabring7 showed early transcript expression with maximum expression in shoots on combinatorial stresses. The AlRab7 showed delayed and maximum expression with NaCl + CaCl2 stress treatment. The AlRab7 complements yeast ypt7Δ mutants and restored the fragmented vacuole. The in vitro ubiquitination assay revealed that AlRabring7 function as E3 ubiquitin ligase and mediates AlRab7 ubiquitination. Overexpression of AlRab7 and AlRabring7 independently and when co-transformed enhanced the growth of yeast cells during stress conditions. Further, the bimolecular fluorescence complementation assay shows the in planta interaction of the two proteins. Our results suggest that AlRab7 and AlRabring7 confers enhanced stress tolerance in yeast.

Functional Validation of JcWRKY2, a Group III Transcription Factor Toward Mitigating Salinity Stress in Transgenic Tobacco.

The plants being sessile cannot escape from the adverse environmental stresses, hence get negatively affected in terms of their growth and yield. Transcriptional control simultaneously regulate different cellular processes, minimizing the deleterious effects of these stresses. The salicylic acid (SA)-inducible WRKY family of transcription factors auto or crossregulate the stress signaling in response to abiotic and biotic stresses, facilitating enhanced stress tolerance. In this study, we characterized the group III WRKY gene, JcWRKY2 from ecological and economical valued shrub Jatropha curcas. The JcWRKY2 tobacco transgenics showed improved physiological growth parameters, elevated chlorophyll content, improved antioxidative activities, and increased endogenous SA with both salt and SA stress. Interestingly, the pretreatment with SA and hydrogen peroxide facilitated improved germination of transgenic seeds with salinity stress. The transgenics showed differential regulation of antioxidative enzymes, calcium/calmodulin, dehydrins, and phospholipase genes with salt and SA stress. The increased SA content in transgenics on stress treatments, enhanced the antioxidant capacity leading to reduced susceptibility to stresses. Thus, JcWRKY2 transgenics participate in SA-mediated, improved antioxidative status during salinity stress with reduced reactive oxygen species damage.

Deciphering hydrogen peroxide-induced signalling towards stress tolerance in plants.

Plants encounter a variety of adverse environmental conditions, such as high salinity, drought, extreme heat/cold and heavy metals contamination (abiotic stress) or attack of various pathogens (biotic stress). These detrimental environmental factors enhanced the ROS production such as singlet oxygen (1O2), superoxide (O2 •-), hydrogen peroxide (H2O2) and hydroxyl radicals (OH•). ROS are highly reactive and directly target several cellular molecules and metabolites, which lead to severe cellular dysfunction. Plants respond to oxidative damages by activating antioxidant machinery to trigger signalling cascades for stress tolerance. H2O2 signalling balances the plant metabolism through cross-talk with other signals and plant hormones during growth, development and stress responses. H2O2 facilitates the regulation of different stress-responsive transcription factors (TFs) including NAC, Zinc finger, WRKY, ERF, MYB, DREB and bZIP as both upstream and downstream events during stress signalling. The present review focuses on the biological synthesis of the H2O2 and its effect on the upregulation of kinase genes and stress related TFs for imparting stress tolerance.

The JcWRKY tobacco transgenics showed improved photosynthetic efficiency and wax accumulation during salinity.

Salinity is one of the major factors negatively affecting crop productivity. WRKY transcription factors (TFs) are involved in salicylic acid (SA) mediated cellular reactive oxygen species homeostasis in response to different stresses, including salinity. Therefore, the effect of NaCl, NaCl + SA and SA treatments on different photosynthesis-related parameters and wax metabolites were studied in the Jatropha curcas WRKY (JcWRKY) overexpressing tobacco lines. JcWRKY transgenics showed improved photosynthesis rate, stomatal conductance, intercellular CO2 concentration/ambient CO2 concentration ratio (Ci/Ca ratio), electron transport rate (ETR), photosynthesis efficiency (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of PSII electron transport (ΦPSII) in response to salinity stress, while exogenous SA application had subtle effect on these parameters. Alkane, the major constituent of wax showed maximum accumulation in transgenics exposed to NaCl. Other wax components like fatty alcohol, carboxylic acid and fatty acid were also higher in transgenics with NaCl + SA and SA treatments. Interestingly, the transgenics showed a higher number of open stomata in treated plants as compared to wild type (WT), indicating less perception of stress by the transgenics. Improved salinity tolerance in JcWRKY overexpressing tobacco transgenics is associated with photosynthetic efficiency and wax accumulation, mediated by efficient SA signalling. The transgenics showed differential regulation of genes related to photosynthesis (NtCab40, NtLhcb5 and NtRca1), wax accumulation (NtWIN1) and stomatal regulation (NtMUTE, NtMYB-like, NtNCED3-2 and NtPIF3). The present study indicates that JcWRKY is a potential TF facilitating improved photosynthesis with the wax metabolic co-ordination in transgenics during stress.

SbMYB15 transcription factor mitigates cadmium and nickel stress in transgenic tobacco by limiting uptake and modulating antioxidative defence system.

Plants require different inorganic minerals in an appropriate amount for growth; however, imbalance can limit growth and productivity. Heavy metal accumulation causes toxicity and generates signalling crosstalk with reactive oxygen species (ROS), phytohormones, genes and transcription factors (TFs). The MYB (myeloblastoma) TFs participate in plant processes such as metabolism, development, cell fate, hormone pathways and responses to stresses. This is the first report towards characterisation of R2R3-type MYB TF, SbMYB15, from succulent halophyte Salicornia brachiata Roxb. for heavy metal tolerance. The SbMYB15 showed >5-fold increased transcript expression in the presence of CdCl2 and NiCl2•6H2O. The constitutive overexpression of SbMYB15 conferred cadmium and nickel tolerance in transgenic tobacco, with improved growth and chlorophyll content. Further, the transgenics showed reduced generation of reactive oxygen species (H2O2 and O2•-) as compared with the wild-type (WT) with both Cd2+ and Ni2+ stress. Transgenics also showed low uptake of heavy metal ions, increased scavenging activity of the antioxidative enzymes (CAT and SOD) and higher transcript expression of antioxidative genes (CAT1 and MnSOD). Thus, the present study signifies that SbMYB15 can be deployed for developing heavy metal tolerance in crop plants via genetic engineering.