Tolerance Of Tobacco Research Articles

Group 3 LEA Protein, ZmLEA3, Is Involved in Protection from Low Temperature Stress.

Late embryogenesis abundant (LEA) proteins are a family of small highly hydrophilic proteins that accumulate at the onset of seed desiccation and in response to adverse conditions such as drought, salinity, low temperature, or water deficit. In previous studies, we demonstrated that ZmLEA3 could enhance the transgenic tobacco tolerance to osmotic and oxidative stresses. Here, we demonstrated that the transcription of ZmLEA3 in the maize stems could be significantly induced by low temperature and osmotic stresses and by treatment with abscisic acid (ABA) and H2O2. Further study indicated that ZmLEA3 is a single copy gene in the maize genome. The ZmLEA3 protein could protect lactate dehydrogenase (LDH) activity at low temperatures. The overexpression of ZmLEA3 conferred tolerance to low-temperature stress to transgenic tobacco, yeast (GS115) and E. coli (BL21).

Membrane-bound pyrophosphatase of human gut microbe Clostridium methylpentosum confers improved salt tolerance in Escherichia coli, Saccharomyces cerevisiae and tobacco.

Membrane-bound pyrophosphatases (PPases) are involved in the adaption of organisms to stress conditions, which was substantiated by numerous plant transgenic studies with H+-PPase yet devoid of any correlated evidences for other two subfamilies, Na+-PPase and Na+,H+-PPase. Herein, we demonstrate the gene cloning and functional evaluation of the membrane-bound PPase (CmPP) of the human gut microbe Clostridium methylpentosum. The CmPP gene encodes a single polypeptide of 699 amino acids that was predicted as a multi-spanning membrane and K+-dependent Na+,H+-PPase. Heterologous expression of CmPP could significantly enhance the salt tolerance of both Escherichia coli and Saccharomyces cerevisiae, and this effect in yeast could be fortified by N-terminal addition of a vacuole-targeting signal peptide from the H+-PPase of Trypanosoma cruzi. Furthermore, introduction of CmPP could remarkably improve the salt tolerance of tobacco, implying its potential use in constructing salt-resistant transgenic crops. Consequently, the possible mechanisms of CmPP to underlie salt tolerance are discussed.

ATP-Citrate Lyase Gene (SoACLA-1), a Novel ACLA Gene in Sugarcane, and Its Overexpression Enhance Drought Tolerance of Transgenic Tobacco

ATP-citrate lyase catalyzes cracking citrate to produce acetyl CoA in the cytoplasm and plays an important role in normal growth and development of plants. In this study, SoACLA-1 gene in sugarcane was cloned and characterized. The amino acid sequence of SoACLA-1 showed high homology with other ACLAs families, and they were clustered together in the phylogenetic tree. On transcript level, SoACLA-1 expressed strongly in root and stalk and responded to polyethylene glycol 6000, drought and ABA stresses. The results indicated that SoACLA-1 possibly involves in stress-responsive metabolic process. PCR analysis was performed to confirm the putative transgenic type in T1 tobacco plants. Overexpression of SoACLA-1 enhanced the tolerance of tobacco plants to drought. The sense transgenic tobacco plants were healthier, had longer roots and higher contents of relative water content and chlorophyll and activities of superoxide dismutase, peroxidase and catalase, but lower ion leakage and contents of malondialdehyde (MDA) and H2O2 than the wild-type and antisense transgenic plants under drought stress. In conclusion, SoACLA-1 plays an important role as a positive factor in drought stress response pathways and can be utilized for transformation to improve crop drought tolerance.

Overexpression of sugarcane gene SoSnRK2.1 confers drought tolerance in transgenic tobacco.

Overexpression of SoSnRK2.1 improved drought tolerance and growth of tobacco plants. Sucrose non-fermenting1-related protein kinase 2 (SnRK2) is a key enzyme in regulating ABA signal transduction in plants, and it plays a significant role in response to multiple abiotic stresses. In this research, SoSnRK2.1 gene was cloned from sugarcane variety GT21 and characterized under various stresses. The cloned SoSnRK2.1 gene has a complete open reading frame of 1002bp, encoding a peptide of 333 amino acids. The amino acid sequence of SoSnRK2.1 has high homology with those of Zea mays and Oryza sativa, which belongs to SnRK2s families. The expression of SoSnRK2.1 under stresses of drought, PEG, and ABA indicated that this gene is involved in stress responses in sugarcane. To investigate the gene function, fusional SoSnRK2.1-GFP-pBI121 under control of CaMV 35S was transformed into tobacco plants. Growth and morphology of transgenic plants demonstrated that overexpression of SoSnRK2.1 enhanced drought tolerance in tobacco. Transgenic tobacco plants had lower levels of ion leakage (IL), and contents of maleic dialdehyde (MDA) and H2O2, with higher activities of three antioxidant enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and chlorophyll and relative water content (RWC) than those in wide type (WT) tobacco. SoSnRK2.1 was stably transmitted to the next generation via sexual reproduction. Though the data presented here are from a heterologous system, it is highly likely that SoSnRK2.1 is involved in the abiotic stress response in sugarcane and may be playing an important role in regulation of its growth.

Simultaneous overexpression of CuZnSOD and cAPX from Arachis hypogaea leads to salinity stress tolerance in tobacco

Stress leads to generation of reactive oxygen species in living cells, which are scavenged by antioxidant enzymes. In the present study, genes encoding for two different antioxidant enzymes, namely cytosolic superoxide dismutase and cytosolic ascorbate peroxidase isolated from salt-tolerant cell lines of Arachis hypogaea, were simultaneously overexpressed in tobacco (Nicotiana tabacum cv. Xanthi) and the effect of their overexpression on alleviation of salinity stress was evaluated. The co-expression of AhCuZnSOD and AhcAPX in tobacco plants helped the resulting transgenic plants in overcoming salt stress. Compared to the wild-type plants, transgenic plants survived longer periods of salinity stress and displayed improved recovery after removal of the stress. The transgenic tobacco plants exhibited better photosynthetic efficiency, higher germination rate, more chlorophyll content, higher levels of total antioxidant enzyme activities, greater water retention capacity, higher proline accumulation, lower level of malondialdehyde content, and reactive oxygen species accumulation under stress conditions in comparison to the WT plants. Our analysis revealed that combined overexpression of the two antioxidant enzymes improved the salinity tolerance in transgenic plants.

Over-expression of poplar transcription factor ERF76 gene confers salt tolerance in transgenic tobacco

Ethylene response factors (ERFs) belong to a large plant-specific transcription factor family, which play a significant role in plant development and stress responses. Poplar ERF76 gene, a member of ERF TF family, can be up-regulated in response to salt stress, osmotic stress, and ABA treatment. The ERF76 protein was confirmed to be targeted preferentially in the nucleus of onion cell by particle bombardment. In order to understand the functions of ERF76 gene in salt stress response, we conducted temporal and spatial expression analysis of ERF76 gene in poplar. Then the ERF76 cDNA fragment containing an ORF was cloned from di-haploid Populus simonii×P. nigra and transferred into tobacco (Nicotiana tobacum) genome by Agrobacterium-mediated leaf disc method. Under salt stress, transgenic tobacco over-expressing ERF76 gene showed a significant increase in seed germination rate, plant height, root length, and fresh weight, as well as in relative water content (RWC), superoxide dismutase (SOD) activity, peroxidase (POD) activity, and proline content, compared to control tobacco lines. In contrast, transgenic tobacco lines displayed a decrease in malondialdehyde (MDA) accumulation, relative electrical conductivity (REC) and reactive oxygen species (ROS) accumulation in response to salt stress, compared to control tobacco lines. Over all, the results indicated that ERF76 gene plays a critical role in salt tolerance in transgenic tobacco.

Regulation of Galactolipid Biosynthesis by Overexpression of the Rice MGD Gene Contributes to Enhanced Aluminum Tolerance in Tobacco.

Membrane lipid alterations affect Al tolerance in plants, but little is known about the regulation of membrane lipid metabolism in response to Al stress. Transgenic tobacco (Nicotiana tabacum) overexpressing rice monogalactosyldiacylglycerol (MGDG) synthase (OsMGD) gene and wild-type tobacco plants were exposed to AlCl3, and the impact of Al toxicity on root growth, Al accumulation, plasma membrane integrity, lipid peroxidation and membrane lipid composition were investigated. Compared with the wild type, the transgenic plants exhibited rapid regrowth of roots after removal of Al and less damage to membrane integrity and lipid peroxidation under Al stress, meanwhile, the Al accumulation showed no difference between wild-type and transgenic plants. Lipid analysis showed that Al treatment dramatically decreased the content of MGDG and the ratio of MGDG to digalactosyldiacylglycerol (DGDG) in wild-type plants, while it was unchanged in transgenic plants. The stable of MGDG level and the ratio of MGDG/DGDG contribute to maintain the membrane stability and permeability. Moreover, Al caused a significant increase in phospholipids in wild-type plants, resulting in a high proportion of phospholipids and low proportion of galactolipids, but these proportions were unaffected in transgenic plants. The high proportion of phospholipids could contribute to a higher rate of Al3+ binding in the membrane and thereby leads to more membrane perturbation and damage. These results show that the regulation of galactolipid biosynthesis could play an important role in maintaining membrane structure and function under Al stress.

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.

Ectopic expression of phloem motor protein pea forisome PsSEO-F1 enhances salinity stress tolerance in tobacco.

PsSEOF-1 binds to calcium and its expression is upregulated by salinity treatment. PsSEOF - 1 -overexpressing transgenic tobacco showed enhanced salinity stress tolerance by maintaining cellular ion homeostasis and modulating ROS-scavenging pathway. Calcium (Ca(2+)) plays important role in growth, development and stress tolerance in plants. Cellular Ca(2+) homeostasis is achieved by the collective action of channels, pumps, antiporters and by Ca(2+) chelators present in the cell like calcium-binding proteins. Forisomes are ATP-independent mechanically active motor proteins known to function in wound sealing of injured sieve elements of phloem tissue. The Ca(2+)-binding activity of forisome and its role in abiotic stress signaling were largely unknown. Here we report the Ca(2+)-binding activity of pea forisome (PsSEO-F1) and its novel function in promoting salinity tolerance in transgenic tobacco. Native PsSEO-F1 promoter positively responded in salinity stress as confirmed using GUS reporter. Overexpression of PsSEO-F1 tobacco plants confers salinity tolerance by alleviating ionic toxicity and increased ROS scavenging activity which probably results in reduced membrane damage and improved yield under salinity stress. Evaluation of several physiological indices shows an increase in relative water content, electrolyte leakage, proline accumulation and chlorophyll content in transgenic lines as compared with null-segregant control. Expression of several genes involved in cellular homeostasis is perturbed by PsSEO-F1 overexpression. These findings suggest that PsSEO-F1 provides salinity tolerance through cellular Ca(2+) homeostasis which in turn modulates ROS machinery providing indirect link between Ca(2+) and ROS signaling under salinity-induced perturbation. PsSEO-F1 most likely functions in salinity stress tolerance by improving antioxidant machinery and mitigating ion toxicity in transgenic lines. This finding should make an important contribution in our better understanding of the significance of calcium signaling in phloem tissue leading to salinity stress tolerance.

Overexpression of Rosa rugosa anthocyanidin reductase enhances tobacco tolerance to abiotic stress through increased ROS scavenging and modulation of ABA signaling

Anthocyanidin reductase (ANR) is a key enzyme involved in the biosynthesis of proanthocyanidins (PAs) and plays a role in the plant stress response. However, the mechanism by which ANR confers stress tolerance in plants is not understood. Here, we report the isolation of RrANR, the homologous gene from rose, and NtABF, an ABA-response related transcription factor gene from tobacco. These genes were characterized regarding their functions in stress responses through the use of transgenic, transcriptomic and physiological analyses. Over-expression of RrANR in tobacco resulted in an increased accumulation of both PAs and abscisic acid (ABA), and also enhanced stress tolerance. Transcriptomic analysis of these transgenic tobacco lines indicated that RrANR overexpression induced global transcriptomic changes, including these involved in oxidation/reduction, hormone response and secondary metabolism. Genes related to ABA biosynthesis and reactive oxygen species (ROS)-scavenging were up-regulated in RrANR transgenic lines, and these effects were phenocopied by the direct treatment of tobacco plants with PAs and ABA. Transcriptomic data from each of these treatments identified the upregulation of a putative NtABF. Furthermore, the up-regulation of NtABF in RrANR transformants or in PAs- and ABA-treated tobacco plants was associated with enhanced stress tolerance. Overexpression of NtABF in transgenic tobacco mimicked the effects of RrANR-transgenic plants with regard to the up-regulation of ROS–scavenging genes and an increase in oxidative tolerance. Taken together, our findings indicate that overexpression of RrANR results in an increase in plant tolerance to oxidative stress via increased scavenging of ROS and modulation of the ABA signaling pathway.

Overexpression of the Maize psbA Gene Enhances Drought Tolerance Through Regulating Antioxidant System, Photosynthetic Capability, and Stress Defense Gene Expression in Tobacco.

The psbA (encoding D1 protein) plays an important role in protecting photosystem II (PSII) from oxidative damage in higher plants. In our previous study, the role of the psbA from maize (Zea mays. L) in response to SO2 stress was characterized. To date, information about the involvement of the psbA gene in drought response is scarce. Here we found that overexpression (OE) of ZmpsbA showed increased D1 protein abundance and enhanced drought stress tolerance in tobacco. The drought-tolerant phenotypes of the OE lines were accompanied by increases of key antioxidant enzymes SOD, CAT, and POD activities, but decreases of hydrogen peroxide, malondialdehyde, and ion leakage. Further investigation showed that the OE plants had much less reductions than the wild-type in the net photosynthesis rate (Pn), stomatal conductance (Gs), and the maximal photochemical efficiency of PSII (Fv/Fm) during drought stress; indicating that OE of ZmpsbA may alleviate photosynthesis inhibition during drought. qRT-PCR analysis revealed that there was significantly increased expression of NtLEA5, NtERD10C, NtAREB, and NtCDPK2 in ZmpsbA-OE lines. Together, our results indicate that ZmpsbA improves drought tolerance in tobacco possibly by alleviating photosynthesis reduction, reducing reactive oxygen species accumulation and membrane damage, and modulating stress defense gene expression. ZmpsbA could be exploited for engineering drought-tolerant plants in molecular breeding of crops.

Overexpression of IrlVHA-c, A Vacuolar-Type H+-ATPase c Subunit Gene from Iris lactea, Enhances Salt Tolerance in Tobacco

Vacuolar-type H+-ATPase (V-ATPase), a multi-subunit endomembrane proton pump, plays an important role in plant growth and response to environmental stresses. In the present study, transgenic tobacco that overexpressed the V-ATPase c subunit gene from Iris lactea (IrlVHA-c) was used to determine the function of IrlVHA-c. Quantitative PCR analysis showed that IrlVHA-c expression was induced by salt stress in I. lactea roots and leaves. Subcellular localization of green fluorescent protein (GFP) as marker combined with FM4-64 staining showed that the IrlVHA-c-GFP was localized to the endosomal compartment in tobacco cells. Compared with the wild-type, the IrlVHA-c transgenic tobacco plants exhibited greater seed germination rates, root length, fresh weight, and higher relative water content (RWC) of leaves under salt stress. Furthermore, the IrlVHA-c transgenic tobacco leaves have lower stomatal densities and larger stomatal apertures than wild-type. Under salt stress, superoxide dismutase (SOD) activity in the transgenic tobacco was significantly enhanced. Moreover, the level of malondialdehyde (MDA) in the transgenic tobacco was significantly lower than that in wild-type plants under salt stress. Taken together, these results suggested that the IrlVHA-c plays an important role in salt tolerance in transgenic tobacco by influencing stomatal movement and physiological changes.

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.

Enhanced salt tolerance of transgenic tobacco expressing a wheat salt tolerance gene

Soil salinity is one of the most important limiting factors of agricultural productivity in the world. The Triticum aestivum salt tolerance-related gene (TaSTRG) possesses a functional response to salt and drought stress conditions. A variety of stress factors, such as salt, drought, abscisic acid, and cold, may induce the expression of TaSTRG in wheat. In this study, the TaSTRG gene was transferred to tobacco via Agrobacterium-mediated transformation. Overexpression of TaSTRG in transgenic tobacco plants indicated higher salt tolerance and mediated more vigorous growth than in wild-type plants. Under salt stress conditions, the transgenic tobacco plants had higher germination and survival rates and longer root length than the control plants. Under salt treatments (200-250 mM), TaSTRG-overexpressing tobacco plants accumulated a higher amount of proline and had significantly lower malondialdehyde content than wild-type plants. Furthermore, transgene inheritance followed Mendelian laws, indicating the stability of TaSTRG in transgenic tobacco plants. These results indicated that the wheat TaSTRG gene plays an important role in responding to salt stress.

Hydrogen sulfide partly mediates abscisic acid-induced heat tolerance in tobacco (Nicotiana tabacum L.) suspension cultured cells

Abscisic acid (ABA), a plant hormone, plays crucial roles in plant growth, development and response to environmental stress. Recently, hydrogen sulfide (H2S) also has emerged similar functions, but interaction between ABA and H2S in the acquisition of heat tolerance is not clear. In this study, pretreatment of tobacco suspension cultured cells with ABA improved the survival percentage and regrowth ability, alleviated a decrease in cell vitality, increase in malondialdehyde content and electrolyte leakage of cells under heat stress, suggesting that ABA pretreatment could improve the heat tolerance of tobacco cells. In addition, treatment with ABA induced the accumulation of endogenous H2S in both tobacco cells and culture medium, increased the activity of l-cysteine desulfhydrase, a key enzyme in H2S biosynthesis. Also, ABA-induced heat tolerance was enhanced by addition of NaHS, a H2S donor, but weakened by dl-propargylglycine (specific inhibitor of H2S biosynthesis) and hypotaurine (H2S scavenger) respectively. These results suggest that ABA pretreatment could improve the heat tolerance of tobacco suspension cultured cells, and H2S, at least partly, mediated the acquisition of heat tolerance induced by ABA.

ITRAQ-based quantitative proteomic analysis reveals proteomic changes in leaves of cultivated tobacco (Nicotiana tabacum) in response to drought stress

Drought is one of the most severe forms of abiotic stresses that threaten the survival of plants, including crops. In turn, plants dramatically change their physiology to increase drought tolerance, including reconfiguration of proteomes. Here, we studied drought-induced proteomic changes in leaves of cultivated tobacco (Nicotiana tabacum), a solanaceous plant, using the isobaric tags for relative and absolute quantitation (iTRAQ)-based protein labeling technology. Of identified 5570 proteins totally, drought treatment increased and decreased abundance of 260 and 206 proteins, respectively, compared with control condition. Most of these differentially regulated proteins are involved in photosynthesis, metabolism, and stress and defense. Although abscisic acid (ABA) levels greatly increased in drought-treated tobacco leaves, abundance of detected ABA biosynthetic enzymes showed no obvious changes. In contrast, heat shock proteins (HSPs), thioredoxins, ascorbate-, glutathione-, and hydrogen peroxide (H2O2)-related proteins were up- or down-regulated in drought-treated tobacco leaves, suggesting that chaperones and redox signaling are important for tobacco tolerance to drought, and it is likely that redox-induced posttranslational modifications play an important role in modulating protein activity. This study not only provides a comprehensive dataset on overall protein changes in drought-treated tobacco leaves, but also shed light on the mechanism by which solanaceous plants adapt to drought stress.

ITRAQ protein profile analysis provides integrated insight into mechanisms of tolerance to TMV in tobacco (Nicotiana tabacum)

To further investigate the mechanism of the plant tolerance to tobacco mosaic virus (TMV) infection, tobacco NC89 (N) hypersensitive to TMV and its natural mutant Yuyan8 (Y) with tolerance to TMV were employed for differential accumulation proteome analysis. There were 260 specifically accumulated proteins in Yuyan8 after 24h inoculation (Yd), and the accumulations of 285 proteins inherent in Y have changed after TMV infection. Equally, there were 183 specifically accumulated proteins in NC89 after 24h inoculation (Nd), and 132 proteins inherent in N have changed after TMV infection. These differential proteins were respectively enriched in two pathways, of which photosynthesis pathway was the common pathway in two varieties. In photoreaction system, the accumulations of differential proteins, especially D1 protein, were not decreased in Yd compared to Nd. The results indicated that maintaining the stability of D1 protein and reasonable utilization of the energy was the essential for tolerance to TMV infection. It was also revealed that 14-3-3 protein and PR4 was specific expressed, and the expression of LRR was enhanced in Yd, suggesting that regulation of defense protein mediated by 14-3-3 protein quickly activated resistance system and enhanced the plant tolerance to TMV infection. SignificanceThis is the first work that the molecular basis of tobacco tolerance was discussed basic on proteomic investigation performed on wild type and its natural mutant. Our results lay the foundation for development of molecular breeding and further proteome research in tobacco.

MsZEP, a novel zeaxanthin epoxidase gene from alfalfa (Medicago sativa), confers drought and salt tolerance in transgenic tobacco.

The zeaxanthin epoxidase gene ( MsZEP ) was cloned and characterized from alfalfa and validated for its function of tolerance toward drought and salt stresses by heterologous expression in Nicotiana tabacum. Zeaxanthin epoxidase (ZEP) plays important roles in plant response to various environment stresses due to its functions in ABA biosynthetic and the xanthophyll cycle. To understand the expression characteristics and the biological functions of ZEP in alfalfa (Medicago sativa), a novel gene, designated as MsZEP (KM044311), was cloned, characterized and overexpressed in Nicotiana tabacum. The open reading frame of MsZEP contains 1992bp nucleotides and encodes a 663-amino acid polypeptide. Amino acid sequence alignment indicated that deduced MsZEP protein was highly homologous to other plant ZEP sequences. Phylogenetic analysis showed that MsZEP was grouped into a branch with other legume plants. Real-time quantitative PCR revealed that MsZEP gene expression was clearly tissue-specific, and the expression levels were higher in green tissues (leaves and stems) than in roots. MsZEP expression decreased in shoots under drought, cold, heat and ABA treatment, while the expression levels in roots showed different trends. Besides, the results showed that nodules could up-regulate the MsZEP expression under non-stressful conditions and in the earlier stage of different abiotic stress. Heterologous expression of the MsZEP gene in N. tabacum could confer tolerance to drought and salt stress by affecting various physiological pathways, ABA levels and stress-responsive genes expression. Taken together, these results suggested that the MsZEP gene may be involved in alfalfa responses to different abiotic stresses and nodules, and could enhance drought and salt tolerance of transgenic tobacco by heterologous expression.

Cytosolic ascorbate peroxidase and Cu, Zn-superoxide dismutase improve seed germination, plant growth, nutrient uptake and drought tolerance in tobacco

The effects of over-expression of two cytosolic antioxidant enzymes (Cu, Zn-SOD and/or APX) on plant nutrition, gas exchange, chlorophyll fluorescence, seed viability and germination in transgenic tobacco (Nicotiana tabacum cv. Xanthi) under deficit irrigation or salinity conditions were investigated. Three transgenic lines of tobacco were used in this study: line 17, harboring 2 copies of the cytosolic CuZn-SOD (cytsod) gene; line 51, with 2 copies of the cytosolic APX (cytapx) gene and line 39, harboring one copy of each gene. Over-expression of cytosolic antioxidants enzymes in tobacco plants resulted in a better growth performance that correlated with an improved photosynthetic capacity and nutrient uptake. Moreover, cytsod or cytapx genes promoted seed germination, and enhanced tolerance to mild water stress. In addition, this enhanced antioxidant capacity protected seeds from ageing during prolonged storage, and stimulated germination under salt stress conditions. These results suggest that cytosolic antioxidant transgenes are useful tools to improve drought tolerance, nutrient uptake and seed germination under stressful conditions.

SoMYB18, a sugarcane MYB transcription factor improves salt and dehydration tolerance in tobacco

MYB transcription factors play vital role in various biotic and abiotic defense responses. A differentially expressed, stress-responsive, R2-R3-type, MYB-like transcription factor-associated EST (MYB18) from drought and salt SSH libraries was identified. A full-length DNA sequence of a MYB gene, namely SoMYB18, was isolated from sugarcane var. Co740. SoMYB18 encodes for an ORF of 1284 bp having 427 amino acids with 47.43 kDa theoretical protein size MYB protein. The phylogenetic characterization of the deduced amino acid sequence showed similarity with monocot MYB proteins. SoMYB18 is a member of the R2R3-MYB subfamily, containing two MYB DNA-binding domains (R2, R3) and a SANT/MYB DNA-binding domain. The SoMYB18 gene was transferred into tobacco, and stable transgenic plants expressing SoMYB18 were evaluated for salt, drought and cold tolerance. Compared to un-transformed tobacco plants, SoMYB18-expressing plants exhibited notably improved tolerances to salt and drought stress. The SOD and CAT activities were considerably elevated in transgenic plants, as well as proline accumulation and chlorophyll content were considerably high and lipid peroxidation was reduced relative to un-transformed plants during salt stress. These results indicated that this sugarcane R2R3-MYB transcription factor plays key role in regulating stress responses and may be implicated in the activation of salt-related genes, being useful in improving the salt stress tolerance in crops.