Antisense Transgenic Plants Research Articles

Modulation of the Arabidopsis Starch Metabolic Network by the Cytosolic Acetyl-CoA Pathway in the Context of the Diurnal Illumination Cycle

The starch metabolic network was investigated in relation to other metabolic processes by examining a mutant with altered single-gene expression of ATP citrate lyase (ACL), an enzyme responsible for generating cytosolic acetyl-CoA pool from citrate. Previous research has shown that transgenic antisense plants with reduced ACL activity accumulate abnormally enlarged starch granules. In this study, we explored the underlying molecular mechanisms linking cytosolic acetyl-CoA generation and starch metabolism under short-day photoperiods. We performed transcriptome and quantification of starch accumulation in the leaves of wild-type and antisense seedlings with reduced ACL activity. The antisense-ACLA mutant accumulated more starch than the wild type under short-day conditions. Zymogram analyses were conducted to compare the activities of starch-metabolizing enzymes with transcriptomic changes in the seedling. Differential expression between wild-type and antisense-ACLA plants was detected in genes implicated in starch and acetyl-CoA metabolism, and cell wall metabolism. These analyses revealed a strong correlation between the transcript levels of genes responsible for starch synthesis and degradation, reflecting coordinated regulation at the transcriptomic level. Furthermore, our data provide novel insights into the regulatory links between cytosolic acetyl-CoA metabolism and starch metabolic pathways.

Cloning, functional characterization and evaluating potential in metabolic engineering for lavender ( +)-bornyl diphosphate synthase.

We isolated and functionally characterized a new ( +)-bornyl diphosphate synthase (( +)-LiBPPS) from Lavandula x intermedia. The in planta functions of ( +)-LiBPPS were evaluated in sense and antisense transgenic plants. The monoterpene ( +)-borneol contributes scent and medicinal properties to some plants. It also is the immediate precursor to camphor, another important determinant of aroma and medicinal properties in many plants. ( +)-Borneol is generated through the dephosphorylation of bornyl diphosphate (BPP), which is itself derived from geranyl diphosphate (GPP) by the enzyme ( +)-bornyl diphosphate synthase (( +)-BPPS). In this study we isolated and functionally characterized a novel ( +)-BPPS cDNA from Lavandula x intermedia. The cDNA excluding its transit peptide was expressed in E. coli, and the corresponding recombinant protein was purified with Ni-NTA agarose affinity chromatography. The recombinant ( +)-LiBPPS catalyzed the conversion of GPP to BPP as a major product, and a few minor products. We also investigated the in planta role of ( +)-LiBPPS in terpenoid metabolism through its overexpression in sense and antisense orientations in stably transformed Lavandula latifolia plants. The overexpression of ( +)-LiBPPS in antisense resulted in reduced production of ( +)-borneol and camphor without compromising plant growth and development. As anticipated, the overexpression of the gene led to enhanced production of borneol and camphor, although growth and development were severely impaired in most transgenic lines strongly and ectopically expressing the ( +)-LiBPPS transgene in sense. Our results demonstrate that LiBPPS would be useful in studies aimed at the production of recombinant borneol and camphor in vitro, and in metabolic engineering efforts aimed at lowering borneol and camphor production in plants. However, overexpression in sense may require a targeted expression of the gene in glandular trichomes using a trichome-specific promoter.

A Tomato Putative Metalloprotease SlEGY2 Plays a Positive Role in Thermotolerance

Intramembrane proteases play very important roles in plants, such as chloroplast development, flower morphology, and response to abiotic stress. In this study, a putative metalloprotease gene, homologous to Ethylene-dependent Gravitropism deficient and Yellow-green2 (EGY2) of Arabidopsis, was isolated from tomato (Solanum lycopersicum) plants and named SlEGY2. We found that SlEGY2 was a member of the metalloprotease family M50 which contained conserved motifs HEXXH and NPDG and was localized in the chloroplast. SlEGY2 antisense transgenic tomato plants (AS) have similar hypocotyls phenotype to the Arabidopsis egy2 mutant. Heat (42 °C), PEG, ABA and MeJA treatments can upregulate the expression of SlEGY2. Under heat stress, SlEGY2 AS lines are more sensitive, with more water loss (lower fresh weight), seriously damaged membrane, and ROS accumulation, but lower activities of APX and CAT. In addition, suppression of SlEGY2 decreases the content of chlorophyll and photosynthetic activities, especially photosystem II. These results suggest that SlEGY2 can regulate the thermotolerance of tomatoes by affecting ROS accumulation and photosynthetic activities.

Increased branching independent of strigolactone in cytokinin oxidase 2-overexpressing tomato is mediated by reduced auxin transport

Tomato production is influenced by shoot branching, which is controlled by different hormones. Here we produced tomato plants overexpressing the cytokinin-deactivating gene CYTOKININ OXYDASE 2 (CKX2). CKX2-overexpressing (CKX2-OE) plants showed an excessive growth of axillary shoots, the opposite phenotype expected for plants with reduced cytokinin content, as evidenced by LC-MS analysis and ARR5-GUS staining. The TCP transcription factor SlBRC1b was downregulated in the axillary buds of CKX2-OE and its excessive branching was dependent on a functional version of the GRAS-family gene LATERAL SUPPRESSOR (LS). Grafting experiments indicated that increased branching in CKX2-OE plants is unlikely to be mediated by root-derived signals. Crossing CKX2-OE plants with transgenic antisense plants for the strigolactone biosynthesis gene CAROTENOID CLEAVAGE DIOXYGENASE (CCD7-AS) produced an additive phenotype, indicating independent effects of cytokinin and strigolactones on increased branching. On the other hand, CKX2-OE plants showed reduced polar auxin transport and their bud outgrowth was reduced when combined with auxin mutants. Accordingly, CKX2-OE basal buds did not respond to auxin applied in the decapitated apex. Our results suggest that tomato shoot branching depends on a fine-tuning of different hormonal balances and that perturbations in the auxin status could compensate for the reduced cytokinin levels in CKX2-OE plants.

Metacaspase MC1 enhances aluminum-induced programmed cell death of root tip cells in Peanut

Metacaspases are cysteine-dependent proteases, which play essential roles in programmed cell death (PCD), and caspase-3-like protease is the crucial executioner. However, its response mechanism to aluminum (Al)-induced PCD is still elusive. Here, the type I metacaspase gene in peanut (Arachis hypoganea L.), AhMC1, was cloned from the Al-sensitive cultivar ZH2. Physiological and biochemical methods, as well as gene expression analyses, were employed to explore its function in Al-induced PCD in peanut root tips. AhMC1 had a 1068-bp open reading frame, encoding a peptide of 355 amino acids, and the purified protein exhibited a high caspase-3-like protease activity. Its expression levels in different tissues of peanut varieties ZH2 and 99–1507 (Al-tolerant) varied under Al-stress conditions. The subcellular localization indicated that AhMC1 was transferred from mitochondria into the cytoplasm. Furthermore, overexpressing AhMC1 reduced the resistance to Al stress. Sense transgenic plants showed a low relative root growth rate, and reduced superoxide dismutase, peroxidase, and catalase activities, compared with wild-type and antisense transgenic plants under Al-stress conditions, but had a high root-cell death rate, and increased Al and maleic dialdehyde contents. The data suggest that metacaspase AhMC1 is a positive factor in Al-induced PCD in peanut root tips.

Expression analysis of the polyphenol oxidase gene in response to signaling molecules, herbivory and wounding in antisense transgenic tobacco plants.

We provide evidence that the expression of the PPO gene was significantly reduced in response to wounding, MeJ and herbivory in transgenic tobacco under wound-inducible OsRGLP2 promoter in an anti-sense orientation. Polyphenol oxidase (PPO) genes play an important role in plant defense mechanisms against biotic and abiotic stresses. In the present study, a 655bp core sequence of the potato PPO gene was placed under the control of wound-inducible OsRGLP2 promoter in an anti-sense direction to evaluate its potential effects during biotic (Trialeurodes vaporariorum's infestation) and various abiotic (wounding, MeJ, ABA) stresses. Transcriptional profiling of PPO gene by real-time PCR (qRT-PCR) in transgenic tobacco revealed a significant suppression (3.5-fold) of PPO in response to wounding than control plants after 24h. In response to MeJ at different concentrations (100µM and 200µM), the PPO expression was greatly down-regulated by 4.7-fold after 6h at 100µM MeJ, and a non-significant expression was observed with ABA treatment. Moreover, significant levels of PPO reduction (sixfolds) was found in whitefly feeding assay indicating that expression of potato PPO in an anti-sense orientation had down-regulated the PPO activity. This down-regulation of PPO by wounding, MeJ and whitefly infestation clearly links the specific expression of PPO in biotic and abiotic stresses. In the future, PPO gene suppression in transgenic plants using anti-sense potato PPO gene construct can be used to inhibit enzymatic browning in fruits and vegetables, e.g., potato.

OsMAPK3 Phosphorylates OsbHLH002/OsICE1 and Inhibits Its Ubiquitination to Activate OsTPP1 and Enhances Rice Chilling Tolerance

Improvement of chilling tolerance is a major target in rice breeding. The signaling pathways regulating chilling consist of complex networks, including key transcription factors and their targets. However, it remains largely unknown how transcription factors are activated by chilling stress. Here, we report thatthe transcription factor OsbHLH002/OsICE1 is phosphorylated by OsMAPK3 under chilling stress. The osbhlh002-1 knockout mutant and antisense transgenic plants showed chilling hypersensitivity, whereas OsbHLH002-overexpressing plants exhibited enhanced chilling tolerance. OsbHLH002 can directly target OsTPP1, which encodes a key enzyme for trehalose biosynthesis. OsMAPK3 interacts with OsbHLH002 to prevent its ubiquitination by the E3 ligase OsHOS1. Under chilling stress, active OsMAPK3 phosphorylates OsbHLH002, leading to accumulation of phospho-OsbHLH002, which promotes OsTPP1 expression and increases trehalose content and resistance to chilling damage.Taken together, these results indicate that OsbHLH002 is phosphorylated by OsMAPK3, which enhances OsbHLH002 activation to its target OsTPP1 during chilling stress.

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.

Control of potato tuber dormancy and sprouting by expression of sense and antisense genes of pyrophosphatase in potato

Inorganic pyrophosphate (PPi) is an enzyme involved in sugar metabolism in potato tubers. In our previous study, we isolated an inorganic pyrophosphatase (PPase) gene from potato and obtained the transgenic potato plants transformed with the sense and antisense PPase genes respectively. In the present experiment, the physiological indexes, tuber dormancy, and sprouting characteristics of the transgenic potatoes were analyzed and evaluated. The result showed that the PPase activity and the inorganic phosphate content of tubers were lower in the antisense transgenic plant lines but were higher in the sense transgenic plant lines, compared with wild-type tubers. Soluble sugars, such as glucose, fructose and sucrose increased in transgenic plants that had overexpression of the sense PPase gene, but decreased in the antisense transgenic plant lines, compared with wild-type tubers. Tuber sprouting time of the antisense transgenic plants were delayed for 2 and 3 weeks and reached the 100 % sprouting rate only after 14 and 16 weeks storage compared with the wild-type when tubers are stored under 25 and 4 °C, respectively. In contrast, tuber sprouting time of the sense transgenic plants was earlier by approximately 2 weeks than that of wild-type tubers under these storage temperatures.

A homologue of vitamin K epoxide reductase in Solanum lycopersicum is involved in resistance to osmotic stress.

Vitamin K epoxide reductase (VKOR) exists widely in the chloroplasts of higher plants and plays important roles in redox regulation. However, investigations of plant VKOR function have primarily focused on VKOR from Arabidopsis, and knowledge concerning this function is therefore quite limited. In this study, Solanum lycopersicum was used to study the function of VKOR. Transcription level analysis revealed that SlVKOR (S. lycopersicum VKOR) expression was upregulated by salt or drought stress. To further investigate the function of SlVKOR in plants, we generated sense and antisense transgenic S. lycopersicum homozygotes at T2 generation plants. Compared with wild-type (WT) plants, the leaf disks of the SlVKOR overexpression plants retained a much higher percentage of chlorophyll after salt or drought treatment, whereas the antisense transgenic plants displayed an opposite response. The overexpressed plants displayed lower levels of H2O2 and superoxide anion radical (O2(·-)) than WT plants, whereas antisense plants accumulated considerably more H2O2 and O2(·-). The activities of reactive oxygen scavenger enzymes, including superoxide dismutase, peroxidase, ascorbate peroxidase and catalase, were consistent with the accumulation of reactive oxygen species. Based on these results, we suggest that SlVKOR is involved in resistance to salt or drought stress.

Molecular characterization and primary functional analysis of PeMPEC, a magnesium-protoporphyrin IX monomethyl ester cyclase gene of bamboo (Phyllostachys edulis).

A homologous gene of MPEC from Phyllostachys edulis was isolated and characterized. Its overexpression in Arabidopsis thaliana increased chlorophyll concentration and photosynthesis efficiency, indicating it is involved in chlorophyll biosynthesis. Magnesium-protoporphyrin IX monomethyl ester cyclase (MPEC) is an essential enzyme in the biosynthesis of chlorophyll, which plays an important role in photosynthesis. However, limited information is available on the roles of MPEC gene in bamboo. A homologous gene, PeMPEC was identified from Phyllostachys edulis, which comprised 1474bp and contained an open reading frame encoding 415 amino acids. PeMPEC was transcribed abundantly in leaf blade where photosynthesis predominantly occurs, which agreed with the protein accumulation pattern confirmed by Western blotting. The PeMPEC transcription was promoted by continuous darkness for 24h, and was suppressed by increasing light intensity (100-1500 µmo1m(-2)s(-1)) and high temperature (42°C). However, transcription was induced within 0.5h and thereafter declined with prolonged treatment (up to 12h) under low temperature (4°C). Although PeMPEC expressed weakly in etiolated leaves, transcript levels increased gradually with subsequent light treatment (200µmolm(-2)s(-1)). Overexpression of PeMPEC in Arabidopsis thaliana resulted in increased chlorophyll concentration and photosynthesis efficiency in sense transgenic plants compared with a reduction in antisense transgenic plants. These changes were consistent with the transcript levels of PeMPEC. These results indicated that PeMPEC might be involved in chlorophyll biosynthesis and play important roles in maintaining the stability of photosystems, and provide a basis for the study of chlorophyll biosynthesis and dissection of photosynthesis in bamboo.

Suppression of ASKβ (AtSK32), a Clade III Arabidopsis GSK3, Leads to the Pollen Defect during Late Pollen Development.

Arabidopsis Shaggy-like protein kinases (ASKs) are Arabidopsis thaliana homologs of glycogen synthase kinase 3/SHAGGY-like kinases (GSK3/SGG), which are comprised of 10 genes with diverse functions. To dissect the function of ASKβ (AtSK32), ASKβ antisense transgenic plants were generated, revealing the effects of ASKβ down-regulation in Arabidopsis. Suppression of ASKβ expression specifically interfered with pollen development and fertility without altering the plants’ vegetative phenotypes, which differed from the phenotypes reported for Arabidopsis plants defective in other ASK members. The strength of these phenotypes showed an inverse correlation with the expression levels of ASKβ and its co-expressed genes. In the aborted pollen of ASKβ antisense plants, loss of nuclei and shrunken cytoplasm began to appear at the bicellular stage of microgametogenesis. The in silico analysis of promoter and the expression characteristics implicate ASKβ is associated with the expression of genes known to be involved in sperm cell differentiation. We speculate that ASKβ indirectly affects the transcription of its co-expressed genes through the phosphorylation of its target proteins during late pollen development.

Decreased TK activity alters growth, yield and tolerance to low temperature and low light intensity in transgenic cucumber plants.

Four CsTK antisense transgenic cucumber plants were obtained. Decreased TK activity decreased the photosynthetic rate, seed germination rate, growth yield, and the tolerance to low temperature and weak light stress. Transketolase (TK, EC 2.2.1.1) is a key enzyme in the photosynthetic carbon reduction cycle (Calvin cycle). A cDNA fragment (526 bp) encoding transketolase was cloned from cucumber plants (Cucumis sativa L. cv 'Jinyou 3') by RT-PCR. The antisense expression [(PBI-CsTK(-)] vector containing the CsTK gene fragment was constructed. The resulting plasmid was introduced into the cucumber inbred lines '08-1' using the agrobacterium-mediated method, and four antisense transgenic cucumber plants were obtained. Decreased CsTK expression either unaltered or slightly increased the mRNA abundance and activities of the other main enzymes in the Calvin cycle, however, it decreased the TK activity and net photosynthetic rate (Pn) in antisense transgenic cucumber leaves. Antisense plants showed decreases in the growth, ratio of female flowers and yield compared with the wild-type (WT) plants. The decrease in Pn, stomatal conductance (Gs), transpiration rate (Tr), photochemical efficiency (Fv/Fm) and actual photochemical efficiency of PSII (ΦPSII) and the increase in electrolyte leakage (EL) were greater in antisense transgenic plants than in WT plants under low temperature (5 °C) and low light intensity (100 μmol m(-2) s(-1)).

Aluminum-induced programmed cell death promoted by AhSAG, a senescence-associated gene in Arachis hypoganea L.

Programmed cell death (PCD) is a foundational cellular process in plant development and elimination of damaged cells under environmental stresses. In this study, Al induced PCD in two peanut (Arachis hypoganea L.) cultivars Zhonghua 2 (Al-sensitive) and 99-1507 (Al-tolerant) using DNA ladder, TUNEL detection and electron microscopy. The concentration of Al-induced PCD was lower in Zhonghua 2 than in 99-1507. AhSAG, a senescence-associated gene was isolated from cDNA library of Al-stressed peanut with PCD. Open reading frame (ORF) of AhSAG was 474bp, encoding a SAG protein composed of 157 amino acids. Compared to the control and the antisense transgenic tobacco plants, the fast development and blossom of the sense transgenic plants happened to promote senescence. The ability of Al tolerance in sense transgenic tobacco was lower than in antisense transgenic tobacco according to root elongation and Al content analysis. The expression of AhSAG-GFP was higher in sense transgenic tobacco than in antisense transgenic tobacco. Altogether, these results indicated that there was a negative relationship between Al-induced PCD and Al-resistance in peanut, and the AhSAG could induce or promote the occurrence of PCD in plants

Antisense-mediated depletion of tomato GDP-l-galactose phosphorylase increases susceptibility to chilling stress

The GDP-l-galactose phosphorylase (GGP), which converts GDP-l-galactose to l-Gal-1-phosphate, is generally considered to be a key enzyme of the major ascorbate biosynthesis pathways in higher plants, but experimental evidence for its role in tomato is lacking. In the present study, the GGP gene was isolated from tomato (Solanum lycopersicum) and transient expression of SlGGP-GFP (green fluorescent protein) fusion protein in onion cells revealed the cytoplasmic and nucleus localization of the protein. Antisense transgenic tomato lines with only 50–75% ascorbate level of the wild type (WT) were obtained. Chilling treatment induced lower increase in AsA levels and redox ratio of ascorbate in antisense transgenic plants compared with WT plants. Under chilling stress, transgenic plants accumulated more malendialdehyde (MDA) and more O2−, leaked more electrolytes and showed lower maximal photochemical efficiency of PSII (Fv/Fm), net photosynthetic rate (Pn), and oxidizable P700 compared with WT plants. Furthermore, the antisense transgenic plants exhibited significantly higher H2O2 level and lower ascorbate peroxidase (APX) activity. Our results suggested that GGP plays an important role in protecting plants against chilling stress by maintaining ascorbate pool and ascorbate redox state.

Antisense-mediated depletion of GMPase gene expression in tobacco decreases plant tolerance to temperature stresses and alters plant development

In our previous work [1] we investigated the role of tomato GDP-mannose pyrophosphorylase (EC 2.7.7.22) in plants by overexpressing its gene in tobacco leaves and showed its function in AsA metabolism and detoxification of reactive oxygen species under temperature stresses. In this study, we use the antisense technique to block the endogenous GMPase gene expression in tobacco in order to further investigate its function. Northern and western blot analysis confirmed that the expression of endogenous tobacco GMPase mRNA and protein was inhibited by this antisense expression. Consequently, the activity of GMPase and the content of AsA in the leaves of antisense transgenic plants were markedly decreased. This was also the case for the activities of both chloroplastic SOD (superoxide dismutase EC 1.15.1.1), APX (ascorbate peroxidase EC 1.11.1.7) and the content of AsA in leaves of the transgenic plants. On the contrary, the contents of H(2)O(2) and O(2) (-•) were increased. Meanwhile, the net photosynthetic rate (Pn) and the maximal photochemical efficiency of PSII (Fv/Fm) also declined in the leaves of antisense plants. Under high or low temperature stresses, the seed germination rate of the antisense transgenic plants was significantly decreased in comparison with that of the wild-type tobacco. Interestingly, the antisense plants had smaller leaves and an earlier onset of flowering. In conclusion, the depletion of GMPase decreased the content of AsA, resulting in the plants susceptible to the oxidative damage caused by temperature stresses and subjected to developmental alternations.

Constitutive accumulation of zeaxanthin in tomato alleviates salt stress‐induced photoinhibition and photooxidation

Zeaxanthin (Z) has a role in the dissipation of excess excitation energy by participating in non-photochemical quenching (NPQ) and is essential in protecting the chloroplast from photooxidative damage. To investigate the physiological effects and functional mechanism of constitutive accumulation of Z in the tomato at salt stress-induced photoinhibition and photooxidation, antisense-mediated suppression of zeaxanthin epoxidase transgenic plants and the wild-type (WT) tomato were used. The ratio of Z/(V + A + Z) and (Z + 0.5A)/(V + A + Z) in antisense transgenic plants were maintained at a higher level than in WT plants under salt stress, but the value of NPQ in WT and transgenic plants was not significantly different under salt stress. However, the maximal photochemical efficiency of PSII (Fv/Fm) and the net photosynthetic rate (Pn) in transgenic plants decreased more slowly under salt stress. Furthermore, transgenic plants showed lower level of hydrogen peroxide (H(2)O(2)), superoxide anion radical (O(2)(•-)) and ion leakage, lower malondialdehyde content. Compared with WT, the content of D1 protein decreased slightly in transgenic plants under salt stress. Our results suggested that the constitutive accumulation of Z in transgenic tomatoes can alleviate salt stress-induced photoinhibition because of the antioxidant role of Z in the scavenging quenching of singlet oxygen and/or free radicals in the lipid phase of the membrane.

Antisense-mediated suppression of tomato thylakoidal ascorbate peroxidase influences anti-oxidant network during chilling stress

Photosynthesis is a well-established source of reactive oxygen species (ROS) in plants particularly under chilling stress. Ascorbate peroxidase (APXs) plays an important role in the anti-oxidant system by utilizing AsA as specific electron donor to reduce H(2)O(2) to water. In order to investigate the possible mechanisms of ascorbate peroxidsae (APX) in photoprotection under chilling stress, a tomato (Lycopersicon esculentum Mill.) thylakoidal ascorbate peroxidase gene (LetAPX) was isolated and antisense transgenic tomato plants were produced. Under chilling stress, transgenic plants accumulated more H(2)O(2), and showed higher levels of ion leakage and malondialdehyde (MDA), lower net photosynthetic rate (Pn), lower maximal photochemical efficiency of PSII (Fv/Fm) and less content of D1 protein compared with wild type (WT) plants. On the other hand, after chilling stress, transgenic plants showed higher reduced ascorbate (AsA) and activities of catalase (CAT) and superoxide dismutase (SOD) than those in WT plants, and the expression of several known stress-responsive and antioxidative genes was also higher at the end of chilling treatment. These results suggested that the suppression of LetAPX gene induced compensatory anti-oxidant mechanisms in tomato, and inactivation of tAPX may have a regulatory role in facilitating redox signaling pathways under chilling stress. Furthermore, transient increases in ROS levels also have a vital role in stress signaling and thereby in the survival of plants under chilling conditions.

Transgenic tomato plants overexpressing chloroplastic monodehydroascorbate reductase are resistant to salt- and PEG-induced osmotic stress

RNA gel hybridization showed that the expression of monodehydroascorbate reductase (MDHAR) in the wild type (WT) tomato was decreased firstly and then increased under salt- and polyethylene glycol (PEG)-induced osmotic stress, and the maximum level was observed after treatment for 12 h. WT, sense transgenic and antisense transgenic tomato plants were used to analyze the antioxidative ability to cope with osmotic stresses. After salt stress, the fresh mass (FM) and height of sense transgenic lines were greater than those of antisense lines and WT plants. Under salt and PEG treatments, sense transgenic plants showed a lower level of hydrogen peroxide (H2O2) and malondialdehyde (MDA), a higher net photosynthetic rate (P N), and the maximal photochemical efficiency of PSII (Fv/Fm) compared with WT and antisense transgenic plants. Moreover, sense lines maintained higher ascorbate peroxidase (APX) activity than WT and antisense plants under salt- and PEG-induced osmotic stress. These results indicate that chloroplastic MDHAR plays an important role in alleviating photoinhibition of PSII by elevating ascorbate (AsA) level under salt- and PEG-induced osmotic stress.

Manipulation of monoubiquitin improves salt tolerance in transgenic tobacco

Ubiquitin (Ub) is regarded as a stress protein involved in many stress responses. In this paper, sense and antisense transgenic tobacco plants, as well as the wild type and vector control, were used to study the role of Ub in salt tolerance of plants. In sense Ta-Ub2 transgenic tobacco plants, there was higher expression of Ub protein conjugates than in the wild type and vector control, but the reverse trend was observed in antisense Nt-Ub1 transgenic plants. The germination rate of tobacco seed, growth status and photosynthesis of the tobacco plants suggested that over-expressing Ub promoted the growth of transgenic tobacco plants and enhanced their salt tolerance, but the opposite effect was seen in plants with repressed Ub expression. Changes in antioxidant capacity may be one of the mechanisms underlying Ub-regulated salt tolerance. Furthermore, improved tolerance to a combination of stresses was also observed in the sense transgenic tobacco plants. These findings imply that Ub is involved in the tolerance of plants to abiotic stress.