Increased gibberellin contents contribute to accelerated growth and development of transgenic tobacco overexpressing a wheat ubiquitin gene

Genome-wide analysis and identification of TaRING-H2 gene family and TaSDIR1 positively regulates salt stress tolerance in wheat

Salt stress is an abiotic stress factor that limits high yields, and thus identifying salt tolerance genes is very important for improving the tolerance of salt in wheat. In this study we identified 274 TaRING-H2 family members and analyzed their gene positions, gene structures, conserved structural domains, promoter cis-acting elements and covariance relationships. And we investigated TaRING-H2-120 (TaSDIR1) in salt stress. Transgenic lines exhibited higher salt tolerance in the germination and seedling stages. Compared with the wild type, overexpression of TaSDIR1 upregulated the expression of genes encoding enzymes related to the control of reactive oxygen species (ROS), thereby reducing the accumulation of ROS, as well as increased the expression of ion transport-related genes to limit the inward flow of Na⁺ in vivo and maintain a higher K⁺/Na⁺ ratio. The expression levels of these genes were opposite in lines where TaSDIR1 was silenced by BSMV-VIGS, and the silenced wheat exhibited higher salt sensitivity. Arabidopsis mutants and heterologous TaSDIR1 overexpressing lines had similar salt stress tolerance phenotypes. We also demonstrated that TaSDIR1 interacted with TaSDIR1P2 in vivo and in vitro. A sequence of 80-100 amino acids in TaSDIR1P2 encoded a coiled coil domain that was important for the activity of E3 ubiquitin ligase, and it was also the core region for the interaction between TaSDIR1 and TaSDIR1P2. Overall, our results suggest that TaSDIR1 positively regulates salt stress tolerance in wheat.

An R2R3-MYB transcription factor VyMYB24, isolated from wild grape Vitis yanshanesis J. X. Chen., regulates the plant development and confers the tolerance to drought

In grapevines, the MYB transcription factors play an important regulatory role in the phenylpropanoid pathway including proanthocyanidin, anthocyanin, and flavonoid biosynthesis. However, the role of MYB in abiotic stresses is not clear. In this study, an R2R3-MYB transcription factor, VyMYB24, was isolated from a high drought-tolerant Chinese wild Vitis species V. yanshanesis. Our findings demonstrated that it was involved in plant development and drought tolerance. VyMYB24 is a nuclear protein and is significantly induced by drought stress. When over-expressed in tobacco, VyMYB24 caused plant dwarfing including plant height, leaf area, flower size, and seed weight. The GA1+3 content in transgenic plants was reduced significantly, and spraying exogenous gibberellin could recover the dwarf phenotype of VyMYB24 transgenic plants, suggesting that VyMYB24 might inhibit plant development by the regulation of gibberellin (GA) metabolism. Under drought stress, the VyMYB24 transgenic plants improved their tolerance to drought with a lower wilting rate, lower relative electrical conductivity, and stronger roots. Compared to wild-type tobacco plants, VyMYB24 transgenic plants accumulated less reactive oxygen, accompanied by increased antioxidant enzyme activity and upregulated gene expression levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) genes. In addition, transgenic plants accumulated more proline, and their related synthetic genes NtP5CR and NtP5CS genes were significantly upregulated when exposed to drought. Besides, abiotic stress-responsive genes, NtDREB, NtERD10C, NtERD10D, and NtLEA5, were upregulated significantly in VyMYB24 transgenic plants. These results indicate that VyMYB24 plays a positive regulatory role in response to drought stress and also regulates plant development, which provides new evidence to further explore the molecular mechanism of drought stress of the MYB gene family.

An F-box protein from wheat, TaFBA-2A, negatively regulates JA biosynthesis and confers improved salt tolerance and increased JA responsiveness to transgenic rice plants

Soil salinity is a serious problem encountered by agriculture worldwide, which will lead to many harmful effects on plant growth, development, and even crop yield. F-box protein is the core subunit of the Skp1-Cullin-F-box (SCF) complex E3 ligase and plays crucial roles in regulating the growth, development, biotic & abiotic stresses, as well as hormone signaling pathway in plants. In this study, an FBA type F-box gene TaFBA-2A was isolated from wheat (Triticum aestivum L.). This study showed that TaFBA-2A could interact with TaSKP1, and TaOPR2, the crucial enzyme involving in jasmonic acid (JA) biosynthesis. TaFBA-2A negatively regulates JA biosynthesis, probably by mediating the degradation of TaOPR2 via the ubiquitin-26S proteasome pathway. Ectopic expression of TaFBA-2A improved the salt tolerance and increased the JA responsiveness of the transgenic rice lines. In addition, some agronomic traits closely related to crop yield were significantly enhanced in the rice lines ectopic expressing TaFBA-2A. The data obtained in this study shed light on the function and mechanisms of TaFBA-2A in JA biosynthesis and the responses to salt stress and JA treatment; this study also suggested that TaFBA-2A has the potential in improving the salt tolerance and crop yield of transgenic rice plants.

The wheat E3 ligase TaPUB26 is a negative regulator in response to salt stress in transgenic Brachypodium distachyon

Various abiotic stresses, including high salinity, affect the growth and yield of crop plants. We isolated a gene, TaPUB26, from wheat that encodes a protein containing a U-box domain and armadillo (ARM) repeats. The TaPUB26 transcript levels were upregulated by high salinity, temperature, drought and phytohormones, suggesting the involvement of TaPUB26 in abiotic stress responses. An in vitro ubiquitination assay revealed that TaPUB26 is an E3 ubiquitin ligase. We overexpressed TaPUB26 in Brachypodium distachyon to evaluate TaPUB26 regulation of salt stress tolerance. Compared with the wild type (WT) line, the overexpression lines showed higher salt stress sensitivity under salt stress conditions, but lower chlorophyll (Chl) content, lower photosynthetic levels and overall reduced salt stress tolerance. Additionally, the transgenic plants showed more severe membrane damage, lower antioxidant enzyme activity and more reactive oxygen species (ROS) accumulation than WT plants under salt stress, which might be related to the changes in the expression levels of some antioxidant genes. In addition, the transgenic plants also had higher Na⁺ and lower K⁺ contents, thus maintaining a higher cytosolic Na⁺/K⁺ ratio in leaves and roots than that in WT plants. Further analysis of the molecular mechanisms showed that TaPUB26 interacted with TaRPT2a, an ATPase subunit of the 26S proteasome complex in wheat. We speculated that TaPUB26 negatively regulates salt stress tolerance by interacting with other proteins, such as TaRPT2a, and that this mechanism involves altered antioxidant competition and cytosolic Na⁺/K⁺ equilibrium.

NbGIS regulates glandular trichome initiation through GA signaling in tobacco

KEY MESSAGE

A novel gene NbGIS positively regulates glandular trichome initiation through GA Signaling in tobacco. NbMYB123-like regulates glandular trichome initiation by acting downstream of NbGIS in tobacco. Glandular trichome is a specialized multicellular structure which has capability to synthesize and secrete secondary metabolites and protects plants from biotic and abiotic stresses. Our previous results revealed that a C2H2 zinc-finger transcription factor GIS and its sub-family genes act upstream of GL3/EGL3-GL1-TTG1 transcriptional activator complex to regulate trichome initiation in Arabidopsis. In this present study, we found that NbGIS could positively regulate glandular trichome development in Nicotiana benthamiana (tobacco). Our result demonstrated that 35S:NbGIS lines exhibited much higher densities of trichome on leaves, main stems, lateral branches and sepals than WT plants, while NbGIS:RNAi lines had the opposite phenotypes. Furthermore, our results also showed that NbGIS was required in response to GA signal to control glandular trichome initiation in Nicotiana benthamiana. In addition, our results also showed that NbGIS significantly influenced GA accumulation and expressions of marker genes of the GA biosynthesis, might result in the changes of growth and maturation in tobacco. Lastly, our results also showed that NbMYB123-like regulated glandular trichome initiation in tobacco by acting downstream of NbGIS. These findings provide new insights to discover the molecular mechanism by which C2H2 transcriptional factors regulates glandular trichome initiation through GA signaling pathway in tobacco.

Wheat F-Box Protein Gene TaFBA1 Is Involved in Plant Tolerance to Heat Stress

Adverse environmental conditions, including high temperature, often affect the growth and production of crops worldwide. F-box protein, a core component of the Skp1-Cullin-F-box (SCF) E3 ligase complex, plays an important role in abiotic stress responses. A previously cloned gene from wheat, TaFBA1, encodes a homologous F-box protein. A Yeast two-Hybrid (Y2H) assay showed that TaFBA1 interacted with other SCF proteins. We found that the expression of TaFBA1 could be induced by heat stress (45°C). Overexpression of TaFBA1 enhanced heat stress tolerance in transgenic tobacco, because growth inhibition was reduced and photosynthesis increased as compared with those in the wild type (WT) plants. Furthermore, the accumulation of H₂O₂, O₂^-, and carbonyl protein decreased and cell damage was alleviated in transgenic plants under heat stress, which resulted in less oxidative damage. However, the transgenic plants contained more enzymatic antioxidants after heat stress, which might be related to the regulation of some antioxidant gene expressions. The qRT-PCR analysis showed that the overexpression of TaFBA1 upregulated the expression of genes involved in reactive oxygen species (ROS) scavenging, proline biosynthesis, and abiotic stress responses. We identified the interaction of TaFBA1 with Triticum aestivum stress responsive protein 1 (TaASRP1) by Y2H assay and bimolecular fluorescence complementation (BiFC) assay. The results suggested that TaFBA1 may improve enzymatic antioxidant levels and regulate gene expression by interacting with other proteins, such as TaASRP1, which leads to the enhanced heat stress tolerance seen in the transgenic plants.

Heterologous expression of wheat TaRUB1 gene enhances disease resistance in Arabidopsis thaliana

Expression of TaRUB1 gene in Arabidopsis thaliana elevates the level of disease-related genes in response to pathogen invasion through the accumulation of callose, necrotic cells, and the outbreak of ROS. Ubiquitin (Ub) and ubiquitin-like proteins are highly conserved in sequence and can covalently bind and modify many intracellular proteins which can be recognized and degraded by 26S proteasome. Post-translational modification of proteins has become a hot research spot today. In the previous study, a cDNA of related-to-ubiquitin protein belonged to ubiquitin-like proteins, whose spatial structure comprised Ub and NEDD8, was obtained from wheat SN6306 by suppression-subtractive hybridization and was named TaRUB1. TaRUB1 is induced by wheat powdery mildew and significantly upregulated in resistant wheat SN6306. In this study, heterologous expression of TaRUB1 in A. thaliana was used to study the function of this gene in response to pathogen Pseudomonas syringae pv. Tomato DC3000 (Pst DC3000). Transgenic A. thaliana showed relatively fewer disease symptoms, accompanied by common inhibition of living body parasitic defense responses, accumulation of more callose and reactive oxygen species (ROS), and concentrated cell death, simultaneously antioxidant enzyme activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase were higher than those in wild-type (WT) plant after infection with Pst DC3000. Meanwhile, hypersensitive cell death, which was possibly ROS burst, was also observed in transgenic A. thaliana. By quantitative reverse transcription-polymerase chain reaction analysis, some marker genes for hypersensitive response showed significantly higher transcriptional expression level in transgenic A. thaliana, which activates system-acquired resistance, than that of WT plants. Heterologous expression of TaRUB1 can significantly enhance resistance to Pst DC3000 in A. thaliana, suggesting that TaRUB1 is related to plant disease resistance.

The improvement of salt tolerance in transgenic tobacco by overexpression of wheat F-box gene TaFBA1

F-box protein is a major subunit of the Skp1-Cullin-F-box (SCF) complex. We previously isolated an F-box gene from wheat, TaFBA1, and here we show that overexpression of TaFBA1 in transgenic plants under salt stress increases germination rate, root elongation, and biomass accumulation compared with WT plants. Improvements in the photosynthetic rate and its corresponding parameters were also found in the transgenic plants. These results suggest that overexpression of TaFBA1 improves salt stress tolerance in transgenic tobacco. Further, the transgenic plants displayed less membrane damage, higher antioxidant enzyme activity, and less accumulation of ROS under salt stress. The transgenic plants also had lower Na+ content and higher K+ content than WT plants in leaves and roots. The activity of H+-ATPase on the plasma membrane in the transgenic plants was higher than in WT plants, and was accompanied by a net Na+ efflux. In the tonoplast, the activity levels of V-ATPase and PPase were also higher in the transgenic plants, thus helping to maximize intracellular Na+ compartmentalization. The expression of some stress-related genes was upregulated by salt stress. This suggests that the enhancement of plant salt stress tolerance may be associated with an improvement in antioxidative competition and Na+/K+ ion regionalization.

Overexpression of wheat ubiquitin gene, Ta-Ub2, improves abiotic stress tolerance of Brachypodium distachyon

Ubiquitination plays an important role in regulating plant's development and adaptability to abiotic stress. To investigate the possible functions of a wheat monoubiquitin gene Ta-Ub2 in abiotic stress in monocot and compare it with that in dicot, we generated transgenic Brachypodium plants overexpressing Ta-Ub2 under the control of CaMV35s and stress-inducible RD29A promoters. The constitutive expression of Ta-Ub2 displayed slight growth inhibition in the growth of transgenic Brachypodium distachyon under the control conditions. However, this inhibition was minimized by expression of Ta-Ub2 under the control of stress-inducible RD29A promoter. Compared with WT, the transgenic plants preserved more water and showed higher enzymatic antioxidants under drought stress, which might be related to the change in the expression of some antioxidant genes. The expression of C-repeat binding factors transcription factor genes in the transgenic B. distachyon lines were upregulated under water stress. Salt and cold tolerances of transgenic B. distachyon were also improved. Although the phenotypic changes in the transgenic plants were different, overexpression of Ta-Ub2 improved the abiotic stress tolerance in both dicot and monocot plants. The improvement in Ta-Ub2 transgenic plants in abiotic stress tolerance might be, at least partly, through regulating the gene expression and increasing the enzymatic antioxidants.

Determination of gibberellins in soybean using tertiary amine labeling and capillary electrophoresis coupled with electrochemiluminescence detection

A novel sensitive method based on tertiary amine labeling for the analysis of gibberellins (GAs) by capillary electrophoresis (CE) coupled with electrochemiluminescence (ECL) detection was proposed. GA3 was tagged with 2-(2-aminoethyl)-1-methylpyrrolidine (AEMP) using N, N'-dicyclohexylcarbodiimide (DCC) and 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HOOBt) as coupling agents in acetonitrile to produce GA3-AEMP-derivative. The GA3-AEMP-derivative was injected into CE by electrokinetic injection and detected by Ru(bpy)3(2+)-based ECL. The parameters affecting derivatization, detection and separation such as concentration of reactants, detection potential, pH and concentration of separation buffer, were investigated in detail. Under optimum conditions, the linear concentration range for GA3 was from 2.0×10(-7) to 1.28×10(-4)M with a correlation coefficient of 0.9997. The detection limit was 8×10(-8)M (S/N=3). The relative standard deviations of migration time, peak intensity and peak area for nine continuous injections of 2.0×10(-5)M GA3-AEMP-derivative were 1.0%, 2.1% and 4.2%, respectively. The developed approach was successfully applied to the determination of total GAs in the stem, leaf and seed of soybean (Glycine max [L.] Merr.) with recoveries in the range from 89.6% to 99.3%.