Wheat expansin gene TaEXPA2 is involved in conferring plant tolerance to Cd toxicity.

Cadmium (Cd) is a severe and toxic heavy metal pollutant that affects plant growth and development. In this study, we found that the expression of an expansin gene, TaEXPA2, was upregulated in wheat leaves under CdCl2 toxicity. We characterized the involvement of TaEXPA2 in conferring Cd tolerance. Tobacco plants overexpressing TaEXPA2 showed higher germination rate, root elongation, and biomass accumulation compared to the wild-type (WT) plants upon CdCl2 treatment. The improved photosynthetic parameters and lesser cellular damage in transgenic plants exposed to Cd compared to that in the WT plants suggest that TaEXPA2 overexpression improves Cd tolerance in plants. Furthermore, we noticed that Cd was efficiently effluxed out of the cytoplasm in the transgenic plants owing to the enhanced activities of H+-ATPase, V-ATPase, and PPase, which helped in conferring Cd tolerance. Moreover, Cd concentration and ROS accumulation were lower in the transgenic plants than in WT plants as a consequence of enhanced antioxidant enzyme activities in the former. In addition, atexpa2, an Arabidopsis mutant, exhibited lower biomass and shorter primary root compared to its WT under Cd toxicity; however, the phenotype was recovered upon expression of TaEXPA2 in these mutants. Our results demonstrate that TaEXPA2 confers tolerance to Cd toxicity. The changed absorption/transportation of Cd and the antioxidative capacity may be involved in the improved tolerance of the transgenic plants with overexpression of TaEXPA2 to CdCl2 toxicity.

Overexpression of the wheat expansin gene TaEXPA2 improves oxidative stress tolerance in transgenic Arabidopsis plants.

Expansins play an important role in plant stress tolerance. In a previous study, we cloned the wheat expansin gene TaEXPA2. Here, we analyze its involvement in oxidative stress tolerance. First, we observed that the expression of TaEXPA2 in wheat seedlings was upregulated during H2O2 stress. Then, we assembled a TaEXPA2 gene expression vector, transformed it to Arabidopsis, and obtained transgenic plants overexpressing TaEXPA2 (labeled OE). When exposed to H2O2, both OE and wild-type (Col) plants were damaged by oxidative stress, as indicated by decolored leaves and increased malondialdehyde (MDA) content. Damage in OE plants was less severe than in Col plants (WT), and this was accompanied by higher activity of cell wall peroxidase (POD) enzymes, including soluble POD, ionically bound POD, and covalently bound POD. The expansin activities of the OE plants were also higher than WT under oxidative stress. We further obtained the Arabidopsis mutant atexpa2 (AtEXPA2 is homologous to TaEXPA2), and found that the antioxidant ability of atexpa2 was lower than that in Col plants, accompanied by depressed activity of POD enzymes and expansins in cell walls. We transformed wheat TaEXPA2 to atexpa2 and obtained plants (labeled Rs) capable of recovering the antioxidant capacity. Oxidative stress tolerance in Rs plants was higher than that of Col plants, and the Rs plants also had higher levels of cell wall POD enzyme and expansin activity. Finally, we identified 13 POD genes in Arabidopsis thaliana and analyzed their expression patterns using quantitative real-time PCR. The expression of 4 of these genes (AtPOD31, AtPOD33, AtPOD34 and AtPOD71) was significantly upregulated during exposure to H2O2. We speculate that the 4 genes upregulated by H2O2 treatment are involved in the increased activity of POD in the cell wall. We suggest that TaEXPA2 may regulate antioxidant capacity in plants by regulating the activity of cell wall peroxidase.

Wheat TaPUB1 modulates plant drought stress resistance by improving antioxidant capability.

E3 ligases play significant roles in plant stress tolerance by targeting specific substrate proteins for post-translational modification. In a previous study, we cloned TaPUB1 from Triticum aestivum L., which encodes a U-box E3 ligase. Real-time polymerase chain reaction revealed that the gene was up-regulated under drought stress. To investigate the function of TaPUB1 in the response of plants to drought, we generated transgenic Nicotiana benthamiana (N. benthamiana) plants constitutively expressing TaPUB1 under the CaMV35S promoter. Compared to wild type (WT), the transgenic plants had higher germination and seedling survival rates as well as higher photosynthetic rate and water retention, suggesting that the overexpression of TaPUB1 enhanced the drought tolerance of the TaPUB1 overexpressing (OE) plants. Moreover, less accumulation of reactive oxygen species (ROS) and stronger antioxidant capacity were detected in the OE plants than in the WT plants. To characterize the mechanisms involved, methyl viologen (MV) was used to induce oxidative stress conditions and we identified the functions of this gene in the plant tolerance to oxidative stress. Our results suggest that TaPUB1 positively modulates plant drought stress resistance potential by improving their antioxidant capacity.

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.

Ectopic expression of wheat expansin gene TaEXPA2 improved the salt tolerance of transgenic tobacco by regulating Na+ /K+ and antioxidant competence.

High salinity is one of the most serious environmental stresses that limit crop growth. Expansins are cell wall proteins that regulate plant development and abiotic stress tolerance by mediating cell wall expansion. We studied the function of a wheat expansin gene, TaEXPA2, in salt stress tolerance by overexpressing it in tobacco. Overexpression of TaEXPA2 enhanced the salt stress tolerance of transgenic tobacco plants as indicated by the presence of higher germination rates, longer root length, more lateral roots, higher survival rates and more green leaves under salt stress than in the wild type (WT). Further, when leaf disks of WT plants were incubated in cell wall protein extracts from the transgenic tobacco plants, their chlorophyll content was higher under salt stress, and this improvement from TaEXPA2 overexpression in transgenic tobacco was inhibited by TaEXPA2 protein antibody. The water status of transgenic tobacco plants was improved, perhaps by the accumulation of osmolytes such as proline and soluble sugar. TaEXPA2-overexpressing tobacco lines exhibited lower Na+ but higher K+ accumulation than WT plants. Antioxidant competence increased in the transgenic plants because of the increased activity of antioxidant enzymes. TaEXPA2 protein abundance in wheat was induced by NaCl, and ABA signaling was involved. Gene expression regulation was involved in the enhanced salt stress tolerance of the TaEXPA2 transgenic plants. Our results suggest that TaEXPA2 overexpression confers salt stress tolerance on the transgenic plants, and this is associated with improved water status, Na+ /K+ homeostasis, and antioxidant competence. ABA signaling participates in TaEXPA2-regulated salt stress tolerance.