Overexpression of ethylene response factor ERF96 gene enhances selenium tolerance in Arabidopsis.

Ethylene response factors (ERFs) are involved in the regulation of plant responses to biotic and abiotic stresses. Here we provide evidence for a role of ERF96, a member of the ERF transcription factor group IX, in selenite tolerance in Arabidopsis. ERF96 gene was rapidly up-regulated in response to selenite stress. Overexpression of ERF96 enhanced Arabidopsis resistance to selenite stress, while ERF96-silenced plants demonstrated wild-type (WT) resistance to selenite. In addition, the overexpression plants had significantly lower selenium (Se) content in shoots when subjected to selenite stress. Further investigation indicated that overexpression of ERF96 reduced transcript levels of selenite/phosphate transporters PHT1;1 and PHT2;1, which influenced Arabidopsis Se uptake and allocation in the presence of selenite. Moreover, our experiments showed that overexpression of ERF96 enhanced Arabidopsis antioxidant activity. Under selenite stress, ERF96-overexpressing lines exhibited the significant increases in catalase (CAT) and glutathione peroxidase (GPX) activities as well as the glutathione (GSH) content, while had a decrease in reactive oxygen species (ROS) accumulation compared to WT. Taken together, our results demonstrate that ERF96 plays a positive role in the regulation of selenite tolerance in Arabidopsis.

The role of cytokinin in selenium stress response in Arabidopsis.

Cytokinins (CKs) regulate many developmental processes and environmental stress responses in plants. In this study, our data provide evidence that CK negatively regulates Arabidopsis selenium (Se) stress response. CK-deficient plant ipt1 3 5 7 exhibited enhanced Se tolerance which was abolished by exogenous benzylaminopurine (BA) application, while CK- receptor -deficient mutants ahk2 and ahk3 were sensitive to Se stress. Further investigation suggested that CK regulated Se tolerance of ipt1 3 5 7 through reduction of Se uptake and activation of metabolism detoxification, which had significantly lower transcriptions of high-affinity transporters PHT1;1, PHT1;8, PHT1;9 and the higher transcription of selenocysteine methyltransferase (SMT) respectively. Moreover, Se tolerance of ipt1 3 5 7 was associated with the enhanced antioxidant levels which had the higher catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX) activities as well as the higher glutathione (GSH) content. On the other hand, loss-of-function mutations in single CK receptor genes could increase Se uptake and reactive oxygen species (ROS) accumulation, which caused Se sensitivity in ahk2 and ahk3 mutants. Taken together, these findings provide new insights to the role of CK in Se stress response in Arabidopsis.

Cytokinin is involved in TPS22-mediated selenium tolerance in Arabidopsis thaliana.

Background and Aims: Excess selenium (Se) is toxic to plants, but relatively little is known about the regulatory mechanism of plant Se tolerance. This study explored the role of the TPS22 gene in Se tolerance in Arabidopsis thaliana. Methods: Arabidopsis wild type and XVE mutant seeds were grown on half-strength MS media containing Na2SeO3 for screening of the Se-tolerant mutant tps22. The XVE T-DNA-tagged genomic sequence in tps22 was identified by TAIL-PCR. The TPS22 gene was transformed into the mutant tps22 and wild type plants using the flower infiltration method. Wild type, tps22 mutant and transgenic seedlings were cultivated on vertical plates for phenotype analysis, physiological index measurement and gene expression analysis. Key Results: We identified an Arabidopsis Se-tolerant mutant tps22 from the XVE pool lines, and cloned the gene which encodes the terpenoid synthase (TPS22). TPS22 was downregulated by Se stress, and loss-of-function of TPS22 resulted in decreased Se accumulation and enhanced Se tolerance; by contrast, overexpression of TPS22 showed similar traits to the wild type under Se stress. Further analysis revealed that TPS22 mediated Se tolerance through reduction of Se uptake and activation of metabolism detoxification, which decreased transcription of high-affinity transporters PHT1;1, PHT1;8 and PHT1;9 and significantly increased transcription of selenocysteine methyltransferase (SMT), respectively. Moreover, loss-of-function of TPS22 resulted in reduced cytokinin level and repression of cytokinin signalling components AHK3 and AHK4, and upregulation of ARR3, ARR15 and ARR16. Exogenous cytokinin increased transcription of PHT1;1, PHT2;1 and SMT and decreased Se tolerance of the tps22 mutant. In addition, enhanced Se resistance of the tps22 mutant was associated with glutathione (GSH). Conclusions: Se stress downregulated TPS22, which reduced endogenous cytokinin level, and then affected the key factors of Se uptake and metabolism detoxification. This cascade of events resulted in reduced Se accumulation and enhanced Se tolerance.