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.

A role for APX1 gene in lead tolerance in Arabidopsis thaliana.

Lead (Pb) is a dangerous and widespread metal pollutant. Numerous studies have been made in understanding heavy metal detoxification and tolerance in plants, however, relatively few are known about the mechanisms involved in Pb stress response. In this study, we provide evidence for a novel role of APX1 gene in Pb tolerance in Arabidopsis. KO-APX1 mutants apx1-3 and apx1-4 showed more resistant than wild type, and the APX1-complementary COM1 restored the growth state of wild type in Pb stress. The two KO-APX1 mutants showed reduced Pb accumulation, which was accompanied by the activation of metal transporters PDR12 and ATM3 genes expression. In addition, glutathione (GSH), phytochelatin (PC) synthesis and related gene GSH1, GSH2, PCS1 and PCS2 expression were also increased in apx1-3 plants subjected to Pb stress. The more improvements in antioxidant enzymes glutathione peroxidase (GPX) and catalase (CAT) activities were found in the mutant apx1-3. Taken together, our results suggest that APX1 gene knockout results in enhanced Pb tolerance mainly through activating the expression of the ATP-bind cassette (ABC)-type transporters and at least partially through GSH -dependent PC synthesis pathway by coordinated control of gene expression.

Loss-of-function mutations in the APX1 gene result in enhanced selenium tolerance in Arabidopsis thaliana.

It is generally recognized that excess selenium (Se) has a negative effect on the growth and development of plants. Numerous studies have identified key genes involved in selenium tolerance in plants; however, our understanding of its molecular mechanisms is far from complete. In this study, we isolated an Arabidopsis selenium-resistant mutant from the mutant XVE pool lines because of its increased root growth and fresh weight in Se stress, and cloned the gene, which encodes the cytosolic ascorbate peroxidase (APX1). Two other APX1 gene knockout allelic lines were also selenium resistant, and the APX1-complementary COM1 restored the growth state of wild type under Se stress. In addition, these APX1 allelic lines accumulated more Se than did wild-type plants when subjected to Se stress. Further analysis revealed that the APX1-mediated Se tolerance was associated, at least in part, with the enhanced activities of antioxidant enzymes catalase, glutathione peroxidase and glutathione reductase. Moreover, enhanced Se resistance of the mutants was associated with glutathione (GSH), which had the higher expression level of GSH1 gene involved in GSH synthesis and consequently increased GSH content. Our results provide genetic evidence indicating that loss-of-function of APX1 results in tolerance to Se stress.