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Key message: CIPAS8 is a novel Cd-influx and Co-efflux transporters, and Ser86 and Cys128 might play a decisive role in Co-binding and translocation. Cadmium (Cd) is among the most toxic heavy metals and is a widespread environmental pollutant. Cobalt (Co) is a mineral nutrient that is essential for plant growth and development, but high concentrations may be toxic. Cadmium-induced protein AS8 (CIPAS8) is widely distributed among plant species and might be induced by heavy metals, but its function has not been studied previously. In this study, Populus euphratica PeCIPAS8 and Salix linearistipularis SlCIPAS8 were investigated. The transcription of both genes was significantly enhanced under Cd and Co stresses. PeCIPAS8 and SlCIPAS8 conferred sensitivity to Cd in transgenic yeast, allowing higher quantities of Cd to accumulate within the cells, whereas SlCIPAS8 also conferred tolerance to Co and reduced Co accumulation. The determinants of substrate selectivity of the SlCIPAS8 protein were examined by site mutagenesis, which indicated that the Ser at 86th (S86) substituted for Arg (R) [S86R] and Cys at 128th (C128) substituted for Ser [C128S] mutations limited the protein's capability for Co translocation. These results suggested that PeCIPAS8 and SlCIPAS8 may be involved in Cd uptake into the plant cell. SlCIPAS8 can reduce excess Co accumulation to maintain intracellular Co homeostasis, and the site mutations S86R and C128S were essential for Co transport. These findings provide insight into the function of CIPAS8 and highlight its potential for utilization in phytoremediation applications. [ABSTRACT FROM AUTHOR]

Key message: TuCAX1a and TuCAX1b improved Ca2+ and Zn2+ translocation and TuCAX1b enhanced Ca2+, Zn2+, Mn2+ and Fe2+ content when exposed to Cd2+; Cd2+ translocation was inhibited under Ca2+ and Zn2+. Cation/H+ antiporters (CAXs) are involved in the translocation of Ca2+ and various metal ions in higher plants. In the present study, TuCAX1a and TuCAX1b, two cation/H+ antiporters, were isolated from the diploid wheat Triticum urartu, and their metal cation translocation functions investigated. TuCAX1a and TuCAX1b showed abundant tissue-specific expression in the internode and beard, respectively, and their expression levels were increased in shoots exposed to Cd2+, Zn2+ and Ca2+. Plant phenotype analysis showed that overexpression of TuCAX1a and TuCAX1b could improve the tolerance of Arabidopsis to exogenous Ca2+ and Zn2+. In the plant shoots and roots, the contents of Ca2+ and Zn2+ were higher than wild-type plants under Ca2+ and Zn2+ treatments, indicating that TuCAX1a and TuCAX1b can enhance Ca2+ and Zn2+ translocation. Ca2+, Zn2+, Mn2+ and Fe2+ contents showed higher accumulation in TuCAX1b-transgenic Arabidopsis shoots than in wild-type plants exposed to Cd2+, and the translocation of Cd2+ was inhibited under Ca2+ and Zn2+. Overall, the present study provides a novel genetic resource for improving the uptake of microelements and reducing accumulation of toxic heavy metals in wheat. [ABSTRACT FROM AUTHOR]

Key message: Cysteine in the N-terminal metal-binding domain (N-MBD) of TaHMA2 participates in Zn2+/Cd2+ binding and translocation in Arabidopsis.Abstract: Wheat heavy metal ATPase 2 (TaHMA2) can transport Zn2+ and Cd2+ across membranes. A previous study showed that cysteine (Cys) and glutamate residues in the N-terminal metal-binding domain (N-MBD) were necessary for metal-binding and translocation of TaHMA2 in yeast. However, the function of TaHMA2 in plants was not fully revealed. In this study, we investigated the roles of the CCxxE and CPC motifs in the N-MBD and the N/C-terminal regions of TaHMA2 in Zn2+/Cd2+ translocation in root and shoot of Arabidopsis. Compared with the wild type, overexpression of TaHMA2 and the TaHMA2 derivative (glutamic substituted for alanine from CCxxE) in Arabidopsis increased root length, fresh weight and enhanced Zn2+/Cd2+ root-to-shoot translocation. The plants with a truncated N/C-terminal of TaHMA2 were impaired in Zn2+/Cd2+ tolerance and translocation, while mutagenesis of Cys in the N-MBD reduced the tolerance and transport activity of TaHMA2, suggesting the involvement of Cys in Zn2+/Cd2+ binding and translocation in Arabidopsis. This study therefore provides a theoretical possibility for the application of TaHMA2 in transgenic breeding to regulate metal element balance in crop plants. [ABSTRACT FROM AUTHOR]

Some heavy metal-tolerant bacteria recognized as plant growth-promoting bacteria (PGPB) could improve plant growth. Here, the growth and Cd accumulation of Solanum nigrum seedling inoculated by soaking the roots in a dilute suspension of the Cd-tolerant strains ZGKD5 or ZGKD2 were investigated. The results showed that both ZGKD5 and ZGKD2 exhibited the characterization of producing IAA, siderophores, ammonia, and biosurfactant, and solubilizing phosphate and fixing nitrogen. The siderophores produced by both strains could chelate various heavy metals, such as Cu, Cd, Zn, and Ni. The shoot height, root length, number of fibrous root, and dry weight of S. nigrum seedling were significantly increased by inoculation with ZGKD5 or ZGKD2 in the absence or presence of Cd stress. The Cd concentration and translocation from root to shoot in seedlings were remarkably increased, indicating that both strains could improve the growth and Cd phytoextraction of S. nigrum. The activities of SOD, POD, CAT, and APX in both inoculated and uninoculated plants were increased under Cd stress, indicating that these antioxidative enzymes could alleviate oxidative stress induced by Cd. Furthermore, activities of antioxidative enzyme in inoculated plants exposed to Cd stress was lower than that in uninoculated Cd-stressed plants, which might be due to the decreasing metabolism caused by high levels of Cd. These results indicated that strains ZGKD5 and ZGKD2 are PGPB and have the potential for improving the phytoremediation of S. nigrum in Cd-contaminated farmland soil. [ABSTRACT FROM AUTHOR]

Background: HMA4 transporters are involved in the transport and binding of divalent heavy metals (Cd, Zn, Pb [lead] and Co [cobalt]). In general, as efflux pumps, HMA4 transporters can increase the heavy metal tolerance of yeast and Escherichia coli. Additional research has shown that the C-terminus of HMA4 contains a heavy metal-binding domain and that heterologous expression of a portion of peptides from this C-terminal domain in yeast provides a high level of Cd tolerance and Cd hyperaccumulation. Results: We cloned BjHMA4 from Brassica juncea, and quantitative real-time PCR analysis revealed that BjHMA4 was upregulated by Zn and Cd in the roots, stems and leaves. Overexpression of BjHMA4 dramatically affects Zn/Cd distribution in rice and wheat seedlings. Interestingly, BjHMA4 contains a repeat region named BjHMA4R within the C-terminal region; this repeat region is not far from the last transmembrane domain. We further characterized the detailed function of BjHMA4R via yeast and E. coli experiments. Notably, BjHMA4R greatly and specifically improved Cd tolerance, and BjHMA4R transformants both grew on solid media that contained 500 μM CdCl2 and presented improved Cd accumulation (approximately twice that of wild-type [WT] strains). Additionally, visualization via fluorescence microscopy indicated that BjHMA4R clearly localizes in the cytosol of yeast. Overall, these findings suggest that BjHMA4R specifically improves Cd tolerance and Cd accumulation in yeast by specifically binding Cd2+ in the cytosol under low heavy metal concentrations. Moreover, similar results in E. coli experiments corroborate this postulation. Conclusion: BjHMA4R can specifically bind Cd2+ in the cytosol, thereby substantially and specifically improving Cd tolerance and accumulation under low heavy metal concentrations. [ABSTRACT FROM AUTHOR]

Toxic heavy metals originating from human activities have caused irreversible harm to the environment. Toxic heavy metal ions absorbed by crop plants can seriously threaten human health. Therefore, decreasing heavy metal contents in crop plants is an urgent need. The plant cadmium resistance protein (PCR) is a heavy metal ion transporter. In this study, PePCR10 was cloned from Populus euphratica. Bioinformatics analyses revealed its transmembrane structure and gene sequence motifs. The transcript profile of PePCR10 was analyzed by RT-qPCR, and its transcript levels increased under toxic heavy metal (cadmium, lead, aluminum) treatments. Subcellular localization analyses in tobacco cells revealed that PePCR10 localizes at the plasma membrane. Compared with wild type (WT), PePCR10 -overexpressing lines showed significantly higher values for plant height, root length, fresh weight, and dry weight under heavy metal stress. Electrolyte leakage, nitroblue tetrazolium staining, and chlorophyll fluorescence analyses indicated that Cd/Al tolerance in PePCR10 -overexpressing lines was stronger than that in WT. The Cd/Al contents were lower in the PePCR10 -overexpressing lines than in WT under Cd/Al stress. Our results show that PePCR10 can reduce the heavy metal content in poplar and enhance its Cd/Al tolerance. Hence, PePCR10 is a candidate genetic resource for effectively reducing heavy metal accumulation in crops. [Display omitted] • PePCR10 was confirmed to be a plasma membrane-localized protein. • PePCR10 enhanced Cd/Al tolerance by promoting Cd/Al efflux in poplar. • PePCR10 can be used to reduce the risks of heavy metals to humans. [ABSTRACT FROM AUTHOR]

• Node Ⅰ plays critical role in metal transportation. • OsLCT1, OsHMA2 and OsZIP3 are involved in cadmium and zinc distribution. • Transgene-Stacking II system helps to co-express three transporters efficiently. • Co-expression rice lines are low Cd accumulation plants. The OsHMA2, OsLCT1 and OsZIP3 transporters were all involved in zinc (Zn) and cadmium (Cd) transport. So far, only a few researches studied on the co- regulation effect of three transporters related to Zn and Cd transport. The present study showed that rice co- expressing OsLCT1 - OsHMA2 - OsZIP3 (LHZ) had longer roots and shoots than wild-type (WT) rice after Zn and Cd treatments. The chlorophyll content was significantly higher, and the proline, malondialdehyde and H 2 O 2 contents were significantly lower in co- transgenic lines than in WT under Cd and Zn stress. LHZ in the seedlings of transgenic rice decreased the root-to-shoot translocation of Cd after Cd and Zn treatments. At the filling stage, LHZ line reduced Cd accumulation in grain after Cd treatment. Moreover, LHZ line increased the translocation of Zn to grain and reduced the accumulation of Cd after Zn treatment. These results suggested that LHZ co-expression could effectively decrease the translocation and accumulation of Cd to grains, alleviated the oxidative stress of Cd and Zn, and finally enhanced the quality and safety of rice grains. [ABSTRACT FROM AUTHOR]