Background: Metal selectivity is an important feature of the plant cation diffusion facilitator (CDF) transporter family. Results: Mutation of key residues can narrow or broaden metal selectivity. Conclusion: Residues within the cytoplasmic histidine-rich loop and transmembrane domains define metal specificity. Significance: This raises the possibility of engineering transporters for selective biofortification of cereal grains with nutritionally essential metals.
Zinc plays many essential roles in life. As a strong Lewis acid that lacks redox activity under environmental and cellular conditions, the Zn 2+ cation is central in determining protein structure and catalytic function of nearly 10% of most eukaryotic proteomes. While specific functions of zinc have been elucidated at a molecular level in a number of plant proteins, wider issues abound with respect to the acquisition and distribution of zinc by plants. An important challenge is to understand how plants balance between Zn supply in soil and their own nutritional requirement for zinc, particularly where edaphic factors lead to a lack of bioavailable zinc or, conversely, an excess of zinc that bears a major risk of phytotoxicity. Plants are the ultimate source of zinc in the human diet, and human Zn deficiency accounts for over 400 000 deaths annually. Here, we review the current understanding of zinc homeostasis in plants from the molecular and physiological perspectives. We provide an overview of approaches pursued so far in Zn biofortification of crops. Finally, we outline a ''push-pull'' model of zinc nutrition in plants as a simplifying concept. In summary, this review discusses avenues that can potentially deliver wider benefits for both plant and human Zn nutrition.
Aim: We investigated the phylogeographical history of a clonal-sexual orchid, to test the hypothesis that current patterns of genetic diversity and differentiation retain the traces of climatic fluctuations and of the species reproductive system.
Location: Europe, Siberia and Russian Far East.Taxon: Cypripedium calceolus L. (Orchidaceae).Methods: Samples (>900, from 56 locations) were genotyped at 11 nuclear microsatellite loci and plastid sequences were obtained for a subset of them. Analysis of genetic structure and approximate Bayesian computations were performed.Species distribution modelling was used to explore the effects of past climatic fluctuations on the species range. Results: Analysis of genetic diversity reveals high heterozygosity and allele diversity, with no geographical trend. Three genetic clusters are identified with extant gene pools derived from ancestral demes in glacial refugia. Siberian populations exhibit different plastid haplotypes, supporting an early divergence for the Asian gene pool. Demographic results based on genetic data are compatible with an admixture event explaining differentiation in Estonia and Romania and they are consistent with past climatic dynamics inferred through species distribution modelling. Current population differentiation does not follow isolation by distance model and is compatible with a model of isolation by colonization. Main conclusions: The genetic differentiation observed today in C. calceolus preserves the signature of climatic fluctuations in the historical distribution range of the species. Our findings support the central role of clonal reproduction in the reducing loss of diversity through genetic drift. The dynamics of the clonal-sexual reproduction are responsible for the persistence of ancestral variation and stability during glacial periods and post-glacial expansion.
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