Abstract
The presence of the toxic metal cadmium (Cd2+) in certain foodstuffs is recognised as a global problem, and there is increasing legislative pressure to reduce the content of Cd in food. The present study was conducted on cacao (Theobroma cacao), the source of chocolate, and one of the crops known to accumulate Cd in certain conditions. There are a range of possible genetic and agronomic methods being tested as a route to such reduction. As part of a gene-based approach, we focused on the Natural Resistance-Associated Macrophage Proteins (NRAMPS), a family of proton/metal transporter proteins that are evolutionarily conserved across all species from bacteria to humans. The plant NRAMP gene family are of particular importance as they are responsible for uptake of the nutritionally vital divalent cations Fe2+, Mn2+, Zn2+, as well as Cd2+. We identified the five NRAMP genes in cacao, sequenced these genes and studied their expression in various organs. We then confirmed the expression patterns in response to variation in nutrient cation availability and addition of Cd2+. Functional analysis by expression in yeast provided evidence that NRAMP5 encoded a protein capable of Cd2+ transport, and suggested this gene as a target for genetic selection/modification.
Highlights
Natural Resistance-Associated Macrophage Proteins (NRAMPS) represent a family of proton/metal transporter proteins that are evolutionarily conserved across all species from bacteria to humans[1,2]
Six Natural resistance-associated macrophage proteins (NRAMPs) homologs were identified for the ancient vascular plant species Selaginella moellendorffii compared to three homologs in the basal angiosperm Amborella trichopoda
The members of NRAMP family have been identified and functionally characterized in number of plant species including Arabidopsis, rice, and soybean[8,9,10,11,12], to date such information is lacking in cacao
Summary
Natural Resistance-Associated Macrophage Proteins (NRAMPS) represent a family of proton/metal transporter proteins that are evolutionarily conserved across all species from bacteria to humans[1,2]. In an attempt to reduce the levels of Cd2+ in crops, including cacao (the source of chocolate), a variety of research studies are underway to develop agronomic[3,4] or genetic[5] solutions to this problem. This present study focused on the characterization of the NRAMP gene family in cacao and was designed to investigate the possible role of these proteins in controlling levels of Cd2+ in this crop. It is hoped that such investigations will inform genetic approaches to selecting cacao clones with reduced Cd2+ or using gene-editing methods to modify existing clones
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