Romanian Biotechnological Letters Vol. 15, No.2, Supplement, 2010 Copyright © 2010 University of Bucharest Printed in Romania. All rights reserved SHORT COMUNICATION 117 Biofortification of barley grains by cell-type-specific expression of a vacuolar metal transporter Received for publication, January 21, 2009 Accepted, February 2, 2010 DORINA PODAR 1,2 , DALE SANDERS 2 1 Faculty of Biology-Geology, Babes-Bolyai University, 1 Kogalniceanu St., Cluj-Napoca, 400084, Clluj, Romania; tel/fax: +40264570388, e-mail corresponding author: dorina.podar@gmail.com , 2 Department of Biology, University of York, Heslington, YO10 5DD, York, UK. Abstact Transition metals are universally present in our environment occurring either naturally or resulting from anthropogenic activities. Many of the transition metals (e.g. Fe, Zn, Cu, Mn, Ni, Co) are essential for all forms of life, playing important roles as cofactors of numerous enzymes, in stabilising transcription factors and in regulatory and structural proteins. However, when present at high concentrations these metals become toxic alongside with other metals (e.g. Cd, Pb) that have no known biological function. The only source of metals for humans is through diet and ultimately the source of mineral elements is therefore plant tissues. Consequently, the presence of minerals and the maintenance of their homeostasis within the edible tissues of plants are of great importance for human nutrition. One of the essential elements for both plants and humans is Zn. Zinc is a trace element, essential in sustaining all biological organisms and is present in all enzyme classes – oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases (Broadley et al., 2007). Over 3200 putative zinc-binding proteins have been estimated within the human proteome (Andreini et al., 2006) i.e. more than 10% percent of proteins encoded by the genome. The WHO places Zn and Fe among the micronutrients - alongside Vitamin A – for which deficit is most acute in the human diet and for which enhancement is necessary. To a large degree, these deficiencies worldwide arise from the low content of Fe and Zn in polished grains and from the tendency of other components in predominantly vegetable diets to chelate the already-low concentrations of these essential metals. Recently, biofortification has been proposed as a complementary solution to address human mineral malnutrition. Biofortification has been defined as the process of increasing the bioavailable concentrations of essential elements in the edible portions of crop plants through agronomic intervention or genetic selection. I order to address biofortification of grains with mineral elements, the transporters involved in the deposition of these elements in grains and their metal specificity has to be identified. A recent barley grain microarray, consisting of cDNA clones of relevance for heavy metal transport and deposition, suggested that Metal Tolerance Proteins (MTPs) might be involved in the deposition of Zn in the endosperm during grain filling (Tauris et al., 2009). MTPs are plant members of the large Cation Diffusion Facilitator (CDF) family of transporters. CDFs are ubiquitous to all form of life (Archaea, Bacteria and Eukaryotes), more than 400 members being reported so far. CDFs are all localized either at the plasma membrane, vacuolar membrane (in plants), vesicles or at the endocompartments and are involved in maintaining the cellular metal homeostasis by catalyzing the efflux of transition metal cations from the cytoplasm to the outside of the cell or into subcellular compartments. Functional aspects of CDFs have been little investigated within plants and not at all in cereals. In barley, likewise in rice, HvMTP1 appears to be the major representative of the Zn- group of CDF transporters and it is expressed ubiquitously in root, shoot and grain tissues