title: Cytotoxic thio-malate is transported by both an aluminum-responsive malate efflux pathway in wheat and the MAE1 malate permease in Schizosaccharomyces pombe.
abstract: Aluminum (Al) tolerance in wheat (Triticum aestivum L.) is mainly achieved by malate efflux, which is regulated by the expression of the recently identified gene, presumably encoding an Al-activated malate efflux transporter (ALMT1). However, the transport mechanism is not fully understood, partly as a result of the rapid turnover of its substrate. We developed a tool to study malate transport in wheat by screening biological compounds using the well-characterized Schizosaccharomyces pombe malate transporter (SpMAE1). Expression of SpMAE1 in both S. pombe and Saccharomyces cerevisiae, which has no SpMAE1 homologue, caused hypersensitivity to thio-malic acid. This hypersensitivity was prominent at pH 3.5, but not pH 4.5, and was accompanied by an increase in thiol content, indicating that SpMAE1 mediates the uptake of thio-malic acid at a specific low pH. In wheat, root apices were able to accumulate thio-malic acid without growth reduction at pH values above 4.2. Pretreatment of root apices with thio-malic acid followed by Al treatment induced thio-malate efflux. Al-induced thio-malate efflux was much higher in Al-resistant cultivars/genotypes than in Al-sensitive ones, and was accompanied by a decrease in thiol-content. Thio-malate efflux in the Al-resistant cultivar was slightly activated by lanthanum or ytterbium ion. Thio-malic acid did not alleviate the Al-induced inhibition of root elongation in wheat. Taken together, our results suggest that thio-malate acts as an analogue for malate in malate transport systems in wheat and yeast, and that it may be a useful tool for the analysis of malate transport involved in Al-tolerance and of other organic ion transport processes.
authors.affiliation: Research Institute for Bioresources, Okayama University, 2-20-1 Chuo, Kurashiki, 710-0046 Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Osawa
authors.forename: Hideaki
authors.initials: H
authors.lastname: Matsumoto
mesh_terms: D000535:Aluminum / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D016923:Cell Death; D005816:Genetic Complementation Test; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D027361:Organic Anion Transporters / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000166:cytology; D012568:Schizosaccharomyces / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D013870:Thiomalates / Q000737:chemistry / Q000378:metabolism*; D014908:Triticum / Q000187:drug effects / Q000378:metabolism*
chemical_list: C513834:MAE1 protein, S pombe; D027361:Organic Anion Transporters; D029702:Schizosaccharomyces pombe Proteins; D013870:Thiomalates; D000535:Aluminum