Isolation and characterization of cDNAs encoding mitochondrial phosphate transporters in soybean, maize, rice, and Arabidopsis

cDNA clones encoding mitochondrial phosphate transporters were isolated fro m four herbaceous plants. The cDNAs for the soybean, maize and rice transpo rters contained entire coding regions, whereas the Arabidopsis cDNA lacked the 5' portion. The hydropathy profiles of the deduced amino acid sequences predicted the existence of six membrane-spanning domains which are highly conserved in the mitochondrial transporter family. In soybeans, the mRNA le vel for the transporter was high in tissues containing dividing cells. It w as suggested that there are multiple copies of transporter genes in both di cots and monocots. The soybean transporter was expressed as inclusion bodie s in Escherichia coli, solubilized with detergents, and then reconstituted into liposomes. The resulting proteoliposomes exhibited high phosphate tran sport activity. The activity was inhibited by N-ethylmaleimide, like those of mammalian phosphate transporters.