PLANT MEMBERS OF A FAMILY OF SULFATE TRANSPORTERS REVEAL FUNCTIONAL SUBTYPES

Three plant sulfate transporter cDNAs have been isolated by complement ation of a yeast mutant with a cDNA library derived from the tropical forage legume Stylosanthes hamata. Two of these cDNAs, shst1 and shst2 , encode high-affinity H+/sulfate cotransporters that mediate the upta ke of sulfate by plant roots from low concentrations of sulfate in the soil solution, The third, shst3, represents a different subtype encod ing a lower affinity H+/sulfate cotransporter, which may be involved i n the internal transport of sulfate between cellular or subcellular co mpartments within the plant. The steady-state level of mRNA correspond ing to both subtypes is subject to regulation by signals that ultimate ly respond to the external sulfate supply. These cDNAs represent the i dentification of plant members of a family of related sulfate transpor ter proteins whose sequences exhibit significant amino acid conservati on in filamentous fungi, yeast, plants, and mammals.