Molecular mechanisms of phosphate and sulphate transport in plants

The application of molecular techniques in recent years has advanced our understanding of phosphate and sulphate transport processes in plants. Genes encoding phosphate and sulphate transporters have been isolated from a number of plant species. The transporters encoded by these genes are related to the major facilitator superfamily of proteins. They are predicted to contain 12 membrane-spanning domains and function as H+/ or H+/ cotransporters. Both high-affinity and low-affinity types have been identified. Most research has concentrated on genes that encode transporters expressed in roots. The expression of many of these genes is transcriptionally regulated by signals that respond to the nutrient status of the plant. Nutrient demand and the availability of precursors needed in the assimilatory pathways also regulate transcription of some of these genes. Information on the cell types in which phosphate and sulphate transporters are expressed is becoming available. These data, together with functional characterisation of the transporters, are enabling the roles of various transporters in the overall phosphate and sulphate nutrition of plants to be defined.