The regulation of assimilate allocation and transport

In higher plants, sugars possess multiple functions: transport and storage of carbon and energy as well as signal molecules. A variety of sugar transporters have been cloned that show differential expression between source and sink tissues. Expression of these transporters is highly regulated, according to the local metabolic status and the demands of long distance transport. Very little knowledge is available on mechanisms underlying the regulation of sugar transporter expression in plants. Studies in E. coli, yeast and mammals have unravelled complex regulatory pathways with crosstalk between sugar transport and metabolism. Recent studies in plants provide increasing evidence for the existence of similar regulatory mechanisms. In many cases, connections have been found between C- and N-metabolism, implicating a tight network of signal transduction and metabolism. Some aspects of this network are presented in this review, emphasising sugar transport and sugar signal transduction.