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 transp orters have been cloned that show differential expression between source an d sink tissues. Expression of these transporters is highly regulated, accor ding to the local metabolic status and the demands of long distance transpo rt. Very little knowledge is available on mechanisms underlying the regulat ion of sugar transporter expression in plants. Studies in E. coli, yeast an d mammals have unravelled complex regulatory pathways with crosstalk betwee n sugar transport and metabolism. Recent studies in plants provide increasi ng evidence for the existence of similar regulatory mechanisms. In many cas es, connections have been found between C- and N-metabolism, implicating a tight network of signal transduction and metabolism. Some aspects of this n etwork are presented in this review, emphasising sugar transport and sugar signal transduction.