Sucrose-specific signalling represses translation of the Arabidopsis ATB2 bZIP transcription factor gene.

The Arabidopsis bZIP transcription factor gene ATB2 has been shown previously to be expressed in a light-regulated and tissue-specific way. Here we describe the precise localization of ATB2 expression, using transgenic lines containing an ATB2 promoter-GUS reporter gene construct. The observed expression pattern suggests a role for ATB2 in the control of processes associated with the transport or utilization of metabolites. Remarkably, expression of the ATB2-GUS reporter gene construct was specifically repressed by sucrose. Other sugars, such as glucose and fructose, alone or in combination, were ineffective. Repression was observed at external sucrose concentrations exceeding 25 mM. Transcript levels of both the endogenous ATB2 gene and the ATB2-GUS reporter gene were not repressed by sucrose, suggesting that sucrose affects mRNA translation. This translational regulation involves the ATB2 leader sequence because deletion of the leader resulted in loss of sucrose repression. Our results provide evidence for a sucrose-specific sugar sensing and signalling system in plants.