A conserved uORF mediates sucrose-induced repression of translation

Sugars as signalling molecules regulate the expression of numerous plant genes. Most genes are controlled via transcriptional regulation but other mechanisms have been uncovered as well. These include the control of mRNA stability and translation, and protein stability. A sucrose specific translation control mechanism was recently discovered, which controls translation of the group S bZIP-type transcription factor ATB2/AtbZIP1.1 This control requires the very long 5’UTR of the gene. The elements involved in translational control were identified by studying point mutations and deletions in the 5’UTR. A highly conserved uORF that encodes 42 amino acids is required for sucrose repression. This uORF is conserved in 5’UTRs of bZIP-transcription factors from four other Arabidopsis genes and many other plant species. The AtbZIP11 gene shows a restricted expression patterns and seems mainly associated with vascular tissues. However, the sucrose repression system is operating throughout the plant as shown by ectopic expression of a 5’UTR construct using the ubiquitin 10 promoter. The other Arabidopsis conserved uORF encoding transcription factors (AtbZIP1, 2, 44, 53) show similar sucrose-induced repression of translation. A general sucrose specific translational mechanism is suggested, dependent on the presence of the conserved uORF. The target genes of these transcription factors are most likely regulated in a sucrose-dependent way. Such target genes are currently being identified using the novel DamID system, which uses directed methylation of promoter regions.