Sucrose signaling in higher plants

Sucrose controls various developmental and metabolic processes in plants. In this review, we evaluate whether sucrose could be a preferred signaling molecule that controls processes like carbohydrate metabolism, accumulation of storage proteins, sucrose transport, anthocyanin accumulation, and floral induction. We summarize putative sucrose-dependent signaling pathways. Sucrose, but not other sugars, stimulates the genes that encode ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase I, and UDP-glucose pyrophosphorylase in several species. The class-1 patatin promoter is induced under high sucrose conditions in potato (Solanum tuberosum). Exogenous sucrose reduces the loading of sucrose to the phloem by inhibiting the expression of the sucrose transporter and its protein activity in sugar beet (Beta vulgaris). Sucrose also influences a wide range of growth processes, including cell division, ribosome synthesis, cotyledon development, far-red light signaling, and tuber development. Floral induction is promoted by sucrose in several species. The molecular mechanisms by which sucrose functions as a signal are largely unknown. Sucrose enhances the expression of transcription factors such as AtWRKY20 and MYB75, which function upstream of the sucrose-responsive genes. Sucrose controls the expression of AtbZIP11 at the post-transcriptional level by the peptide encoded by uORF2. Sucrose levels affect translation of a group of mRNAs in Arabidopsis. Sucrose increases the activity of AGPase by posttranslational redox-modification. Sucrose interrupts the interaction between sucrose transporter SUT4 and cytochrome b5. In addition, the SNF-related protein kinase-1 appears to be involved in sucrose-dependent pathways by controlling sucrose synthase (SUS4) expression.