Separate cis sequences and trans factors direct metabolic and developmental regulation of a potato tuber storage protein gene

Summary The expression of genes encoding patatin, a major tuber protein, is highly tissue‐specific but is also modulated by exogenous sucrose. The patterns of transcription observed in potato plants could be due to mechanisms conferring tuber‐specificity or they could reflect the concentrations of sucrose found in different tissues. To distinguish between these possibilities, a detailed examination was made of the function of a region of the promoter previously implicated in conferring tissue‐specific and sucrose‐inducible expression. Internal deletions of this region revealed three separate functional domains regulating expression. The B repeat region acted as a positive activator of transcription in the tuber and was also responsible for a degree of sucrose‐inducibility. The distal region of the A repeat repressed transcription in leaf and tuber tissue, while the proximal region of the A repeat was able to confer sucrose‐responsiveness. Each of these regions specifically bound nuclear proteins which may be putative transcription factors involved in conferring these responses. The region found to confer sucrose‐inducible expression was conserved among some other genes that are also regulated by exogenous sucrose.