Transcriptional regulation of an ADP-glucose pyrophosphorylase small subunit expression in Solanum tuberosum L.
1996
Harvengt, L.
A genomic clone encoding a small subunit of ADP-glucose pyrophosphorylase (AGPase) was isolated front potato cv Desire. The proximal part of the promoter includes an AT-rich region and two types of repetition, one of them comprising a class I patatin cis-acting element involved in tuber-specific expression and inducibility by sucrose in that gene. Evidences for the occurrence of at least another small subunit gene are discussed. The promoter of the studied gene (named AgpB1) directs strong expression of the GUS reporter gene in developing tubers and in the adjacent stolons. In other organs, activity is restricted to stomata guard cells, pollen, placenta and to the perivascular starch sheath as well as (at a lower level) to the phloemian parenchymas. Hence, this pattern is very similar to that found for the AGPS gene coding for a large subunit of AGPase. The regulation of promoter ativity in response to externally added hormones and metabolites was investigated. A deletion analysis made possible a first assignment of function to the different parts of the promoter. The longest fragment directed gusA expression in strong parallelism with AGPase activity and starch content throughout the tomato fruit development. It thus seems that, in potato, modulation of the AGPase properties according to the cellular context could be, at least in part, achieved by differential expression of genes within both the large and small subunit gene families. Many analogies with storage proteins were enlighted at both the expression pattern and promoter sequence levels. The described promoter will be available for targeted expression of transgenes. It will be a valuable tool for investigating the effective physiological function of the perivascular starch sheath and in elucidating further the molecular basis of tuberisation.
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