The potato glucosyltransferase gene promoter is environmentally regulated

Anthocyanidine glucosyltransferase (GT) is a key upregulating enzyme in anthocyanins stability. A 1.6 kb-GT promoter from Solanum sogarandinum has been isolated and its sequence analysed. The inspection of the promoter sequence revealed several boxes important for the regulation of gene expression. The motifs arrangement was studied using transgenic potato plants transformed with a GT promoter-β-glucuronidase gene fusion construct. The exposure of the transgenic potato to UV, cold, light, as well as the salt and ABA treatment resulted in 5.5-, 6-, 5-, 5- and 8-fold increase in enzyme activity, respectively. The synergistic mode of cold-light and ABA-cold effect has been detected. The UV and cold inducibility of promoter implicates its upregulatory function in flavonoid stability and thus the regulatory role in plant protection against abiotic stresses. In turn, the increase in sucrose concentration (over 2%) in growth medium inhibits GT promoter driven GUS activity. The changes in GT promoter activity upon treatment was confirmed in most cases by western analysis of unmodified plant treated in the same way. The only difference was NaCl treatment that resulted in unchanged GT protein level. Histochemical analysis of GUS under GT promoter revealed the cell specific expression. In leaves the highest expression has been detected in epidermis and spongy mesophyll, but weak staining signals were visible also in other leaf tissues. This pattern became more pronounced in leaves treated with UV. Stem tissues did not show any GUS activity, while in tubers the GUS staining was observed in cortex under periderm and in vascular ring. In roots staining was localized in the root hair zone where rhizodermis and cortex cells are stained.