Wound-inducible potato inhibitor II genes: enhancement of expression by sucrose.

Expression of a chimeric potato Inhibitor II-CAT gene in transgenic tobacco plants was enhanced 50-fold when leaf tissue was floated on solutions containing 1% sucrose. The expression of the chimeric gene was also enhanced when leaf sections were floated on solutions of glucose, fructose, and maltose, but not when floated on solutions of mannitol. The increased expression due to sucrose was found to be correlated with an increase in CAT mRNA. Thus, the carbohydrates or their metabolic products may control Inhibitor II gene expression by regulating transcription. Levels of potato Inhibitor II proteins in leaf sections from young potato plants floated on 3% sucrose solutions increased 3-fold compared to leaf sections floated on water, supporting the possibility that sucrose may have a role in regulating or enhancing the expression of wound-inducible proteinase inhibitor genes in potato tissues. It is suggested that the Inhibitor II gene and perhaps other genes regulated by sucrose may contain a specific 'sucrose enhancer' that strongly increases transcription of genes already active at low levels.