Distinct cold responsiveness of a StInvInh2 gene promoter in transgenic potato tubers with contrasting resistance to cold-induced sweetening.

Potato (Solanum tuberosum L.) vacuolar invertase (β-fructofuranosidase; EC 3.2.1.26) inhibitor 2 (StInvInh2) plays an important role in cold-induced sweetening (CIS) of potato tubers. The transcript levels of StInvInh2 were increased by prolonged cold in potato tubers with CIS-resistance but decreased in potato tubers with CIS-sensitivity. However, the transcript regulation mechanisms of StInvInh2 responding to prolonged cold are largely unclear in CIS-resistant and CIS-sensitive genotypes. In the present study, the 5'-flanking sequence of the StInvInh2 was cloned, and cis-acting elements were predicted. No informative differences in StInvInh2 promoter structure between resistant and sensitive-CIS potato genotypes were observed. Histochemical assay showed that the promoter of StInvInh2 mainly governed β-glucuronidase (GUS) expression in potato microtubers. Quantitative analysis of GUS expression suggested that StInvInh2 promoter activity was enhanced by prolonged cold in CIS-resistant genotype tubers but suppressed in CIS-sensitive tubers. These findings provide essential information regarding transcriptional regulatory mechanisms of StInvInh2 in cold-stored tubers contrasting CIS capacity.