Tissue-specific signal(s) activate the promoter of a metallocarboxypeptidase inhibitor gene family in potato tuber and berry

The molecular basis of the differential expression of the GM7-type metalloc arboxypeptidase inhibitor (MCPI) genes in tuberizing (StMCPI) and non-tuber izing Solanum species (SbMCPI) was investigated. It was shown that the StMC PI is encoded by a gene family in Solanum tuberosum (potato), but SbMCPI mi ght be a single-copy gene in the non-tuberizing species Solanum brevidens. The StMCPI promoter shows evolutionary relatedness to the S. brevidens-deri ved SbMCPI and to the fruit-specific tomato promoter 2A11. Both StMCPI and SbMCPI promoter regions were able to confer tuber- and berry-specific expre ssion for the beta -glucuronidase reporter gene in potato suggesting that t he difference in MCPI gene expression is in trans regulatory factors betwee n the tuberizing and the non-tuberizing Solanum species. The MCPI promoters did not respond to metabolic, environmental or hormonal signals in leaves. Thus, the MCPI genes are regulated in a different way than the other known tuber-specific genes and potentially are suitable for biotechnological app lication in potato to provide specific transgene expression in tuber and be rry.