Deletion analysis of a tobacco pollen-specific polygalacturonase promoter

Abstract

Deletion analysis of the promoter sequence of the tobacco gene encoding a pollen-specific polygalacturonase (Npg1) revealed several motifs related to the LAT52/56 and LAT56/59 boxes (Twell et al. 1991) and a 14 bp element with homology to the maize polygalacturonase promoter (Allen and Lonsdale 1993), termed the PG box. Deletion analysis also revealed a complex pattern of domains which increase or reduce promoter activity. In particular, deleton of the LAT52/56 and LAT56/59 box motifs resulted in significant reductions in expression giving weight to the idea that such sequences function as transcriptional positive regulatory elements. Deletion of sequences immediately 3′ to the LAT52/56 and LAT56/59 motifs fully restore promoter function, suggesting the presence of suppressor elements associated with these positive regulatory elements. Analysis of the deletion series allowed the promoter to be divided into four domains: a modulation domain (-744 to -362), a basic promoter (-362), a core promoter (-267) and a minimal promoter (-182). Two sequence elements, Eh-1 (22 bp) and Eh-2 (28 bp), were identified between -362 and -267. Deletion of these two unrelated sequence elements reduces the activity of the basic promoter to that of the core promoter, a level of activity which is retained by the minimal promoter. A background level of activity is reached when the promoter is reduced to -86. Therefore, the sequence between -182 and -86, which contains two LAT52/56 motifs and the PG box, contains sufficient information to direct efficient gene expression.