Novel cis-acting elements in Petunia Cab gene promoters

In order to identify specific cis-acting elements which regulate the expression of the divergent Cab22R and Cab22L genes of Petunia, we conducted systematic mutational studies of the 1 kb intergenic promoter region. Sequence analysis revealed three GATA box sequence repeats positioned between the TATA and CAAT box elements. These GATA elements are conserved in corresponding promoter regions of all LHCII Type I Cab genes in Petunia and other dicotyledonous plants we have examined. Site-specific mutations in the CAAT box and the GATA box elements of the Cab22R promoter resulted in 8-fold and 5-fold reductions in Cab22R transcript levels respectively. A deletion of 52 bp, adjacent and upstream from the CAAT box (-92 to -145) in the Cab22R promoter reduced transcript levels 20-fold. This deletion contains a region of 13 bp which is conserved between many Petunia Cab genes. These results indicate that the quantitative expression of the Cab22 promoters is regulated by multiple cis-acting elements including CAAT and GATA box elements as well as sequences located between -92 and -145. The deletion of the region between -92 and -145 is partially compensated by homologous sequences present in the adjacent divergent promoter Cab22L.