Structure and function of the promoter of the carrot V-type H(+)-ATPase catalytic subunit gene

We investigated the 5'-upstream region of the gene encoding the catalytic subunit of the V-type H(+)-ATPase in Daucus carota. A genomic sublibrary was screened with a cDNA probe, and a 4-kilobase genomic clone was obtained covering the first two exons and about 3 kilobases of the 5'-upstream sequence. The intron/exon boundaries matched established consensus sequences. Within 240 base pairs (bp) upstream of the initiation codon three putative TATA boxes were found. Ribonuclease protection and primer extension analysis indicated that the three TATA boxes corresponded to two major and one minor transcription start sites. The flanking sequences of the two more proximal TATA boxes were nearly identical. Additional sequence motifs with putative regulatory function are two CCAAT boxes, an Sp1-binding consensus sequence, and long (TATA)n stretches within 800 bp of the 5'-upstream sequence. Transcriptional fusions to the beta-glucuronidase reporter gene were made for two different promoter constructs, and the resulting plasmids were mobilized into Agrobacterium tumefaciens. The analysis of beta-glucuronidase activities in the transformed carrot calli showed that 240 bp of the upstream sequence, including all three TATA boxes, led to low but detectable beta-glucuronidase expression; however, the larger construct, which included the putative Sp1-binding sequence and the (TATA)n stretches, led to an approximately 6-fold higher beta-glucuronidase expression. Histochemical analysis of beta-glucuronidase activity in the transformed calli showed no preferential expression in any specific cell type, in keeping with the presumed "housekeeping" character of the V-type H(+)-ATPase catalytic subunit gene.