Structure of the Parsley Caffeoyl-CoA O-methyltransferase Gene, Harbouring a Novel Elicitor Responsive Cis-acting Element

The sequence of the S-adenosyl-L-methionine:trans-caffeoyl-CoA O-methyltransferase (CCoAOMT, EC2.1.1.104) gene, including the 5'-flanking region of 5 kb, was determined from parsley (Petroselinum crispum) plants. The enzyme appears to be encoded by one or two genes, and the ORF is arranged in five exons spaced by introns from 107 to 263 bp in length. The genomic sequence matches the ORF of the cDNA previously reported from elicited parsley cell cultures, showing only three base changes that do not affect the enzyme polypeptide sequence. S1 nuclease protection assays and primer extension analyses with genomic and cDNA templates revealed the transcription start site 67 bp upstream of the translation start codon, indicating a shorter 5'-UTR than reported previously for the transcript. Promoter regulatory consensus elements such as two 'CAAT' boxes and one 'TATA' box were identified at -196, -127 and -31, respectively, relative to the transcription start site, and an SV 40-like enhancer element is located 347 bp upstream. Most notably, three putative cis-regulatory elements were recognized by sequence alignments, which represent motifs recurring in the promoters of several genes of the stress-inducible phenylpropanoid pathway (boxes P, A and L). Transient expression assays with a set of 5'-truncated promoter-GUS fusions show that significant promoter activity is retained in a 354 bp promoter fragment. In vitro DNase 1 footprint experiments and electrophoretic mobilty shift assays (EMSA) identified in this fragment a unique sequence motif with elicitor-inducible trans-factor binding activity, which was unrelated to boxes P, A, or L. This novel cis-regulatory element, designated box E, appears to be conserved in the TATA-proximal regions of other stress-inducible phenylpropanoid genes, and in vitro binding of nuclear protein was confirmed in EMSA assays for such an element from the PAL-1 promoter (-54 to -45). Moreover, the deletion of box E reduced the activity and erased the elicitor-responsiveness of the CCoAOMT promoter in transient expression assays. The results corroborate the proposed physiological function of CCoAOMT in elicited plant cells and may shed new light on the sequential action of trans-active factors in the regulation of phenylpropanoid genes.