Cloning and functional characterization of a phenolic acid decarboxylase from the liverwort Conocephalum japonicum.

Some commercially important vinyl derivatives are produced by the decarboxylation of phenolic acids. Enzymatically, this process can be achieved by phenolic acid decarboxylases (PADs), which are able to act on phenolic acid substrates such as ferulic and p-coumaric acid. Although many microbial PADs have been characterized, little is known regarding their plant homologs. Transcriptome sequencing in the liverworts has identified seven putative PADs, which share a measure of sequence identity with microbial PADs, but are typically much longer proteins. Here, a PAD-encoding gene was isolated from the liverwort species Conocephalum japonicum. The 1197 nt CjPAD cDNA sequence was predicted to be translated into a 398 residue protein. When the gene was heterologously expressed in Escherichia coli, its product exhibited a high level of PAD activity when provided with either p-coumaric or ferulic acid as substrate, along with the conversion of caffeic acid and sinapic acid to their corresponding decarboxylated products. Both N- and C-terminal truncation derivatives were non-functional. The transient expression in tobacco of a GFP/CjPAD fusion gene demonstrated that the CjPAD protein is expressed in the cytoplasm. It is first time a PAD was characterized from plants and the present investigation provided a candidate gene for catalyzing the formation of volatile phenols.