Co-Authors:
Kapteyn, J., Department of Plant Sciences, BIO5 Institute for Collaborative Bioresearch, University of Arizona, Tucson, AZ 85721, United States
Qualley, A.V., Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907, United States
Xie, Z., Department of Plant Sciences, BIO5 Institute for Collaborative Bioresearch, University of Arizona, Tucson, AZ 85721, United States, College of Pharmacy, University of Arizona, Tucson, AZ 85721, United States
Fridman, E., Faculty of Agricultural, Food Quality, and Environmental Sciences, Robert H. Smith Institute of Plant Sciences and Genetics, Hebrew University of Jerusalem, Rehovot 76100, Israel
Dudareva, N., Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907, United States
Gang, D.R., Department of Plant Sciences, BIO5 Institute for Collaborative Bioresearch, University of Arizona, Tucson, AZ 85721, United States
Abstract:
Methylcinnamate, which is widely distributed throughout the plant kingdom, is a significant component of many floral scents and an important signaling molecule between plants and insects. Comparison of an EST database obtained from the glandular trichomes of a basil (Ocimum basilicum) variety that produces high levels of methylcinnamate (line MC) with other varieties producing little or no methylcinnamate identified several very closely related genes belonging to the SABATH family of carboxyl methyltransferases that are highly and almost exclusively expressed in line MC. Biochemical characterization of the corresponding recombinant proteins showed that cinnamate and p-coumarate are their best substrates for methylation, thus designating these enzymes as cinnamate/p-coumarate carboxyl methyltransferases (CCMTs). Gene expression, enzyme activity, protein profiling, and metabolite content analyses demonstrated that CCMTs are responsible for the formation of methylcinnamate in sweet basil. A phylogenetic analysis of the entire SABATH family placed these CCMTs into a clade that includes indole-3-acetic acid carboxyl methyltransferases and a large number of uncharacterized carboxyl methyltransferase-like proteins from monocots and lower plants. Structural modeling and ligand docking suggested active site residues that appear to contribute to the substrate preference of CCMTs relative to other members of the SABATH family. Site-directed mutagenesis of specific residues confirmed these findings. © 2007 American Society of Plant Biologists.
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