Yu, G., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States
Nguyen, T.T.H., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States
Guo, Y., Howard Hughes Medical Institute, Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology and Proteomics, La Jolla, CA 92037, United States
Schauvinhold, I., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States
Auldridge, M.E., Howard Hughes Medical Institute, Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology and Proteomics, La Jolla, CA 92037, United States, Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, United States
Bhuiyan, N., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States
Ben-Israel, I., Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food, and Environment, Hebrew University of Jerusalem, Rehovot 76100, Israel
Iijima, Y., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States, Department of Nutrition and Life Science, Kanagawa Institute of Technology, 1030 Shimo-ogino, Atsugi, Kanawaga 243-0292, Japan
Fridman, E., Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Food, and Environment, Hebrew University of Jerusalem, Rehovot 76100, Israel
Noel, J.P., Howard Hughes Medical Institute, Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology and Proteomics, La Jolla, CA 92037, United States
Pichersky, E., Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States

The trichomes of the wild tomato species Solanum habrochaites subsp. glabratum synthesize and store high levels of methylketones, primarily 2-tridecanone and 2-undecanone, that protect the plants against various herbivorous insects. Previously, we identified cDNAs encoding two proteins necessary for methylketone biosynthesis, designated methylketone synthase 1 (ShMKS1) and ShMKS2. Here, we report the isolation of genomic sequences encoding ShMKS1 and ShMKS2 as well as the homologous genes from the cultivated tomato, Solanum lycopersicum. We show that a full-length transcript of ShMKS2 encodes a protein that is localized in the plastids. By expressing ShMKS1 and ShMKS2 in Escherichia coli and analyzing the products formed, as well as by performing in vitro assays with both ShMKS1and ShMKS2, we conclude that ShMKS2 acts as a thioesterase hydrolyzing 3-ketoacyl-acyl carrier proteins (plastid-localized intermediates of fatty acid biosynthesis) to release 3-ketoacids and that ShMKS1 subsequently catalyzes the decarboxylation of these liberated 3-ketoacids, forming the methylketone products. Genes encoding proteins with high similarity to ShMKS2, a member of the "hot-dog fold" protein family that is known to include other thioesterases in nonplant organisms, are present in plant species outside the genus Solanum. We show that a related enzyme from Arabidopsis (Arabidopsis thaliana) also produces 3-ketoacids when recombinantly expressed in E. coli. Thus, the thioesterase activity of proteins in this family appears to be ancient. In contrast, the 3-ketoacid decarboxylase activity of ShMKS1, which belongs to the α/β-hydrolase fold superfamily, appears to have emerged more recently, possibly within the genus Solanum. © 2010 American Society of Plant Biologists.