Functional characterization of amyrin synthase involved in ursolic acid biosynthesis in Catharanthus roseus leaf epidermis.
Catharanthus roseus accumulates high levels of the pentacyclic triterpene, ursolic acid, as a component of its wax exudate on the leaf surface. Bioinformatic analyses of transcripts derived from the leaf epidermis provide evidence for the specialized role of this tissue in the biosynthesis of ursolic acid. Cloning and functional expression in yeast of a triterpene synthase derived from this tissue showed it to be predominantly an α-amyrin synthase (CrAS), since the α-amyrin to β-amyrin reaction products accumulated in a 5:1 ratio. Expression analysis of CrAS showed that triterpene biosynthesis occurs predominantly in the youngest leaf tissues and in the earliest stages of seedling development. Further studies using laser capture microdissection to harvest RNA from epidermis, mesophyll, idioblasts, laticifers and vasculature of leaves showed the leaf epidermis to be the preferred sites of CrAS expression and provide conclusive evidence for the involvement of this tissue in the biosynthesis of ursolic acid in C. roseus.
Department of Biological Sciences, Brock University, St. Catharines, ON, Canada. fyu@brocku.ca
Fang
F
Yu
Antje M K
AM
Thamm
Darwin
D
Reed
Nemesio
N
Villa-Ruano
Alfonso Lara
AL
Quesada
Edmundo Lozoya
EL
Gloria
Patrick
P
Covello
Vincenzo
V
De Luca
D030008:Catharanthus / Q000201:enzymology*; D019751:Intramolecular Transferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008968:Molecular Conformation; D019441:Plant Epidermis / Q000201:enzymology*; D018515:Plant Leaves / Q000201:enzymology*; D014315:Triterpenes / Q000737:chemistry / Q000378:metabolism*; D000097245:Ursolic Acid
D019751:Intramolecular Transferases; D014315:Triterpenes; D000097245:Ursolic Acid; C039924:2,3-oxidosqualene-beta-amyrin-cyclase