PLANT PHYSIOLOGY , Vol 112, Issue 1 311-318, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characterization of Novel Sesquiterpenoid Biosynthesis in Tobacco Expressing a Fungal Sesquiterpene Synthase
M. Zook, T. Hohn, A. Bonnen, J. Tsuji and R. Hammerschmidt
Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824 (M.Z., A.B., J.T., R.H.)
The gene encoding trichodiene synthase (Tri5), a sesquiterpene synthase
from the fungus Fusarium sporotrichioides, was used to transform tobacco
(Nicotiana tabacum). Trichodiene was the sole sesquiterpene synthase
product in enzyme reaction mixtures derived from unelicited transformant
cell-suspension cultures, and both trichodiene and 5-epi-aristolochene were
observed as reaction products following elicitor treatment. Immunoblot
analysis of protein extracts revealed the presence of trichodiene synthase
only in transformant cell lines producing trichodiene. In vivo labeling
with [3H]mevalonate revealed the presence of a novel trichodiene
metabolite, 15-hydroxytrichodiene, that accumulated in the transformant
cell-suspension cultures. In a trichodiene-producing transformant, the
level of 15-hydroxytrichodiene accumulation increased after elicitor
treatment. In vivo labeling with [14C]acetate showed that the biosynthetic
rate of trichodiene and 15-hydroxytrichodiene also increased after elicitor
treatment. Incorporation of radioactivity from [14C]acetate into capsidiol
was reduced following elicitor treatment of a trichodiene-producing
transformant as compared with wild type. These results demonstrate that
sesquiterpenoid accumulation resulting from the constitutive expression of
a foreign sesquiterpene synthase is responsive to elicitation and that the
farnesyl pyrophosphate present in elicited cells can be utilized by a
foreign sesquiterpene synthase to produce high levels of novel
sesquiterpenoids.
