Tobacco plant fragrance altered following transformation with
terpene synthesis cDNA’s
By means of genetic modification, it is possible for plants
to make highly specific aromatic substances (terpenoids). This
is the conclusion of the thesis by
Plant Research
International employee Mazen K. El Tamer, for which he
obtained his doctorate from Wageningen University on 27 November
2002.
Combining molecular biological research with cell biology,
biochemistry and sensory research, El Tamer demonstrated the
possibility to make tobacco leaves smell differently via genetic
modification. El Tamer identified a number of enzymes which are
responsible for the production of monoterpenes, and then the
part of these enzymes responsible for the specific biochemical
reaction that they perform. This information offers the
potential to improve crops that produce specific terpenes,
whereby they will smell and/or taste better, or be resistant to
diseases or pests.
Citrus varieties are important crops economically. Their
notably pleasant taste and smell is partially caused by the
presence of terpenoids. These terpenoids may also play a role in
the resistance to threats such as insects and fungi. The enzymes
called terpene synthases are responsible for making terpenoids.
From lemon, El Tamer isolated DNA that codes for a number of
these enzymes. He then tested tobacco plants genetically
modified with this DNA. With the help of a human panel, El Tamer
proved that the smell of the genetically modified tobacco leaves
had indeed changed compared to the wild variety.
As a part of his research, El Tamer isolated, characterised
and described four new monoterpene synthases. Each is
responsible for the production of one specific monoterpene.
Using domain swapping experiments, it was possible to ascertain
the basis for the specific differences between the monoterpene
synthases. Domain swapping experiments involve the exchange of
fragments from two DNA’s. Repeated checks are made as to whether
the DNA still codes for an enzyme that is capable of making the
specific monoterpene. Via these experiments, El Tamer
ascertained a domain of 200 amino acidson the enzyme upon which
the product specification is based. He then suggested that just
2 amino acids differentially positioned on the enzymes are
important for that specific role.
El Tamer’s work has considerably enhanced our understanding
of the process of molecular regulation of monoterpene
biosynthesis in plants. Further research into the effects of
monoterpene synthesis may have major economic implications. The
aromatic substances could entail an important change to the
plants if, due to these terpenoids, they would become more
resistant to diseases and pests. Moreover, the aromatic and
flavouring industry is likely to have an interest in increasing
the production of certain terpenoids.
