Biomedical Engineering Reference
In-Depth Information
TABLE 10.3
Strategies to Obtain Transgenic Tomato Plants with Longer Shelf Life
and Better Taste
Strategy
Description
Ref.
Inhibition of ethylene
formation
Chimeric gene construction under the control of the constitutive
35S CaMV promoter which encoded the anti-sense RNA of
1-aminocyclopropane-1-carboxylic acid (ACC) oxidase
12
A bacterial gene, the ACC deaminase (ACCD) which degrades
ACC, precursor of ethylene
21
Use of bacteriophage-T3-encoded S-adenosylmethionine
hydrolase (SAM), which degrades SAM, precursor of ethylene
21
Transwitch technology: the gene of interest is duplicated,
inserting an exact copy of the gene back into the plant
producing the inhibition of the translation of RNA into protein
21
Inhibition of
polygalacturonase enzyme
(softening enzyme)
Chimeric gene construction under the control of the constitutive
35S CaMV promoter which encoded the anti-sense RNA of
polygalacturonase
12
degrade ACC, the immediate precursor of ethylene synthesis, which also significantly
decreased ethylene biosynthesis.
21,25
The enzyme able to degrade ACC is called ACC
deamidase (ACCD).
21
The reduced level of ethylene was accompanied by a 2-week
delay in fruit ripening, which clearly has commercial potential. The general appear-
ance of the tomato fruit, apart from the delay in ripening, was completely normal
when compared to control experiments.
12
On the other hand, researchers at Agritope
(Beaverton, OR) have chosen to interfere with ethylene biosynthesis by focusing on
SAM hydrolase expression. Their first experiments in tobacco used bacteriophage-
T3-encoded SAM hydrolase to generate transgenic plants with a reduced capacity
to synthesize ethylene. Afterwards, they switched to tomatoes. With the goal of
obtaining stage-specific and tissue-specific SAM hydrolase gene expression, the
scientists employed tomato's E8 promoter. The native E8 gene is only expressed in
ripening fruit beginning at the mature green stage. It worked: SAM hydrolase
expression was indeed restricted to ripening fruit. Then they examined the genetic
construct's effect on post-harvest ripening. The goal was to slow down fruit ripening
or even stop it at a certain stage until the fruit was ready for shipping.
21
Approaching the ethylene pathway from a slightly different angle is DNA Plant
Technology (DNAP, Cinnaminson, NJ), which has developed a technology it terms
transwitch. In transwitch technology, the gene of interest is duplicated; inserting an
exact copy of the gene back into the plant appears to inhibit the translation of RNA
into protein, but that effect is not well characterized.
4,21
DNAP researchers have also
been developing an improved tomato using somaclonal variation, a method based
on culturing plant somatic cells to generate single gene mutations, chromosomal
variants, and changes in multi-gene traits. The company has field tested a somaclonal
tomato that can be harvested just as the first shades of pink start to appear. Ripening
proceeds after harvest without ethylene.
21
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