The Expression of the Maize Sucrose-Phosphate Synthase Gene in Lycopersicon esculentum: A Focus on the Effects of Breeding Transgenic Tomato Lines to a Wild-type Cultivar
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Authors
Lyman, Jamie S.
Issue Date
1997
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Sucrose-phosphate synthase (SPS) is a photosynthetic enzyme which
regulates sucrose synthesis by catalyzing the conversion of fructose 6-
phosphate and UDPglucose to sucrose phosphate. Because SPS is involved in
sucrose production, it is thought to be one of the key enzymes in the interface
between photosynthesis and starch-sucrose partitioning. In the hopes of
increasing fruit yield by causing increased partitioning of photosynthate
product to sucrose, Calgene, Inc. inserted a maize SPS gene into a tomato
cultivar.
However, two studies of tomato plants containing the maize SPS gene
fail to clearly indicate the influence of increased SPS expression on fruit yield.
Because these studies were conducted under different growth conditions
using different generations of transgenic tomatoes, the conflicting results may
be caused either by environmental or by genetic factors.
In order to increase the genetic uniformity between the plants studied,
the transgenic tomato plants were back-crossed to the wild-type cultivar
which lacked the maize gene insert. This study explored the effects of backcrossing
on the expression of the maize SPS gene by growing the progeny of
back-crossed tomato plants both in the lab and in field plots. SPS activity was
measured at two stages of the transgenic plants' life cycle using Vmax
enzymatic assays. SPS levels in wild-type plants were also measured in order
to determine the levels of endogenous tomato SPS activity. These
measurements were then compared to the activity levels in the transgenic
plant lines.
Assuming that the maize SPS gene is stably inherited, we proposed that
the gene expression should correspond to expected genotypic ratios. In three
of the five transgenic lines studied, significantly more plants exhibited wildtype
(low) levels of SPS activity than expected. In addition, all of the
transgenic lines showed a developmental shift toward wild-type SPS activity
levels. Earlier studies of maize SPS gene expression in tomato plants
indicated that the gene was both stably inherited and expressed in predictable
activity ranges. Although traditional thought maintained that back-crossing
does not alter expression patterns, the data from this research indicates that
backcrossing to a wild-type cu1tivar may either disrupt the stability of the
maize gene inheritance or enable the tomatoes to regulate maize SPS gene
expression.
Description
vii, 28 p.
Citation
Publisher
Kalamazoo College
License
U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder.