Overexpression of phytoene synthase gene in Arabidopsis
resulted in delayed germination, increased levels of chlorophyll, and
changes in relative levels of carotenoids.
Manipulated Organism:
Arabidopsis (Thale Cress; mustard family).
Inserted Transgenes:
Multiple copies of the phytoene synthase gene from Arabidopsis,
fused to the seed-specific napA promotor from oilseed rape to
ensure that the genes are expressed in the seeds.
Goal:
Increase the production of carotenoids in the seeds of
Arabidopsis. The overall aim of this research is to engineer crops
in a way that their seeds become a commercial resource for carotenoids.
(See also: canola_001.)
Target Effect:
The transgenic Arabidopsis plants produced darker seeds, and
extracts from the seeds showed a 43-fold average increase in the amount
of beta-carotene. Significant amounts of lycopene and alpha-carotene
were also found.
Nontarget Effects:
-
The relative levels of the different carotenoids in the transgenic seeds
were strikingly different from the composition in seeds of unaltered
plants. For example, beta-carotene made up 28% of the carotenoids in
transgenic seeds while in the seeds of controls only 4%; lutein made
up 40% of carotenoids in the transgenic seeds and 61% in the seeds of
controls.
-
In the seeds of transgenic plants several known and unknown carotenoids
appeared that were not present in the seeds of the control plants.
-
The level of chlorophyll was increased, although the researchers had
expected a decrease.
-
Seeds from the transgenic plants exhibited delayed germination. The
carotenoid level was negatively correlated with germination.
Additional Comments:
The authors remark: "Some of the results are in sharp contrast to
results obtained from similar expression studies in canola. For example,
overexpression of a bacterial phytoene synthase resulted in an equal
increase of alpha- and beta-carotene amounts, whereas
the levels of violaxanthin and lutein remained unaltered (Shewmaker
et al. 1999). The increase of beta-carotene accumulation is
similar to the result obtained in this study. . . . A clear difference
in the accumulation of alpha-carotene was . . . found because
the Arabidopsis plants did not produce relative levels of
alpha-carotene as high as the canola seed. Even more intriguing is
the difference between the levels of chlorophyll. In Arabidopsis,
the levels of chlorophyll were significantly increased, and in canola
the levels were decreased. We have no explanation for this difference"
(p.783). To view the report on Shewmaker et al. 1999 click
here.
Source:
Lindgren, L. O., K. G. Stålberg, and A.-S. Höglund
(2003). "Seed-Specific Overexpression of an Endogeneous Arabidopsis
Phytoene Synthase Gene Results in Delayed Germination and Increased Levels
of Carotenoids, Chlorophyll, and Abscisic Acid," Plant Physiology
vol. 132, pp. 779-85.
Author Affiliations:
Department of Plant Biology, Swedish University of Agricultural Science,
Uppsala.
Funding:
Stiftelsen för Lantbruksforskning, Ulla och Curt Nicolins Stipendiefond,
and AstaCaroteneAB.
Product Status:
Not on the market as of 2008.
Copyright 2008 The Nature
Institute.
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