Transgenic barley plants over-expressing a zinc transport protein
had smaller seeds and did not accumulate more zinc when grown in
zinc-deficient soil.
Manipulated Organism:
Barley (Hordeum vulgare).
Inserted Transgenes:
AtZIP1 and AtZIP3, which are genes for zinc transport
proteins from the mustard plant Arabidopsis thaliana. The DNA
constructs contained one of the AtZIP genes under the control
of the maize ubiquitin promoter as well as a gene for resistance to the
antibiotic hygromycin under the control of the cauliflower mosaic virus
35S promoter.
Goal of This Study:
"Increasing the zinc content of cereal grains will be important for
improving human nutrition. Improved plant zinc efficiency will lead to
increased yields when available zinc is limiting plant growth. The aim
of our work was to test how the over-expression of zinc transporters in
cereals affects plant growth, seed mineral content, and zinc transport
rates" (p. 373).
Intended Effect:
-
A number of transgenic barley lines were created with levels of ZIP1
RNA much higher than in the parent. (With the techniques they used, the
authors couldn't determine how much of the ZIP1 RNA was produced by the
transgene and how much was produced by barley's own version of the
AtZIP1 gene.)
-
When deprived of zinc for 12-24 hours under hydroponic conditions
and then resupplied, the transgenic lines over-expressing ZIP1 took up
zinc 2-3 times more quickly than the parent.
-
Some transgenic lines grown in a zinc-sufficient potting mix produced
seeds with a zinc concentration 2-3 times greater than in seeds
from the parent line.
Unintended Effects:
-
While both the AtZIP1 and AtZIP3 genes were introduced into
the barley cultivar Golden Promise, the authors state that only
AtZIP1 yielded a transgenic line of barley (p. 380). No rationale
was given for this result.
-
In the second transgenic generation, some of the descendants of the
trangenic lines had little to no detectable ZIP1 RNA. According to the
authors, "These low levels were either due to silencing of the transgene
and endogenous gene or due to loss of the transgene from segregation"
(p. 377). Despite the appearance of low ZIP1 expression, these plants
also showed elevated levels of zinc uptake following zinc deprivation,
although not as much as the ZIP1 over-expressing plants.
-
Under zinc-sufficient conditions in the hydroponic experiment, no
differences in zinc uptake were observed between the parent and
transgenic lines.
-
Seeds from several different transgenic lines were 20-30% lighter
than seeds from the parent line.
-
After 40 days of growing in zinc-deficient sand, the transgenic lines
suffered just as much reduction in their foliar zinc level as the
parent line.
Source:
Ramesh, S. A., S. Choimes, and D. P. Schachtman (2004). "Over-Expression
of an Arabidopsis Zinc Transporter in Hordeum vulgare
Increases Short-Term Zinc Uptake after Zinc Deprivation and Seed Zinc
Content," Plant Molecular Biology vol. 54, pp. 373-85.
Author Affiliations:
CSIRO Plant Industry, Australia.
Funding:
Not mentioned.
Product Status:
Not on the market as of 2009.
Copyright 2009 The Nature
Institute.
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