Alfalfa with corn transgenes for anthocyanin (red-purple pigment)
production was not visibly altered or changed dependent on light and
temperature conditions.
Manipulated Organism:
Alfalfa (Medicago sativa).
Inserted Transgenes:
Three transgenic lines of alfalfa were produced by introducing either
Lc, B-Peru, or C1. All three genes are anthocyanin
regulatory genes from maize (Zea mays). In maize, Lc
(leaf color) induces the expression of enzymes that form red anthocyanin
pigments in several plant tissues. Lc was fused to the cauliflower
mosaic virus (CaMV-35S) promoter so that the gene was expressed in all
parts of the plant.
Goal:
Produce transgenic alfalfa with higher contents of anthocyanins and
proanthocyanidins in stems and leaves. Increased amounts of these
substances are meant to improve feed quality by preventing pasture bloat
in ruminant livestock and increasing the efficiency of conversion of
plant protein into animal protein.
Target Effect:
Transgenic Lc alfalfa synthesizes anthocyanins and
proanthocyanidins in natural sunlight and under greenhouse conditions
when subjected to high light intensity or cold.
Nontarget Effects:
-
Grown in moderate greenhouse conditions, Lc plants expressed abundant
transcripts of the transgene in their leaves. However, no anthocyanins or
proanthocyanidins accumulated under these conditions and the transgenic
plants were bright green.
-
Microscopically, there were more air spaces between cells.
-
Red color was visibly induced within hours in most Lc plants
when they were subjected to bright light or low temperatures, and within
three days the plants changed completely in color. The red color faded
quickly when these conditions were removed.
-
The flavone content in the leaves and stems of the Lc plants
was reduced. Flavones in the animal and human diet may reduce the risk
of some diseases (cancer, cardiovascular disease).
-
B-Peru transgenic and C1 transgenic alfalfa populations
showed no visible accumulation of the desired pigments, although the
inserted transgenes were expressed at detectable levels.
Additional Comments:
This study shows that anthocyanin production is "a function of
environmental conditions and transgene specificity" (p. 1456); in
other words it is highly context-dependent.
Source:
Ray, H., M. Yu, P. Auser, L. Blahut-Beatty et al. (2003). "Expression of
Anthocyanins and Proanthocyanidins after Transformation of Alfalfa with
Maize Lc," Plant Physiology vol. 132, pp. 1448-63.
Author Affiliations:
Saskatoon Research Centre, Agriculture and Agri-Food Canada; Plant
Biotechnology Institute, Saskatoon, Saskatchewan; University of Guelph,
Ontario; University of Texas, Austin.
Funding:
Supported in part by grants from the Alberta Agriculture Research
Institute, the Alberta Cattle Commission, and the Saskatchewan
Agricultural Development Fund.
Product Status: Not on the market as of 2008.
Copyright 2008 The Nature Institute.
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