Biology Reference
In-Depth Information
species (Snow et al. 2001). Other species known to exhibit this potential
include quinoa (
Chenopodium quinoa
) (Wilson and Manhart 1993),
squashes (
Cucurbita
spp.), maize (
Zea mays
), wheats (
Tr iticum
spp.), rice
(
Oryza
spp.), soybean (
Glycine max
), barley (
Hordeum vulgare
), cotton
(
Gossypium
spp.), millets (
Eleusine
and
Setaria
spp.), beans (
Phaseolus
spp.),
and sugar cane (
Saccharum officinarum
) (Ellstrand et al. 1999;Wilson 1990).
Transgenes and Microorganisms
The potential also exists for transfer of transgenes from crops to microor-
ganisms and among microorganisms themselves. Oilseed rape (
Brassica
napus
) carrying an antibiotic resistance gene was found to transfer the
gene to
Aspergillus niger
,a soil fungus (Hoffman et al. 1994). Recent stud-
ies of bacterial genomes have shown that many bacterial genes are subject
to horizontal gene transfer, that is, exchange between different bacterial
species (Smalla and Sobecky 2002). Genetically engineered bacteria intro-
duced into soil microcosms have been shown to transfer engineered genes
to other soil bacteria (Doyle et al. 1995). RNA transgenes for plant resist-
ance to specific viruses can also be incorporated into the genome of cer-
tain viruses by recombination (Greene and Allison 1994;Tepfer 2002).
The behavior of transgenic microorganisms in the environment is still
poorly understood. How transgenic viruses designed to attack insect pests
behave depends on such factors as virulence, effectiveness of transmission
between host organisms, survival over periods of host inactivity, and other
factors (Dushoff and Dwyer 2001).Transgenic bacteria have been found to
influence soil ecology in ways that are unsuspected (Doyle et al. 1995;
Holmes and Ingham 1995).Transgenic forms can compete with indigenous
microorganisms, modify metabolic processes in the soil, alter the commu-
nity composition of the soil biota, influence symbiotic relationships
between microorganisms and higher plants, and introduce novel metabolic
products into the soil system. A potential also exists for rapid evolution of
many microorganisms carrying transgenes, especially under conditions of
environmental stress; consequences are difficult to predict (Velkov 2001).
Ecological Implications of Transgene
Escape from Crop Plants
The release of domesticated plants with transgenes has major ecological
implications. A potentially serious consequence is invasion of natural
communities by transgenic crop plants or the creation of highly invasive
