Marker-assisted breeding comes of
DNA LandMarks Inc.
article* posted here on SeedQuest last year declared the
10th anniversary for marker-assisted selection. In the article,
scientists from Pioneer Hi-Bred
described how, in the early days, they were quite happy to
screen 10,000 plants a year with DNA markers. Today they
routinely screen over 1 million plants annually. Furthermore,
they felt they had only seen the tip of the iceberg in terms of
this technology’s potential.
In fact genetic markers go back
further than 10 years. In plants the technology started to
develop in the 1980’s. Even in those seminal days, scientists
understood the tremendous potential that existed in mapping the
genomes of living organisms. Primarily they were excited about
the possibility to find genes of interest and then track them
reliably through generations of crosses.
Over the past two decades, there
have been many advances and applications of markers in plant
breeding. There are countless markers that have been found
closely linked to traits of interest and these are now used to
screen plants for disease resistance, quality characteristics,
etc. Markers are also routinely used for fingerprinting lines
both as part of breeding work and for variety protection once
material is commercially released.
ABI 3730XL DNA
analyzer for DNA sequencing and SNP genotyping
handling system for liquid handling.
Yet for all of the work that has
been done, marker technology has remained relatively obscure to
the general public. Ask someone on the street what they think
of GMOs and not only will they know what you are talking about
but they will probably have a strong opinion either pro or con
on the technology. Ask the same person what they think of
marker-assisted breeding and they will just look at you
However, a revolution seems to be
in progress. These days genetic markers are receiving
considerably more attention. Recent presentations by both
have trumpeted marker-assisted breeding as a key plank in their
R&D strategy. Some of these presentations even refer to it as a
“new technology”. In a July
article** in the
Washington Post, long time GMO foe Jeremy Rifkin wrote with
cautious optimism about the “new frontier” of genomics and how
it will render genetic engineering “obsolete”.
So why are people only now
discovering the importance of a technology that has been with us
for about 20 years? The two main reasons are the cost of the
technology and the complexity of the traits being sought.
In some ways genetic marker
technology has mirrored computer technology in its development
arc. Each development cycle reduces costs dramatically while at
the same time increasing the power of the technology. Isolating
DNA from plant tissue was once a cumbersome affair and seemed as
much alchemy as true science. Likewise, early DNA markers were
mostly based on RFLP (restriction fragment length polymorphism)
technology which was slow and expensive to run.
Today tiny leaf disks can be
clipped from breeding nurseries scattered around the globe,
dried and shipped to a high-throughput lab for DNA robotic
extraction and analysis. Detection methods have evolved to the
point where only very small amounts of template DNA are required
and changes as small as a single nucleotide can be detected.
Furthermore, thousands of these reactions can be run in
parallel. All of these changes have resulted in the reaction
costs dropping from several dollars to several cents each. Such
dramatic cost reductions have not only made marker-assisted
breeding economically feasible, it has become strategically
imperative to keep companies competitive.
The second factor in marker
technology’s rise in prominence has to do with trait
complexity. To understand why this is important, we first need
to look at genetic engineering. This technology is very
effective at moving single gene traits from one organism to
another. Today it is also routine to “stack” a number of these
traits into a single variety. Despite Jeremy Rifkin’s
predictions, genetic engineering is still an important tool in
agricultural biotechnology and will likely remain so for the
However, most important agronomic
traits (e.g. yield, drought tolerance, nitrogen use efficiency)
are not controlled by a single gene. Instead they are run by
complex interactions amongst numerous genes. Not only are these
traits dependent on the presence of the right alleles of these
genes, but in most cases the levels of expression of the genes
are also key to obtaining the best possible performance.
Genetic engineering technology
has not evolved to the point where these complex, multigenic
traits can be reliably spliced from one organism to another.
However by using genetic markers it is possible to analyze the
various genetic components that contribute to a complex trait.
These components are unique loci in the genome and analyzing
their individual contribution to a trait is known as
quantitative trait loci or QTL analysis.
QTL analysis is where the
greatest potential of marker technology lies. This is why
leading agricultural biotech companies are starting to talk up
their marker programs to customers and the investment
community. We have reached a confluence point of cost and
technology that will allow us to manage very complex and highly
valuable traits. By using genetic markers, researchers and
breeders will be able to find rare combinations of alleles at
multiple loci that deliver maximum genetic performance. Plant
breeding has always been a numbers game. Genetic markers will
serve to better the breeders’ odds tremendously.
Key agricultural productivity technology arrives at 10-year
milestone: marker-assisted selection has revolutionized how
scientists increase crop performance with native crop genes
Beyond genetically modified crops, Jeremy Rifkin, July 4,
A world leader in DNA marker development and
applications, DNA LandMarks Inc. offers a full array of marker
technologies to the agricultural sector from development to
mapping to high-throughput application.
Charles Pick can be reached