Basel, Switzerland
February 8, 2008
By Tanuja Rohatgi,
Checkbiotech
A good agricultural harvest is not
only dependent on favorable weather conditions, but also on
remaining unscathed by insects and disease. That is why the work
of three universities with rice could prove to be very
beneficial.
Often a considerable amount of crop yield is lost due to
infection from plant pathogens. Fungi are the largest group of
plant pathogens. They can infect almost all crop varieties. One
fungus responsible for extensive damage to rice crop is
Magnaporthe grisea. M. grisea causes the most devastating damage
of rice crops worldwide, Rice Blast.
However, using genetic engineering,
Dr. Min Shao and his
collaborators at Nanjing
Agricultural University, Nanjing, China, North Carolina
State University, Raleigh, USA and Huazhong Agricultural
University, Wuhan, China were successful in incorporating genes
into rice varieties that are responsible for triggering natural
plant defense mechanisms. The end result yielded a rice variety
that effectively protects against several plant pathogens. Their
work is published in a recent issue of
Plant
Biotechnology Journal.
Most of plant pathogens are constantly evolving, which makes the
task of controlling them a difficult one. Since researchers
cannot predict how fast and when pathogens will evolve, the
process of developing resistant varieties can be a never ending
task with limited and short-term benefits.
With that in mind, the researchers were interested in finding a
long term solution that not only protected against Rice Blast,
but other pathogens as well. Dr. Shao and his group came upon
the novel idea of developing a genetically modified rice variety
that possessed resistance to a wide range of existing and future
plant pathogens.
Bacteria to the rescue
Although bacteria also infect crops and cause severe damage to
them, they also produce Harpin, a protein capable of eliciting
disease and insect resistance in plants. Dr. Shao decided to
exploit the potential of Harpin as a natural initiator of the
plants’s own defense systems against invading pathogens.
The researchers introduced the gene for harpin (hrf1) into the
rice genome and generated a genetically engineered rice variety
with enhanced resistance against M. grisea. Since M. grisea
infects plants through the leaves, it was encouraging to find
that the amount of harpin increased in the leaves of transgenic
rice during the growing season. Thus, Dr. Shao’s transgenic rice
is capable of protecting itself against M. grisea infection.
It is good to see a strategy working, but what makes it all the
more motivating is to find out the reason behind it. The
researchers found out that the presence of the hrf1 gene in
transgenic rice increases leaf silicon concentration. According
to them, this might be responsible for inhibition of specialized
structures required by fungus to penetrate rice leaves.
Fields vs Indoors
To realize the ultimate aim of developing transgenic rice for
growing in open fields, Dr. Shao’s group tested the ability of
their transgenic rice under natural environmental conditions and
also in closed supervised nurseries. Unlike non-GM rice, the GM
rice grew successfully under both closed and open field
conditions.
The researchers correlated the increase in resistance in
transgenic rice with the accumulation of harpin protein as plant
mature. The researchers emphasize that their present results
have laid the groundwork for their future experiments, which
will assess the durability of this technique.
Dr. Ralph Dean, one of the authors of the study told
Checkbiotech, “There are many examples of transgenic crops being
used successfully, but much more work will have to be done
before rice plants expressing harpin genes would ever be ready
for distribution.”
Dr. Dean went on to further explain that, “Harpin is a natural
product produced by bacteria and would not appear likely to be
noxious, although again this would have to be carefully tested.”
One question that is always raised when dealing with genetically
modified crops is the possibility of them crossing with wild
varieties. “It is understandable that the public may have
concerns regarding transgenic crops, but rice generally does not
outcross, but it is possible to cross with wild-species such as
red rice,” said Dr. Dean, “However, the viability of these
hybrids is likely to be poor, otherwise the species would have
crossed in the past and the hybrids would predominate in
nature.”
Despite his cautionary approach Dr. Dean is quite optimistic,
“The beauty of harpin is that it activates the plants own
natural defense mechanisms. Thus, if harpin is safe and other
safeguards are in place, I believe this strategy has a lot of
potential for use against many pathogens and in other crops.”
Tanuja Rohatgi is a Science Writer for Checkbiotech in Basel,
Switzerland.
Publication:
Shao M, Wang J, Dean RA, Lin Y, Gao X, Hu S.
Expression of a harpin-encoding gene in rice confers durable
nonspecific resistance to Magnaporthe grisea.
Plant
Biotechnology Journal. 2008 Jan; 6(1):73-81
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