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Engineering fungal resistance in rice

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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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