Plant immune system research ready for application
To combat pathogens, farmers rely on disease-resistant plant varieties--cultivated by careful, slow breeding--and pesticides. Both are far from foolproof. Pathogens evolve to outwit breeding and pesticides often carry harmful environmental side effects. Some farmers, like those in developing countries, also can't afford them. Creating disease resistant seeds, requiring little-to-no pesticides and no unfamiliar agricultural techniques, is "a simple and effective way to help farmers in developing countries," Horvath said.
Classical breeding has given plant researchers a wealth of genetic material, developed over generations, with which to breed disease resistant varieties. Combined with leaps and bounds in genetics research and quicker, cheaper DNA sequencing, scientists have learned how to build stronger plant varieties. They have pinpointed special receptors, housed both inside and outside plant cells, which scan for infection; launching the attack when a pathogen is found. They've identified disease-resistant genes housed in the molecular architecture of different plants. These genes can confer resistance to dangers such as wheat rust, powdery mildew and bacterial spot disease.
"We now know enough about the key molecules in the plant immune system that we can actually start to deploy what we've learned," said Dangl. This includes genetic editing--removing disease-prone genes--or mining disease-resistance genes from various plants and adding them into other crops. Combining a few disease-resistance genes would bolster plant immunity to multiple diseases, similar to the chemical cocktail developed to fight AIDS.
The ultimate objective is to build "predictive, highly refined molecular plant breeding that includes disease resistance," Dangl said. It's essentially an updated version of classical breeding, injecting genetic know-how into seed creation using disease-resistance genes from plants people eat every day: wheat, rice, pepper, tomato and others.
This has already been successful. Disease resistance genes bred into papaya helped save Hawaii's papaya industry from a ringspot virus in the mid-90s. Staskawicz and Horvath also worked to develop tomato plants resistant to bacterial pathogens. In Florida field tests, the modified varieties have higher yields and don't require harmful copper pesticides.
Still, researchers have much to learn. How all these disease resistance genes function, on a molecular basis, is to be discovered. Staskawicz compares it to watching TV. You know if you press a certain button, the TV comes on, without understanding any mechanics behind the screen. "You can still use the gene without knowing exactly how it works," he said. Pathogens will also continue evolving, slowly subverting genetic disease resistance, engineered or not. "It's a constantly evolving process," Staskawicz said.
There are no simple solutions, said Michael Mishkind, a program director in NSF's Biological Sciences Directorate. Yet our current level of understanding of disease resistance mechanisms "speaks eloquently to the importance of basic research. Years of fundamental study of the plant immune system have added a powerful set of tools, helping us keep ahead of the pathogens that threaten our food supply."
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