Dr. Robin Cameron, a U of T botany professor, was published in the Sept. 26 issue of the journal Nature for her groundbreaking work on plant disease resistance, an aspect of plant biology that has been shrouded in mystery for decades.
In many plants, when leaves are attacked by a pathogen (a virus, bacterium, or fungus), a chemical signal is sent out to the rest of the plant, warning it of the invasion. The first leaf may become infected, but the rest of the plant becomes immune to the pathogen—and to many other diseases. This type of defence mechanism is known as systemic acquired resistance (SAR).
Farmers and gardeners have known about this phenomenon for ages and biologists have been searching for its molecular basis since 1950.
When a leaf is attacked, the plant sends out a chemical flare, like an emergency signal, to the rest of the plant. This chemical signal is then captured by specific receptors in the cell walls in other parts of the plant. The cells then begin the steps necessary to prevent any future infections. SAR is like vaccination, but better because the plant acquires resistance to a variety of pathogens.
Scientists are still trying to piece together the steps in the signal pathway, to identify which proteins are involved in the defence mechanism and the identity of the genes that control them. Cameron and her colleagues in the U.S. and the U.K. identified one protein in that pathway, called DIR1, as well as locating the gene that encodes it. It seems that DIR1 is involved in the long-distance signalling between infected and healthy cells in the plant. There is still a great deal unknown about this pathway, but the identification of the protein has important implications.
Scientists may one day be able to genetically engineer crop species with cloned copies of the DIR1 gene that are already “turned on,” that is, already set to produce the signal protein. Plants carrying this modification would be immune to diseases they have never come into contact with. The need for chemical fungicides and bacteriocides could hopefully be reduced.
Asked if she had any concerns over the ecological or genetic consequences of altering DIR1 or any other gene, Cameron replied that she had few if any concerns over the safety of genetically modified organisms (GMOs). “I don’t have too much concern over the [genetically altered] plants that are out there right now,” she said. “Some people are alarmed, especially by the insertion of genes from one species to another. So if we can modify already existing genes in a plant, I don’t see how that could really be a problem.”
As DIR1 is just one protein in a pathway, we are not yet at the level where we could raise fields of plants immune to infectious diseases. But, the research continues.
Photograph by Renate Hamilton
