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Autoimmunity in plants?

Can plants suffer from autoimmunity? The term is generally reserved for organisms with an adaptive immune system, but one of the speakers last night at the Keystone meeting on plant signaling and immunity described a scenario that she called "the plant world version of autoimmunity." Farmers as well as plant researchers have long known that every once in a while, when two healthy plants are crossbred, the offspring (called F1) is inexplicably sickly - maybe its leaves are necrotic, or maybe it

By | February 14, 2008

Can plants suffer from autoimmunity? The term is generally reserved for organisms with an adaptive immune system, but one of the speakers last night at the Keystone meeting on plant signaling and immunity described a scenario that she called "the plant world version of autoimmunity." Farmers as well as plant researchers have long known that every once in a while, when two healthy plants are crossbred, the offspring (called F1) is inexplicably sickly - maybe its leaves are necrotic, or maybe it doesn't flower, or fails to grow. linkurl:Kirsten Bomblies,;http://www.weigelworld.org/research/projects/naturalvariation/ a postdoc in the lab of Detlef Weigel of the Max Planck Institute for Developmental Biology, Tubingen, believes that's because those F1 plants happened to inherit a pair of incompatible alleles - each one is normal in itself, but the combination sends the immune system into overdrive. In her talk, Bomblies described experiments in 21 "sick" hybrid strains obtained from about 1500 intercrosses from 293 wild strains of Arabidopsis. Gene expression profiles of all the genes that differed between a sick hybrid and a parent showed that most of those genes had to do with responses to pathogens and stress. Sick hybrids also had a higher resistance to some common pathogens. The group did some complicated genetics on one of the most severely affected hybrid lines to narrow down the locus on each parent chromosome responsible for the phenotype. One of the two alleles linkurl:turned out to be a type of R gene,;http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050236 activated in response to specific pathogens. They still haven't identified the second one, but since that locus too contains several R genes Bomblies said she suspects one of them to be the culprit. A similar set of experiments she also described last night, on another severely affected hybrid, also suggest that key players in the phenotype are again R genes. The idea is that the two R genes trigger cellular defense mechanisms, but only when a specific allele of each is present. "The plants are getting sick because they're initiating an immune response," she said. Normally that response would be localized to the site of infection, but in the sickly hybrids, it happens in each cell. How or why these genes turn each other on is still mysterious. But one possibility, Bomblies told me later, may have to do with the guard hypothesis, a central theory in plant immunity that stipulates that R genes "guard" the plant by monitoring for cellular changes that might be induced by the presence of a pathogen. "Maybe these two R genes are competing for the same thing to guard," she speculated.
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