How the plant immune system can drive the formation of n...(g defense response mounted against patho...)
g defense response mounted against pathogens during a normal infection. The plant immune response typically involves the sacrifice of a few cells at and around the infection site. But in the wimpy hybrids, healthy tissue also suffered, despite there being no pathogen around. The hybrid plants apparently mistook their own cell s for dangerous germs.
Although the genes that determined the abnormal autoimmunity were different in most crosses, the researchers discovered that often only two genes were required to cause the necrotic hybrid response: one from the father, the other from the mother. In one case that the researchers studied in more detail, they found that the gene that causes necrosis only in hybrids, but not in the parents, is normally used to sense the presence of a pathogen. The scientists emphasize, however, that the hybrids are not the victims of malfunctioning genes. In contrast to many hereditary diseases, the necrosis is not due to each parent carrying a defective copy of the same gene; rather, there is a destructive interaction between two different genes, each of which evolved differently in the two parents. The genes on their own are harmless or even beneficial, since the parents are healthy. Only the combination of the altered gene variants creates problems. These types of genetic malfunction are ofte n known as Dobzhanshy-Muller incompatibilities, after the two giants of early modern genetics who first studied these necrotic hybrids in fruit flies.
The results of the German-American team challenge the classical definition of a species, according to which individuals of one species can mate at will and produce fertile offspring. Apparently, there are barriers to the free interchange of genes even within a species; after all, one out of 50 crosses in this study was not successful. The formation of new species thus needs to be understood as a gradual process, where barriers within a species continually increase, until two groups ca
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| Contact: Natalie Bouaravong press@plos.org 415-568-3445 Public Library of Science Source:Eurekalert |
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