Endosymbiotic relationshipsin which one organism lives within anotherare striking examples of mutualism, and can often significantly shape the biology of the participant species. In new findings that highlight the extent to which a host organism can become dependent on its internal symbiont, researchers have identified a case in which the reproduction of a fungus has become dependent on bacteria that live within its cytoplasm. The findings, which appear online in the journal Current Biology on April 5th, are reported by Laila Partida and Christian Hertweck from the Leibniz Institute for Natural Product Research and Infection Biology in Jena, Germany.
The particular partnership under study is the symbiosis of the fungus Rhizopus microsporus and Burkholderia bacteria that live within its cells. The two species effectively team up to break down young rice plants for their nutrients, causing a plant disease known as rice seedling blight. Past work from the research group had revealed that the Burkholderia bacteria play a critical role in the virulence of the fungus against rice seedlings: The bacteria produce a plant poison known as rhizoxin, which has been shown to be the causative agent in rice seedling blight.
The researchers now report a second, striking benefit conferred on the fungus by its intracellular symbiont. When the bacteria are eliminated from the fungus with antibiotic treatment, the fungal cells are no longer able to form spores, suggesting that the bacterial symbiont is in fact required for this mode of fungal reproduction. Spore formation in fungi is a universal process that allows the rapid distribution of fungal cells. The new findings appear to represent the first known case in which spore formationalso known as vegetative reproductiondepends on the presence of another organism.
The researchers found that when both organisms were brought together to re-establish the symbiosis, sporulation was restored in the fungus
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Cell Press
5-Apr-2007