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Study: Many lichens are three--not two--symbionts

 
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Chris S.
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Joined: 05 Apr 2009
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Location: Ohio, USA

PostPosted: Tue Jul 26, 2016 9:44 pm    Post subject: Study: Many lichens are three--not two--symbionts Reply with quote

Quite a few members of this forum have, as I do, an interest in lichens. To lichenologists, a newly-published article by Toby Spribille et al, in the journal Science, is big news. The article is behind a paywall, but its abstract, and the summary of a Science editorial by Elizabeth Pennisi, are informative:

First, the editorial summary:
    Lichen isn't much to look at—often just a gray, yellow-green, or garish orange crust on rock or bark. Yet lichens cover up to 6% of Earth's surface, by one estimate. Now, modern genomics is revealing that lichens are startlingly complex. For some 140 years, scientists have understood lichens to be a symbiosis between a fungus, which provides a physical structure and supplies moisture, and a photosynthesizing alga or cyanobacterium, which produces nutrients. Studies of gene activity have now revealed that many lichens are instead a threesome, with two fungi in the mix. The role of the second fungus, a yeast, is uncertain, and some lichen aficionados aren't convinced it is a true symbiotic partner. But others say it's time to throw the textbook understanding of lichens out the window.
Next, the abstract:
    For over 140 years, lichens have been regarded as a symbiosis between a single fungus, usually an ascomycete, and a photosynthesizing partner. Other fungi have long been known to occur as occasional parasites or endophytes, but the one lichen–one fungus paradigm has seldom been questioned. Here we show that many common lichens are composed of the known ascomycete, the photosynthesizing partner, and, unexpectedly, specific basidiomycete yeasts. These yeasts are embedded in the cortex, and their abundance correlates with previously unexplained variations in phenotype. Basidiomycete lineages maintain close associations with specific lichen species over large geographical distances and have been found on six continents. The structurally important lichen cortex, long treated as a zone of differentiated ascomycete cells, appears to consistently contain two unrelated fungi.
Of the above, I find one sentence especially fascinating: "These yeasts[']. . . abundance correlates with previously unexplained variations in phenotype." Wow. So that's it--or part of "it," anyway.

Edit to add: Here is a New York Times article on the work.

--Chris
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Tue Jul 26, 2016 9:51 pm    Post subject: Reply with quote

Definitely interesting stuff!

There's a good layman's level discussion at http://www.theatlantic.com/science/archive/2016/07/how-a-guy-from-a-montana-trailer-park-upturned-150-years-of-biology/491702/ .

--Rik
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Chris S.
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Posts: 2996
Location: Ohio, USA

PostPosted: Tue Jul 26, 2016 10:10 pm    Post subject: Reply with quote

Rik,

Thanks for linking to Ed Yong's excellent piece in The Atlantic. Ed Yong is one of my favorite science writers--he has a genius for making things simple while keeping them right.

--Chris
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