Tag Archives: mating locus

I’ll have the truffles and huitlacoche

Black TruffleA couple of papers should have captured your attention lately in the realm of fungal genomics.

One is the publication of the genome of the black truffle Tuber melanosporum. This appears as an advanced publication at Nature (OA by virtue of Nature’s agreement on genome papers) along with a NYT writeup and is a tasty exploration of the genome of an ascomycete ectomycorrhizal (ECM) fungus. There are several gems in there including the differences in transposable element content, content of gene families related to carbohydrate metabolism. This genome helps open the doorway for exploring the several independent origins of ECM in both ascomycete and basidiomycete fungi.

I’ll also point out there is some work on the analysis of mating type locus found in this genome has applied aspects suggesting that inoculation of roots with both mating types may increase truffle yields in truffle farms. Evidence for sexual reproduction is also discovered from this genome analysis based on the sexual cycle genes present and the structure of the MAT locus.  Much like what was revealed in the genome analysis of the previously ‘asexual’ species Aspergillus fumigatus (and later reconstitution of a sexual cycle), the Tuber genome has the potential for mating and is a heterothallic (outcrossing) fungus based on its mating type locus -just like many other filamentous Ascomycete species.

A second paper I encourage you take a look at (those with a Science subscription) is from Virginia Walbot’s lab on the formation of tumors by U. maydis in Maize. These tumors end up destroying the corn but can produce a delicious (to some) dish that is huitlacooche. The idea that the fungus is co-opting the host system by secreting proteins that acted in the same way as native proteins and that it has a tissue or organ specific repertoire was one that her lab has been pursuing. U. maydis can grow inside corn without detection and  the formation of tumors seems to be a manipulation of the plant as much as it is the pathogen directly taking resources from the plant.  It reminds me a bit of the production of secondary metabolites that can control plant growth like gibberellins produced by fungi.  This kind of manipulation and also ability to evade detection suggests a pretty specific set of controls that prevent the fungus from doing the wrong thing at the wrong time (to avoid detection). So they set out to see if there are a set of organ specific genes that the fungus uses during infection that would suggest a very host-specific strategy by this corn smut.

In this paper the authors evaluate the role of fungal genes specifically expressed in infection of different organs and also the role of secreted proteins in colonization of the organs.  In what is impressive and elegant work, the authors show through the use of microarrays and genetics that there is plant tissue specific gene expression of U. maydis – so infections in leaves express a different set of genes than those in seedlings.  Genetic and phenotypic evaluation of fungal strains with knockouts of sets of the predicted secreted proteins was able to confirm a role for specific secreted proteins that previously may have not had any discernible phenotype. They infect strains with knockouts of sets of genes that encode secreted proteins and compare the virulence when these strains infect individual organs of the maize host.  They showed there is significantly different virulence in the various tissues for a some of the mutants suggesting an organ-specific role for virulence of secreted proteins. They also go on to show that some of this organ specific infection requires organ-specific gene expression by evaluating maize mutants and the ability of the fungus to infect different organs.

Future work will hopefully followup to see what these secreted proteins are manipulating in the host and how they either enable virulence by protecting the pathogen, avoiding detection by turning of host responses, or co-opting host gene networks in some other way.

Martin F, Kohler A, Murat C, Balestrini R, Coutinho PM, Jaillon O, Montanini B, Morin E, Noel B, Percudani R, Porcel B, Rubini A, Amicucci A, Amselem J, Anthouard V, Arcioni S, Artiguenave F, Aury JM, Ballario P, Bolchi A, Brenna A, Brun A, Buée M, Cantarel B, Chevalier G, Couloux A, Da Silva C, Denoeud F, Duplessis S, Ghignone S, Hilselberger B, Iotti M, Marçais B, Mello A, Miranda M, Pacioni G, Quesneville H, Riccioni C, Ruotolo R, Splivallo R, Stocchi V, Tisserant E, Viscomi AR, Zambonelli A, Zampieri E, Henrissat B, Lebrun MH, Paolocci F, Bonfante P, Ottonello S, & Wincker P (2010). Périgord black truffle genome uncovers evolutionary origins and mechanisms of symbiosis. Nature PMID: 20348908

Skibbe DS, Doehlemann G, Fernandes J, & Walbot V (2010). Maize tumors caused by Ustilago maydis require organ-specific genes in host and pathogen. Science (New York, N.Y.), 328 (5974), 89-92 PMID: 20360107

Jelly fungus Tremella genome available at JGI

Tremella mesenterica (from K. Findley)
Tremella mesenterica (from K. Findley)

The Tremella mesenterica genome portal is now live at the JGI. The genome is ~28Mb and the JGI annotation group predicted 8,313 genes, a significantly larger number of peptides predicted for C. neoformans (~7000; 18Mb genome) which may represent new and interesting genes or aspects of gene loss in the Cryptococcus yeast lineage.

Tremella is a Basidiomycete jelly fungus and an interesting study system from the perspective of discovery of novel lignin degrading enzymes.  It also occupies an interesting phylogenetic position being an outgroup to the human pathogenic yeast Cryptococcus neoformans and C. gattii. Comparative genomics on this system may also provide insight into the interesting evolution of the large mating-type locus that was formed through various rearrangements resulting in conversion from a tetrapolar to biopolar mating system.

Tremella may also be an important source of understanding wood degradation and how it differs in jelly fungi from the more distantly related Agaricomycotina (mushroom forming). The fungus is reasonably easy to grow in the laboratory and also to collect from nature. It can handle some desiccation to survive during a dry period only to swell up after  moisture is available.  It is also called Witch’s butter and Tom Volk has a summary of its features on his FOTM page.  It can often be confused with a phylogenetically distinct jelly fungus named Dacyromyces, usually the differences can be best be determined microscopically.  See what kinds of Tremella people have been finding at the Mushroom Observer.

See also

    Sex in fungi: MAT locus cloned from a Zygomycete

    On the cover of this week’s Nature is a picture of Phycomyces blakesleeanus Nature Coverhighlighting the discovery of the MAT locus in this Zygomycete fungus from Alex Idnurm and Joe Heitman and colleagues. While it was previously known that Zygomycetes (the Orange lineage represented by R. oryzae in the tree below) mate, the specific locus has until now, never been discovered. The authors in this study identified the MAT locus through a sequence search looking for HMG-box genes knowing that these are found the Mating Type locus in Basidiomycetes and Ascomycetes. They confirmed the identity through a through set of experiments that included PCR, sequencing and crosses of (+) and (-) strains of P. blakesleeanus, and Southern blots.

    Continue reading Sex in fungi: MAT locus cloned from a Zygomycete