Just noticed that the JGI has released the Cochliobolus heterostrophus genome sequence at their site predicting 9,633 protein-coding genes. Torrey Mesa Research Institute had access to a sequence many years ago, but it isn’t until now that public version of this genome is available. Cochliobolus is has been a model plant pathogen system and its production of T-Toxin by a PKS gene (Yang et al).
A year ago researchers at James Madison University discovered that, Pedobacter cryoconitis, a bacteria first found on the skin of red backed salamanders, was found to prevent the growth of the chytrid B. dendrobatidis, which is currently decimating frog populations.
(Mountain Yellow-Legged Frog from wikipedia)
The newest research on the subject is being presented this year at ASM by Brianna Lam who worked with other biologists from both San Francisco State University and JMU.
Lam’s research indicates that adding pedobacter to the skin of mountain yellow-legged frogs would lessen the effects of Batrachochytrium dendrobatidis (Bd), a lethal skin pathogen that is threatening remaining populations of the frogs in their native Sierra Nevada habitats.
Lam first conducted petri dish experiments that clearly showed the skin bacteria repelling the deadly fungus. She then tested pedobacter on live infected frogs, bathing some of them in a pedobacter solution. The frogs bathed in pedobacter solution lost less weight than those in a control group of infected frogs that were not inoculated.
In addition to the lab experiments, the JMU and SFSU researchers have studied the yellow-legged frogs in their natural habitats and discovered that some populations with the lethal skin disease survive while others go extinct. The populations that survived had significantly higher proportions of individuals with anti-Bd bacteria. The results strongly suggest that a threshold frequency of individuals need to have anti-Bd bacteria to allow a population to persist with Bd. (from Eureka alert)
The research above is really interesting and I am curious as to how the bacteria is actually killing the chytrid. The only other research I can think of where chytrids were being killed was a BBC news article that wrote about scientists bathing frogs in chloramphenicol.
Spread of wheat rust Puccinia strain Ug99 and consequences on already strained food supplies is discussed in an Op-Ed piece covered in GeneticMaize.
A paper in Science from Jason Crawford and colleagues explores the function of polyketide synthetases (PKS) in the synthesis of the secondary metabolite and carcinogen aflatoxin. Previous work (nicely reviewed in the fungi by Nancy Keller and colleagues) has shown the the PKS genes have several domains. These domains include acyl carrier protein (ACP), transacylase (SAT), ketosynthase (KS), malonyl-CoA:ACP transacylase (MAT), “product template” PT, Aand thioesterase/Claisen cyclase (TE/CLC). These domains make up PksA, but the specific role of each domain’s in synthesis steps has not been fully worked out. Understanding this process and the specificity of the chemical structures that are created can help in redesign of these enzymes for synthesis of new molecules and drugs.
Then authors cloning and combining the domains from a cDNA template of pksA [accession AY371490] (from Aspergillus parasiticus) into various combinations and then evaluated the synthesized products via HPLC. This deconstruction of a complicated protein and its domains is a great example of functionally mapping the role of each part of the enzyme and integrating with the biochemistry of the synthesized products. The findings of this research also mapped a role for the PT product template domain which could suggest where modifications could be made to tweak the synthesized products by these enzymes.
Crawford, J.M., Thomas, P.M., Scheerer, J.R., Vagstad, A.L., Kelleher, N.L., Townsend, C.A. (2008). Deconstruction of Iterative Multidomain Polyketide Synthase Function. Science, 320(5873), 243-246. DOI: 10.1126/science.1154711
Hyphoid logic points out that it is appropriate to discuss about the oomycete Phytophthora infestans on St. Patrick’s Day and mentions a NYT article “The fungus that conquered Europe” that is worth a look.
It is also worth thinking about another blight, well rust, that is spreading through the middle east and could threaten wheat crops worldwide. New Scientist has excellent coverage of Puccinia graminis strain Ug99 which is spreading faster than expected due to a cyclone that spread the rust spores into Iran two years earlier than expected.
What delineates species boundaries in fungi? Much work has been done on biological and phylogenetic species concepts in fungi. Some concepts are reviewed in Taylor et al 2006 and in Taylor et al 2000, and applications can be seen in several pathogens such as Paraccocidiodies, Coccidioides, and the model filamentous (non-pathogenic) fungus Neurospora.
A paper in Fungal Genetics and Biology on species definitions in Cryptococcus neoformans from multi-locus sequencing seeks to provide additional treatment of the observed diversity. A large study of 117 Cryptococcus isolates were examined through multi-locus sequencing (6 loci) and identified two monophyletic lineages within C. neoformans varieties that correspond to var. neoformans and var. grubii. However within the C. gattii samples they identified four monophyletic groups consistent with deep divergences observed from whole genome trees for two strains of C. gattii, MLST, and AFLP studies. By first defining species, we can now test whether any of the species groups have different traits including prevalence in clinical settings and in nature.
BOVERS, M., HAGEN, F., KURAMAE, E., BOEKHOUT, T. (2007). Six monophyletic lineages identified within Cryptococcus neoformans and Cryptococcus gattii by multi-locus sequence typing. Fungal Genetics and Biology DOI: 10.1016/j.fgb.2007.12.004
A review in Plant Cell from Darren Soanes and colleagues summarizes some of the major findings about evolution of phytopathogenic fungi gleaned from genome sequencing highlighting 12 fungi and 2 oomycetes. By mapping evolution of genes identified as virulence factors as well as genes that appear to have similar patterns of diversification, we can hope to derive some principals about how phytopathogenic fungi have evolved from saprophyte ancestors.
They infer from phylogenies we’ve published (Fitzpatrick et al, James et al) that plant pathogenic capabilities have arisen at least 5 times in the fungi and at least 7 times in the eukaryotes. In addition they use data on gene duplication and loss in the ascomycete fungi (Wapinski et al) to infer there large numbers of losses and gains of genes have occurred in fungal lineages.
The Stagonospra nodorum (teleomorph Phaeosphaeria nodorum) genome is now published in Plant Cell, “Sequencing and EST Analysis of the Wheat Pathogen Stagonospora nodorum”. The paper describes the sequencing and analysis of this Dothideomycete fungus. The analyses included identifying genes likely involved in pathogenecity such as PKS and NRPS genes and enabled the discovery of new genes like ToxA.
Robin reviews recent Nature paper by Ilan Wapinski et al describing the orthogroups they built from multiple fungal genomes. I’ve been remiss in reviewing the paper myself, but they’ve created an important resource in the SYNERGY tool for orthology identification and a database of orthologs of some ascomycete fungi. I am excited there is a level of interest in the properties of gene duplication and how this may be an important aspect of adaptation and evolution.
The Cornell Mushroom blog has a nice treatment of the maize pathogen and Mexican delicacy Ustilago maydis corn smut.