A paper in PLoS One, Assessing Performance of Orthology Detection Strategies Applied to Eukaryotic Genomes, reports a new approach to assess the performance of automated orthology detection. These authors also wrote the OrthoMCL (2006 DB paper, 2003 algorithm paper) which uses MCL to build orthologous gene families. The authors discuss the trade-offs between highly
sensitive specific tree-based methods and fast but less sensitive approaches of the Best-Reciprocal-Hits from BLAST or FASTA or some of the hybrid approaches. The authors employ Latent Class Analysis (LCA) to aid in “evaluation and optimization of a comprehensive set of orthology detection methods, providing a guide for selecting methods and appropriate parameters”. LCA is also the statistical basis for feature choice in combing gene predictions into a single set of gene calls in GLEAN written by many of the same authors including Aaron Mackey.
I’ve been reading a lot of orthology and gene tree-species tree reconcilation papers lately, some are listed in Ian Holmes’s group as well as listing some of the software on the BioPerl site. This also follows with on our Phyloinformatics hackathon work which we are trying to formalize in some more documentation for phyloinformatics pipelines to support some of the described use cases. I’m also applying some of this to a tutorial I’m teaching at ISMB2007 this summer.
The New Scientist has an article about the spread of black stem rust caused by Puccinia graminis. We briefly mentioned the 1st release of a Puccinia genome in January. Some more links about the spread of the Ug99 virulent strain.
Continue reading Puccinia black stem rust disease spreading
I’ve never worked with Magnaporthe grisea, the fungus responsible for rice blast, one of the most devastating crop diseases, but I do know that its life cycle is complicated and that knocking out roughly 61% of the genes in the genome and evaluating the mutant phenotype to infer gene function is not trivial. In their recent letter to Nature, Jeon et al did what many of us have dreamed of doing in our fungus of interest: manipulate every gene to find those that contribute to a phenotype of interest.
In their study, the authors looked for pathogenecity genes. Interestingly, the defects in appressorium formation and condiation had the strongest correlation with defects pathogenicity, suggesting that these two developmental stages are crucial for virulence. Ultimately, the authors identify 203 loci involved in pathogenecity, the majority of which have no homologous hits in the sequence databases and have no clear enriched GO functions. Impressively, this constitutes the largest, unbiased list of pathogenecity genes identified for a single species (though so of us, I’m sure, may have a problem with the term “unbiased”).
If you’d like to play with their data, the authors have made it available in their ATMT Database.
Perhaps not a surprise to anyone that has dabbled in evolutionary analysis of proteins, Kawahara and Imanishi (BMC Evolutionary Biology 2007) confirm that not every protein evolves via a molecular clock in Saccharomyces sensu scricto. Using everyone’s favorite evolutionary tool, PAML, the authors identify protein lineages via a whole genome scan that evolve relatively slow or fast compared to the rest of the clade. Some changes even appear to be due to the invisible hand of natural selection and independent of the complications that may have arisen during the whole genome duplication in the ancestor of this clade.
It has been previously speculated that, either upon protein duplication or change in the selective regime of the environment, a protein may rapidly evolve at speciation and then, upon obtaining a new, important function, slow down it’s evolutionary rate to a clock-like tempo. One of the black boxes in this hypothesis is whether or not closely related proteins can rapidly diverge. While the authors are not able to identify a mechanism explaining how, their study demonstrates the plausibility of this hypothesis. However, it remains uncertain if proteins that exhibit rapid divergence will subsequently slow down their evolutionary rate later in time.
It’s good to see evolutionary analysis being applied to fungal genomes. With so many sequenced species spanning a great range of phylogenetic distance, the fungal kingdom is poised to provide great insight into the evolution of eukaryotes.
Kathie Hodge has a nice description with cool photos of a fungus growing in maple syrup. I guess I better make sure our syrup is in the fridge!
I’m including a recapping as many of the talks as I remember. There were 6 concurrent sessions each afternoon so you have to miss a lot of talks. The conference was bursting at the seams as it was- at least 140 people had to be turned away beyond the 750 who attended.
If there was any theme in the conference it was “Hey we are all using these genome sequences we’ve been talking about getting”. I only found the overview talks that solely describe the genome solely a little dry as compared to those more focused on particular questions. I guess my genome palate is becoming refined.
Continue reading Fungal Genetics 2007 details
A Fungal Genetics 2007 summary.
Wow. What a meeting! I am still exhausted and not just because of the very late Saturday night dancing at the close of the conference. I will just say anyone who thinks scientists are boring people should witness the passion researchers have for their science and in sharing it with other people. Not to mention that some know how to put on their dancing shoes and let loose. Because of the atmosphere at the Asilomar conference center, it really did feel like I was at a super fun science camp that culminated with a rock band and dancing in the big hall.
I am also digesting the science from the talks and social interactions with a variety of people enthusiastic about mycology, genomes, and evolution (which could be a conference unto itsself). There were presentations on a lot of really great topics, from symbiosis between mycorhizal fungi and plants (Laccaria bicolor) to cell wall structure in Cryptococcus. I got to meet so many people who are making an impact in the fungal community both in their research and in the resources provide online. I will try and re-cap so I can remember everything I saw.
Continue reading Fungal Genetics 2007 summary
Self and non-self recognition is important for fungi when hyphae interact fuse if they should compartmentalize and undergo apoptosis to kill the heterokaryoton or exchange nutrients. This process is part of cell defense and to limit to the movement of mycoviruses.
A paper in PLOS ONE describes the Genesis of Fungal Non-Self Repertoire. This kind of work goes on down the hall from us as well in the Glass lab among others. This recent paper describes het genes, which contain WD40 repeats and different combinations of these help control specificity. There is of course a diverse literature on this subject especially in Neurospora, and I’m not reviewing it here, but it is an imporant process in understanding how fungi interact with their environment.
We’re at Asilomar mtg for Fungal Genetics 2007. We’ll try and blog a bit about the interesting talks and data.Â I’m curious how many fungal geneticists are in fact reading blogs like these and if this medium will work for idea dissemination.
The Candida clade of Hemiascomycete fungi have received much attention from funding bodies so that many genomic and experimental resources are available address questions of pathogenecity and industrial applications of these species.
The Candida genus
Traditionally, species of yeasts that were thought to be asexual were given the genus name Candida. This has lead to Candida being a sort of taxonomic rubbish bin as this system of classification breaks down when asexuality arises more than once (creating homoplasy). For example, the asexual Candida glabrata is found within the Saccharomyces clade when molecular phylogenetics is applied. The problem lies in that many of these species appear very similar visually and microscopically and so there had not been enough phylogenetically informative phenotypic characters to easily classify them further. With the use of molecular phylogenetics the classifications have been improved as shown in several studies, however we retain the historical nature of the genus and species names for these organisms for the time being even though the phylogenetic diversity of species in the “genus” is much broader than other genus-level classifications. It will be interesting to see whether taxonomic proposals like PhyloCode or traditional revisions of the species names will provide new names for the group.
The Candida Genome Database (CGD) sister to the Saccharomyces Genome Database (SGD) provides resources for phenotype and sequences related to human commensal and dimorphic fungus Candida albicans. A recent paper by Arnaud et al describes the resources that are available through their website. An essentially completed C. albicans diploid genome with curated gene models and annotations provides an essential resource for this model pathogenic system. In addition to the SC5314 strain of C. albicans the white-opaque (WO) strain can switch between different colony morphologies – white and smooth or gray and rod shaped.
6 additional species have had their genomes in the Candida clade have had their genomes sequenced including Pichia stipis, Debaryomyces hansenii, Candida lusitaniae, Candida tropicalis, Candida guilliermondii, and Lodderomyces elongisporus. These resources will hopefully shed some light on the importance and mechanisms for dimorphic switching in the pathogen C. albicans, the importance and evolution of alternative codon usage in the clade, and better usage of the industrial yeasts like P. stipitis and D. hansenii.