The Hyphal Tip: Fungal Genomes and Comparative Genomics

This is a research blog so I though I'd post some quick numbers we are seeing for de novo assembly of the [[Neurospora crassa]] genome using Velvet. The genome of N.crassa is about 40Mb and sequencing of several flow cells using Solexa/Illumina technology to see what kind of de novo reconstruction we'd get.

The genome of Podospora anserina S mat+ strain was sequenced by Genoscope and CNRS and published recently in Genome Biology. The genome sequence data has been available for several years, but it is great to see a publication describing the findings.  The 10X genome assembly with ~10,000 genes provides an important dataset for comparisons

Interesting blog post that mentions N. crassa and RIP

A paper in Current Genetics describes the discovery of Repeat Induced Polymorphism (RIP) in two Euriotiales fungi.  RIP has been extensively studied in Neurospora crassa and has been identified in other Sordariomycete fungi Magnaporthe, Fusiarium. This is not the first Aspergillus species to have RIP described as it was demonstrated in the biotech workhorse Aspergillus oryzae.  However, I think this study is the first to describe RIP in a putatively asexual fungus.  The evidence for RIP is only found in transposon sequences in the Aspergillus and Penicillium.  A really interesting aspect of this discovery is RIP is thought to only occur during sexual stage, but a sexual state has never been observed for these fungi.  

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

Dettman, Anderson, and Kohn recently published a paper in BMC Evolutionary Biology on reproductive experimental evolution in two Neurospora crassa populations evolved under different selective conditions. This is a great study that complements work published last year in Nature on experimental evolution in Saccharomyces cerevisiae populations. Neurospora populations were evolved under high salt and low temperature and were started from either high diversity (interspecific crosses, N. crassa vs N. intermedia) or low diversity (intraspecific cross, two N. crassa isolates D143 (Louisiana, USA)and D69 (Ivory Coast)) as described in Figure 1. The experimentally evolved populations were then tested for asexual and sexual fitness (they were taken through complete meiotic cycle throughout the experiment to avoid insure there was selection on the sexual reproduction pathway.

A quick link to a Neurospora paper in Genetics today entitled "Alternative Splicing Gives Rise to Different Isoforms of the Neurospora crassa Tob55 Protein That Vary in Their Ability to Insert Beta-Barrel Proteins Into the Outer Mitochondrial Membrane". The authors investigated alternative splicing of a gene found in the TOB complex on the outside of the mitochondria.

Several more fungi are on the docket for sequencing at JGI through their community sequencing program. This includes

• The Dothideomycete leaf streak disease causing fungus Mycosphaerella fijiensis
• Soybean rust Phakopsora pachyrhizi
• The Basidiomycete and jelly fungus Tremella mesenterica proposed by Joe Heitman for use as outgroup to the human pathogen Cryptococcus
• The plant pathogen Cochliobolus heterostrophus proposed by Gillian Turgeon which ironically was already sequenced

A exciting research paper "Control of alternative RNA splicing and gene expression by eukaryotic riboswitches" published in Nature details the mechanism of how riboswitches work in Neurospora crassa. While riboswitches have been found and studied in bacteria there has not been extensive work showing how they work in fungi. In bacteria the riboswitch acts as the direct interacting sensor that switches gene

We got word last week from the JGI that our DNA for Neurospora tetrasperma and N. discreta have passed QC and library QC and are on their way to being sequenced. The center also plans to do some EST sequencing to improve gene calling abilities. Why more Neurospora genomes? The sequencing proposal discussed these species as a model system for evolutionary and ecological genetics.