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. Continue reading RIPing in an asexual fungus
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 ÃŸ-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. They found reduced growth rate when a strain expressed only the the longest form of three isoforms and confirmed the protein expression of the three isoforms with mass spec.
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 at the now closed Syngenta Torrey Mesa Research Institute (i.e. this paper on NRPS which used the genome)
- The Sordariale Thielavia terrestris proposed by Novoenzymes presumably for potential in producing novel cellulases as part of biofuel production research.
- The Sordariale and Chestnut blight fungus Cryphonectria parasitica
- EST sequencing for Aspergillus terreus proposed by Scott Baker at PNNL
- Scott is also helping lead a projects to sequence Piromyces and Orpinomyces both early branching Neocallimastigomycota fungi that live in the rumen (which I am probably a little too excited about). Apparently the high A-T content is causing problems in the sequencing phase.
- Agaricus bisporus, sadly the only mushroom some people ever eat (canned and put on pizza or from canned soup), proposed by Mike Challen is also slated to be sequencing in 2008. Did Campell’s already sequence it anyways? We got to see them in their non-native habitat on a field trip in the fall (more pictures!).
- The Basidiomycete EM fungus Paxillus involutus proposed by Anders Tunlid will complement ongoing work in plant-fungal association work.
- Heterobasidion annosu, a basidiomycete fungal pathogen of conifers.
- Three Neurospora genomes proposed by our lab
- The oyster mushroom Pleurotus ostreatus
- The amphibian pathogen Batrachochytrium dendrobatidis that I’m working on with collaborators at Berkeley and the Broad Institute (which sequenced another strain)
- Trichoderma actrovirdi (which doesn’t appear to have any sequence in GenBank) is reportedly in production (bottom of the page).
This complements an ever growing list of fungal genome sequences which is probably topping 80+ now not including the several dozen strains of Saccharomyces that are being sequenced at Sanger Centre and a separately funded NIH project to be sequenced at WashU.
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 expression off through a structural change in the RNA and fit in nicely with the RNA world view.
Using N. crassa, the authors show that alternative splicing is directly regulated through the thiamine metabolism genes which contains previously identified riboswitches. As also highlighted in the accompanying commentary this is also an interesting examples of direct RNA regulation of alternative splicing rather than through peptides like SR proteins.
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. It will allow us and others to test several hypotheses about the molecular evolution of things like genome defense in Neurospora and to understand more about the evolutionary history of the model organism N. crassa.
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.
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.
Here is an image of Neurospora crassa I took today in my first attempt at squashes. These are from strains that Dave Jacobson grew up with his constructs so I can’t take any credit other than playing with the microscope next door. Now my first attempt came out badly, so this is actually Dave’s prep as well. And these got dry so they aren’t as nices as they could be. For much nicer images, see N.B. Raju’s.
All that said, I hope these quick images give a hint at the extremely cool structures these fungi produce. These 8-chain ascospores are the result of meoisis that took place inside the perithecia (which was squeezed gently to release the rosettes [or not too gently in my case]).
( I was previous confused about the sample and had labeled this N. tetrasperma which has 4-chained ascospores [tetra] while this sample is crassa which has 8).