Wednesday March 31

 

Plenary Session II

 

Fungal Way of Living

 

PL2.1

Micro- and macro-colonies of Aspergillus niger are heterogenic with respect to gene expression and secretion

Han A.B. Wosten, Charissa de Bekker, G. Jerre van Veluw, Pauline Krijgsheld, Fengfeng Wang, Robertjan Bleichrodt, Arman Vinck

Microbiology and Kluyver Centre for Genomics of Industrial Fermentations, Utrecht University, The Netherlands

h.a.b.wosten@uu.nl

 

The filamentous fungus Aspergillus niger forms centimeter-scale macro-colonies on solid media, whereas (sub)millimeter micro-colonies are formed within liquid shaken cultures. Previously, it has been shown that zones within macro-colonies of A. niger are heterogenic with respect to gene expression and protein secretion. Recently, we have shown by COPAS technology that gene expression is also heterogenic between micro-colonies of a liquid shaken culture of A. niger. Quantitative PCR on RNA isolated from laser-dissected zones of micro-colonies of A. niger showed that RNA distribution is also heterogenic between zones of these colonies. In fact, using GFP as a reporter it has been shown that even within a particular zone of a macro- or micro-colony gene expression is heterogenic. These data show that a colony of A. niger is not a mass of identical hyphae, not even when such colonies are smaller than 1 millimeter. Our results imply that protein production of A. niger can be improved in industrial fermentations by reducing the heterogeneity within the culture.  

 

 

 

PL2.2

Microtubule-dependent mRNA transport in Ustilago maydis

Michael Feldbrügge1,2, Sebastian Baumann1,2, Janine Koepke1,2, and Thomas Pohlmann1,2

1 Heinrich-Heine University Düsseldorf, Institute for Microbiology, Universitätsstr. 1, 40225 Düsseldorf, Germany, 2 Max-Planck Institute for Terrestrial Microbiology, Department of Organismic Interactions, Karl-von-Frisch-Str., 35039 Marburg, Germany

feldbrue@uni-dusseldorf.de

 

Microtubule-dependent mRNA transport is important for polar growth of infectious filaments in Ustilago maydis. The RNA-binding protein Rrm4 constitutes a key component of this molecular transport system. Combining in vivo UV crosslinking and RNA live imaging revealed that Rrm4 forms an integral part of the mRNP transport machinery and mediates transport of distinct mRNAs. These encode for example polarity factors, protein synthesis factors and mitochondrial proteins. Although a number of potential target mRNAs could be identified, precise molecular function(s) of this transport process remains elusive. In order to uncover the role of Rrm4 during filamentous growth we applied differential proteomics comparing wild type and rrm4 strains. According to our results, Rrm4 is essential for efficient secretion of the bacterial-type chitinase Cts1. Thus, we uncovered a novel molecular link of microtubule-dependent mRNA transport and secretion in fungi.

PL2.3

Membrane traffic in Aspergillus nidulans

Miguel A. Peñalva, Juan F. Abenza, Antonio Galindo, América Hervás-Aguilar and Areti Pantazopoulou

Department of Molecular and Cellular Medicine. Centro de Investigaciones Biológicas CSIC. Ramiro de Maeztu 9, Madrid 28040, Spain

penalva@cib.csic.es

 

In hyphal tip cells of Aspergillus nidulans, intracellular distances between apical and basal regions and between the different nuclei within the same cytoplasm are large. Secretion, which predominates in the apex, is spatially coupled to compensatory endocytosis.

 

The A. nidulans trans- and cis-Golgi is formed by a dynamic network of rings, tubules and fenestrated structures that is strongly polarised. Polarisation of the Golgi appears to be mediated, at least in part, by polarisation of the ERES. Thus, the burning and as yet standing question is what determines polarisation of the transitional ER. The organisation of both the cis- and the trans-Golgi is dramatically but reversibly affected by brefeldin A, possibly acting at two different levels. Brefeldin arrests apical extension but growth is restored after washing out, correlating with recovery of the normal Golgi organisation. One important and unexpected feature of the secretion machinery is that whereas ERES and cis-Golgi elements reach the apical dome, the trans-Golgi seems to be actively excluded from this region. Our data underscore our very poor understanding of the complexities of membrane traffic in filamentous fungi, in spite of its major economic impact in Biotechnology and Medicine.

 

 

 

PL2.4

Sex change in fungi: revealing secrets

Paul S. Dyer

School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK.

Paul.Dyer@Nottingham.ac.uk

 

Fungi are able to reproduce by both sexual and asexual means. The majority of species are able to reproduce sexually, and many species are capable of producing both sexual and asexual spores. However, perhaps 15-20% of all fungi are known only to reproduce by asexual means. Where sexual reproduction occurs some species exhibit ‘heterothallic’ obligate-outbreeding mating systems, whereas others exhibit ‘homothallic’ self-fertile breeding systems. Previous work has suggested that heterothallic sexual reproduction is the ancestral state. A fundamental question in evolutionary biology is therefore what genetic modifications occur to result in ‘sex change’ leading to homothallism and asexuality? Unravelling these changes also has applied significance for potential exploitation of the sexual cycle. Work will be described involving filamentous ascomycete species where a combination of genomic and experimental approaches has been used to investigate the nature of sex change in fungi. Research has focussed in particular on the role of mating-type (MAT) and pheromone-signalling pathway genes in mediating sexuality. In model Aspergillus and Botrytis species it appears that transitions between heterothallism and homothallism can be achieved by a variety of MAT locus rearrangements and other genomic changes, demonstrating the flexible nature of fungal genomes. Meanwhile, some supposedly ‘asexual’ species are revealed to have secretive sexual tendencies – as shown by the recent discovery of a functional sexual cycle in Aspergillus fumigatus (teleomorph Neosartorya fumigata).

 

PL2.5

Unexpected Population Structure in Neurospora crassa from the caribbean basin.

Christopher Ellison, Charles Hall, Angela Kaczmarczyk, David Kowbel, Juliet Welch, Rachel Brem, N. Louise Glass, John W. Taylor

University of California, Berkeley

Taylor.Schoberle@uth.tmc.edu

 

We used solexa sequencing of mRNA to simultaneously identify Single Nucleotide Polymorphisms (SNPs) and quantify gene expression for more than sixty isolates of Neurospora crassa from the Caribbean Basin. Through population genomic analysis of the SNP data, we find strong support for two recently diverged populations, one endemic to Louisiana and the other distributed through Florida, Haiti and the Yucatan. We also identify a subset of genes that show the signature of positive selection and a subset that are differentially expressed between species. Based on the evidence for a recent divergence time and the presence of gene flow between these populations, we argue that this represents an ideal dataset for the study of the early stages of speciation.

 

 

 

 

 

 


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