The role of microtubule-dependent mRNA transport during polar growth of Ustilago maydis
Final Report Abstract
Ustilago maydis is a basidiomycete that infects corn causing smut disease. Prerequisite for pathogenicity is the formation of an infectious filament that exhibits unipolar growth. An important regulator of this process is the RNA-binding protein Rrm4 that functions as integral part of the microtubule-dependent mRNA transport machinery. In vivo UV crosslinking experiments revealed that Rrm4 binds distinct mRNAs encoding, for example, polarity factors such as the small G protein Rho3 or the septin Cdc3. Importantly the encoded proteins exhibited distinct subcellular localisation at the growth cone or at retraction septa. The aim of this proposal was the investigation of the functional role of microtubule-dependent shuttling of mRNPs during accumulation of polarity factors. To reach this goal we proposed to study the subcellular localisation of mRNAs, the local translation and the accumulation of the encoded protein. Moreover, we investigated the role of this transport process during unipolar growth. Studying the septin Cdc3 as a prime example revealed that loss of cdc3 causes defects in unipolar growth that resemble defects observed in rrm4∆ filaments. Using an improved RNA live imaging method allowed the study of endogenously expressed cdc3 mRNA. We discovered that cdc3 mRNA localised to Rrm4-positive endosomes and that the mRNA did not accumulate at the poles. Intriguingly, the endcoded septin protein Cdc3 also accumulated at the same endosomes suggesting endosome-coupled translation. Consistently, the presence of cdc3 mRNA was prerequisite for the presence of protein, and ribosomal proteins of both subunits co-localise with shuttling endosomes in the presence of mRNA. Studying the dynamic assembly of Cdc3 in septin filaments at the hyphal growth cone revealed that endosomal transport is important for efficient formation of septin filaments. Thus, microtubule-dependent transport of septin mRNA and protein mediated by shuttling endosomes is crucial for assembly of septin filaments at the growth cone.
Publications
- (2009) The fungal RNA-binding protein Rrm4 mediates long-distance transport of ubi1 and rho3 mRNAs. EMBO J. 28: 1855-1866
J. König, S. Baumann, J. Koepke, T. Pohlmann, K. Zarnack and M. Feldbrügge
- (2010) Posttranscriptional control of growth and development in Ustilago maydis. Curr. Opin. Microbiol. 13: 693-699
E. Vollmeister and M. Feldbrügge
- (2011) The RNA-binding protein Rrm4 is essential for efficient secretion of endochitinase Cts1. Mol. Cell. Proteom. M111.011213-1-15
J. Koepke, F. Kaffarnik, C. Haag, K. Zarnack, N.M. Luscombe, J. König, J. Ule, R. Kellner, D. Begerow and M. Feldbrügge
- (2012) Fungal development of the plant pathogen Ustilago maydis. FEMS Microbiol. Rev. 36: 59-77
E. Vollmeister, K. Schipper, S. Baumann, C. Haag, T. Pohlmann, J. Stock and M. Feldbrügge
(See online at https://doi.org/10.1111/j.1574-6976.2011.00296.x) - (2012) Kinesin-3 and dynein mediate microtubule-dependent co-transport of mRNPs and endosomes. J. Cell Sci. 125: 2740-2752
S. Baumann, T. Pohlmann, M. Jungbluth, A. Brachmann and M. Feldbrügge
(See online at https://doi.org/10.1242/jcs.101212)
