31 Functional Dissection of the Chitin Synthase System for the Growth and Morphogenesis of Aspergillus nidulans

Hiroyuki Horiuchi

Author address: 

Department of Biotechnology The University of Tokyo 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

Abstract: 

Chitin is one of the major cell wall components in most filamentous fungi.Chitin synthases catalyze the polymerization of N-acetyl-D - glucosamine (GlcNAc) using UDP-GlcNAc as a substrate. Recent analyses of genome sequences in many filamentous fungi demonstrate that there are several genes that encode chitin synthases (chs genes) in each fungus. Aspergillus nidulans is ascomycete filamentous fungus and is used as one of the model organism in many filamentous fungi. We have cloned six chs genes from A. nidulans and analyzed their roles in hyphal tip growth and morphogenesis (reviewed in references 1 and 2). These are, chsA, chsB, chsC, chsD, csmA, and csmB, and their gene products belong to classes II, III, I, IV, V, and VI, respectively. chsB-deletion mutants formed very small colonies with many hyphal branches, suggesting that chsB plays an important role in hyphal tip growth. Deletions of chsC and/or chsD did not cause any defects. Deletion of chsA caused slight reduction of conidiation efficiency. In contrast, chsA and chsC double deletion mutants showed pleiotropic defects in asexual and sexual developments and growth sensitivity to various reagents. These results suggest that chsA and chsC have overlapping functions in these processes. csmA and csmB encode the proteins consisting of a myosin-motor like domain at their N-termini and a chitin synthase domain at their C-termini. csmA deletion mutants showed growth sensitivity to hypo-osmotic stress and formed swollen hyphae and intrahyphal hyphae. These phenotypic defects were also observed in csmB deletion mutants. Deletions of both csmA and csmB caused synthetic lethality. Overexpression of csmA could not suppress the defects of the csmB deletion mutant and overexpression of csmB could not suppress those of the csmA deletion mutant. These results suggest that although csmA and csmB have some overlapping functions, they have different functions in hyphal growth. The localizations of chs gene products were investigated by using epitopetagged chitin synthases. HA-ChsA mainly localized at forming septa, while FLAG-ChsB, FLAG-ChsC, CsmA-HA, and CsmB-FLAG localized primarily at hyphal tips and forming septa. To investigate the movement of chitin synthase in living hyphae, we analyzed it using EGFP-ChsB and found that it moved from the outer rim to the center of septation sites during septum development. These results suggest that chitin synthesis in hyphal growth and septum formation is a complex process and several chitin synthases function in it References 1) Ichinomiya, M., Ohta, A., and Horiuchi, H. (2005). Curr. Genet. 48: 171- 183. 2) Takeshita, N., Yamashita, S., Ohta, A., and Horiuchi, H. (2006). Mol. Microbiol. 59:1380-1394.
2007

abstract No: 

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Full conference title: 

The First International Fungal / Plant Cell Wall Meeting
    • International Fungal / Plant Cell Wall Meeting 1st