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Repression of chsB expression reveals the functional importance of class IV chitin synthase gene chsD in hyphal growth and conidiation of Aspergillus nidulans

Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan¹

Author for correspondence: Hiroyuki Horiuchi. Tel: +81 3 5841 5170. Fax: +81 3 5841 8015. e-mail: ahhoriu{at}mail.ecc.u-tokyo.ac.jp

The functions of two previously identified chitin synthase genes in Aspergillus nidulans, chsB and chsD, were analysed. First, a conditional chsB mutant was constructed in which the expression of chsB is under the control of a repressible promoter, the alcA promoter, of A. nidulans. Under repressing conditions, the mutant grew slowly and produced highly branched hyphae, supporting the idea that chsB is involved in normal hyphal growth. The involvement of chsB in conidiation was also demonstrated. Next, double mutants of chsB and chsD were constructed, in which chsB was placed under the control of the alcA promoter and chsD was replaced with the argB gene of A. nidulans. These double mutants grew more slowly than the chsB single mutant under high-osmolarity conditions. The hyphae of the double mutant appeared to be more disorganized than those of the chsB single mutant. It was also found that ChsD was functionally implicated in conidiation when the expression of chsB was limited. These results indicate the importance of the ChsD function in the absence of chsB expression. The roles of ChsB and ChsD in hyphal growth and in conidiation were supported by the analysis of the spatial expression patterns of chsB and chsD, using lacZ of Escherichia coli as a reporter gene.

Keywords: cell wall, conidiation, filamentous fungi

Abbreviations: AP, alkaline phosphatase; RACE, rapid amplification of cDNA ends

The GenBank accession number for the the new version of the chsD nucleotide sequence is D83246.

^a These authors contributed equally to this work.

^b Present address: The Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama 351-0198, Japan.

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