THE CHSD AND CHSE GENES OF ASPERGILLUS-NIDULANS AND THEIR ROLES IN CHITIN SYNTHESIS

Specht, C. A., Liu, Y., Robbins, P. W., Bulawa, C. E., lartchouk, N., Winter, K. R., Riggle, P. J., Rhodes, J. C., Dodge, C. L., Culp, D. W. , and Borgia, P. T. 1996, The chsD and chsE genes of Aspergillus nidul ans and their roles in chitin synthesis, Fungal Genetics and Biology 2 0, 153-167. Two chitin synthase genes, chsD and chsE, were identified from the filamentous ascomycete Aspergillus nidulans. In a region that is conserved among chitin synthases, the deduced amino acid sequences of chsD and chsE have greater sequence identity to the polypeptides e ncoded by the Saccharomyces cerevisiae CHS3 gene (also named CSD2, CAL 1, DIT101, and KTI1) and the Candida albicans CHS3 gene than to other chitin synthases. chsE is more closely related to the CHS3 genes, and this group constitutes the class IV chitin synthases, chsD differs suf ficiently from the other classes of fungal chitin synthase genes to co nstitute a new class, class V. Each of the wild-type A, nidulans genes was replaced by a copy that had a substantial fraction of its coding region replaced by the A. nidulans argB gene, Hyphae from both chsD an d chsE disruptants contain about 60-70% of the chitin content of wild- type hyphae, The morphology and development of chsE disruptants are in distinguishable from those of wild type, Nearly all of the conidia of chsD disruption strains swell excessively and lyse when germinated in low osmotic strength medium. Conidia that do not lyse produce hyphae t hat initially have normal morphology but subsequently lyse at subapica l locations and show ballooned walls along their length. The lysis of germinating conidia and hyphae of chsD disruptants is prevented by the presence of osmotic stabilizers in the medium. Conidiophore vesicles from chsD disruption strains frequently swell excessively and lyse, re sulting in colonies that show reduced conidiation. These properties in dicate that chitin synthesized by the chsD-encoded isozyme contributes to the rigidity of the walls of germinating conidia, of the subapical region of hyphae, and of conidiophore vesicles, but is not necessary for normal morphology of these cells, The phenotypes of chsD and chsE disruptants indicate that the chitin synthesized by each isozyme serve s a distinct function, The propensity of a chsD disruptant for osmotic ally induced lysis was compared to that of strains carrying two other mutations (tsE6 and orlA::trpC) which also result in reduced chitin co ntent and vegetative cell lysis. The concentration of osmotic stabiliz er necessary to remedy the lysis of strains carrying the three mutatio ns is inversely related to the chitin content of each strain, This fin ding directly demonstrates the importance of chitin to the integrity o f the cell wall and indicates that agents that inhibit the chsD-encode d chitin synthase could be useful anti-Aspergillus drugs. (C) 1996 Aca demic Press, Inc.