Genetic regulation of cellular morphogenesis in Candida albicans
This work attempts to gain information about the molecular basis of the yeast-to-hypha morphological transition in Candida albicans by investigating the roles of two genes that have been postulated to exert an influence over this process. A C. albicans cDNA had been previously isolated during a screen for cDNAs that encode immunogenic proteins specific to the hyphal form of C. albicans. Sequencing of cDNA10 in this study and database searches indicated that cDNA10 shows a high level of sequence identity to two closely related Saccharomyces cerevisiae ribosomal proteins, Rp10Ap and Rp10Bp. This C. albicans gene was therefore renamed RP10. However, subsequent Northern analysis by Rolf Swoboda showed that the RP10 did not respond to hyphal development per se, but was tightly regulated during growth. It was concluded that RP10 is unlikely to be a regulator of hyphal development in C. albicans. The role of the HST7 MAP kinase kinase was also investigated. An HST7overexpression plasmid was constructed using a novel C. albicans expression vector created in this study, and phenotypic effects of HST7 overexpression in C. albicans and S. cerevisiae were determined. Overexpression of HST7 promoted pseudohyphal growth in a S. cerevisiae diploid strain under conditions of nitrogen starvation, and suppressed the pseudohyphal defects in S. cerevisiae ste 7/ste7 and ste11/ste11 strains. However, HST7 overexpression did not promote constitutive pseudohyphal growth in S. cerevisiae. Overexpression of HST7 suppressed the hyphal defect in a C. albicans hst7/hst7 null mutant, although HST7 overexpressed did not promote constitutive hyphal growth in C. albicans. HST7 is there suggested to be a member of a pathway that is necessary for hyphal growth in C. albicans under some conditions.