A G1 Cyclin Is Necessary for Maintenance of Filamentous Growth in Candida albicans

Candida albicans undergoes a dramatic morphological transition in response to various growth conditions. This ability to switch from a yeast form to a hyphal form is required for its pathogenicity. The intractability ofCandida to traditional genetic approaches has hampered the study of the molecular mechanism governing this developmental switch. Our approach is to use the more genetically tractable yeastSaccharomyces cerevisiae to yield clues about the molecular control of filamentation for further studies inCandida . G1 cyclins Cln1 and Cln2 have been implicated in the control of morphogenesis inS. cerevisiae . We show thatC. albicans CLN1 (CaCLN1 ) has the same cell cycle-specific expression pattern asCLN1 andCLN2 ofS. cerevisiae . To investigate whether G1 cyclins are similarly involved in the regulation of cell morphogenesis during the yeast-to-hypha transition ofC. albicans , we mutatedCaCLN1 .Cacln1/Cacln1 cells were found to be slower than wild-type cells in cell cycle progression. TheCacln1/Cacln1 mutants were also defective in hyphal colony formation on several solid media. Furthermore, while mutant strains developed germ tubes under several hypha-inducing conditions, they were unable to maintain the hyphal growth mode in a synthetic hypha-inducing liquid medium and were deficient in the expression of hypha-specific genes in this medium. Our results suggest that CaCln1 may coordinately regulate hyphal development with signal transduction pathways in response to various environmental cues.