CDKs and the yeast-hyphal decision

Fungal cells exist in a diverse range of morphologies. Some species, such as Candida albicans, are dimorphic capable of growing either in a yeast-like form or as a hypha. Cyclin-dependent kinases (CDKs) have long been thought to play a central role in the yeast-hyphal decision. However, until recently direct links of CDKs with proteins that execute polarized growth were elusive. In this review I will focus on new findings that have established concrete links between CDKs and several key components of the polarity machinery in C. albicans and the budding yeast Saccharomyces cerevisiae. Inhibitory phosphorylation of the GTPase-activating proteins (GAPs) of Cdc42 has emerged as a common mechanism underlying polarized growth in both organisms. C. albicans contains a hyphal-specific cyclin Hgc1. In association with the CDK Cdc28 it ensures hyphal development by phosphorylating the Cdc42 GAP Rga2, two septins and the transcription factor Efg1. This review will discuss both conserved mechanisms and ones specific for hyphal development in C. albicans.