Abstract
Although the analysis of genetic interactions and networks is a powerful approach to understanding biology, it has not been applied widely to the pathogenic yeast Candida albicans Here, we describe the use of both screening and directed genetic interaction studies based on complex haploinsufficiency to probe the function of the R: egulation of A: ce2 and M: orphogenesis (RAM) pathway in C. albicans A library of 5200 Tn7-mutagenized derivatives of a parental strain heterozygous at CBK1, the key kinase in the RAM pathway, was screened for alterations in serum-induced filamentation. Following confirmation of phenotypes and identification of insertion sites by sequencing, a set of 36 unique double heterozygous strains showing complex haploinsufficiency was obtained. In addition to a large set of genes regulated by the RAM transcription factor Ace2, genes related to cell wall biosynthesis, cell cycle, polarity, oxidative stress, and nitrogen utilization were identified. Follow-up analysis led to the first demonstration that the RAM pathway is required for oxidative stress tolerance in a manner related to the two-component-regulated kinase Chk1 and revealed a potential direct connection between the RAM pathway and the essential Mps1 spindle pole-related kinase. In addition, genetic interactions with CDC42-related genes MSB1, a putative scaffold protein, and RGD3, a putative Rho GTPase-activating protein (GAP) were identified. We also provide evidence that Rgd3 is a GAP for Cdc42 and show that its localization and phosphorylation are dependent on Cbk1.