Abstract

Biofilms are a major source of pathogenicity in Candida albicans and are connected to about half the deaths due to systemic candidiasis. Biofilm formation is controlled by a transcriptional network and involves over a thousand genes including a small gene we have named PPP1 (Punctate Pattern Protein 1). This is a biofilm-upregulated gene encoding an unexamined protein found only in Candida albicans and its sister species Candida dubliniensis. In this study, we characterize this protein by analysing its effect on biofilm formation and its cellular localization. We focus on fluorescent microscopy to identify its subcellular localization and links to other cellular processes. First, we tagged Ppp1 with the green fluorescent protein (GFP) and imaged the protein expression pattern. This expression pattern was used to identify subcellular compartments with similar patterns and direct knockouts and tags of proteins defining these domains. Next, we screened the mutant and complement strain through stress and invasive assays and confocal microscopy to identify a distinct phenotype. Disruptions and tagging of Sur7 defining the eisosome and Arc35 defining the actin cytoskeleton suggested that Ppp1 was not a component of either the eisosome or actin cytoskeleton. However, tagging Sed5, a Golgi defining protein, identified colocalization between the puncta. Since there is no clear distinction between Golgi compartment proteins and secretory proteins, we tagged and analyzed Sap2 and compared data with results for Ppp1. We also tagged Orf19.6274 and Orf19.4654, proteins with similar characteristics to Ppp1 and compared their patterns to Ppp1 puncta. These experiments support a model that Ppp1 is localized in the Golgi.