Ambient pH signalling in the yeast Yarrowia lipolytica involves YlRim23p/PalC, which interacts with Snf7p/Vps32p, but does not require the long C terminus of YlRim9p/PalI

Abstract

A conserved ambient pH signal transduction pathway has been evidenced in both ascomycetous yeasts and filamentous fungi, called the Rim or Pal pathway, respectively. However, closely related PalC orthologues are found only in Yarrowia lipolytica and in filamentous fungi, where the Rim9p/PalI factor has a much longer C-terminal tail than in other yeasts. We show here that, like Aspergillus nidulans palI mutants, a Ylrim9D mutant has a less extreme phenotype than other mutants of the pathway, whereas rim9 mutants in Saccharomyces cerevisiae and Candida albicans reportedly exhibit a tight Rim phenotype. Deletion of the long C-terminal tail of YlRim9p/ PalI had no phenotypic effect on ambient pH signalling. We also show that the Y. lipolytica PalC orthologue, named YlRim23p, is absolutely required for the alkaline pH response. Its only interactant identified in a genome-wide two-hybrid screen is YlSnf7/Vps32p, confirming the link between the Rim and the Vps pathways. YlRim13p and YlRim20p both interact with YlSnf7/ Vps32p but not with YlRim23p. The long C-terminal tail of YlRim9p/PalI interacts neither with YlRim23p nor with YlSnf7/Vps32p. These results show that YlRim23p is a bona fide component of the Rim pathway in Y. lipolytica and that it participates in the complexes linking pH signalling and endocytosis. INTRODUCTIONExtracellular pH regulation plays major roles in the control of many biological processes, including the survival of fungi and bacteria and the virulence of some of these micro-organisms. Environmental pH profoundly affects gene expression in many organisms, especially in those which are able to grow over a wide pH range. Ambient pH-responsive genes include those encoding permeases, plasma-membrane transporters, secreted proteins and enzymes involved in the synthesis of exported metabolites. In the yeast Yarrowia lipolytica, transcription of the XPR2 and AXP1 genes, encoding alkaline and acidic extracellular proteases, respectively, is tightly controlled by a combination of environmental stimuli, including ambient pH and nutrient availability (Ogrydziak et al., 1977;Ogrydziak, 1993). In Candida albicans, the genes encoding the three proteases Sap4p, Sap5p and Sap6p are under the control of extracellular pH, Sap5p being required for E-cadherin degradation during mucosal tissue invasion (Villar et al., 2007). This pathway has been intensively investigated in Aspergillus nidulans (Penalva & Arst, 2002; Herranz et al., 2005;Hervas-Aguilar et al., 2007; Galindo et al., 2007;Penas et al., 2007;Calcagno-Pizarelli et al., 2007), in Y. lipolytica (Lambert et al., 1997; Tréton et al., 2000;Gonzalez-Lopez et al., 2002;Blanchin-Roland et al., 2005), in several other ascomycetes, including Saccharomyces cerevisiae (Li & Mitchell, 1997;Xu & Mitchell, 2001;Vincent et al., 2003;Xu et al., 2004;Boysen & Mitchell, 2006), in C. albicans (Ramon & Fonzi, 2003;Li et al., 2004;Kullas et al., 2004;Cornet et al., 2005;Barwell et al., 2005;Baek et al., 2006), in the basidiomycete Ustilago maydis (Arechiga-Carvajal & Ruiz-...

Physiological Involvement in pH Signaling of Vps24-mediated Recruitment of Aspergillus PalB Cysteine Protease to ESCRT-III

“…The finding that the arrestin-like PalF, which binds strongly to the PalH 7-TMD receptor cytosolic tail, is ubiquitinated in a PalH-and alkaline ambient pH-dependent manner strongly supports the hypothesis that this connection involves endocytic traffic (27). In the current model, the Bro1 domain-like containing protein PalC, which localizes to cortical structures also in a PalH-and alkaline ambient pH-dependent manner and can bind Vps32 directly, is thought to play a bridging role between the two spatially separated complexes (28,29).…”

Mutational Analysis of Candida albicans SNF7 Reveals Genetically Separable Rim101 and ESCRT Functions and Demonstrates Divergence in bro1-Domain Protein Interactions

“…A third possibility is that the C-terminal group C cluster interacts with an unidentified Rim101 pathway member in C. albicans. In A. nidulans, Yarrowia lipolytica, and S. cerevisiae, an additional Rim101 pathway member, PalC/ Rim23, has been identified which contains a bro1-domain and is able to interact with Snf7 (Tilburn et al 2005;Galindo et al 2007;Blanchin-Roland et al 2008). We identified C. albicans orf19.2914 through a blast search with ScRim23 sequence.…”

The Candida albicans ESCRT Pathway Makes Rim101-Dependent and -Independent Contributions to Pathogenesis

“…Snf7 interacts with Rim20 (9,20), a scaffold protein that binds the Rim101 transcription factor (48), and with Rim13 (8,20), the putative protease responsible for Rim101 proteolytic activation ( Fig. 1) (25).…”