Candida albicans Pma1p Contributes to Growth, pH Homeostasis, and Hyphal Formation.

Hallie S Rane,Esteban L Abeyta,Stella M Bernardo,Samuel A Lee,Jillian E Frye,Summer R Hayek,Karlett J Parra

doi:10.3389/fmicb.2019.01012

Abstract

Candida albicans occupies diverse ecological niches within the host and must tolerate a wide range of environmental pH. The plasma membrane H+-ATPase Pma1p is the major regulator of cytosolic pH in fungi. Pma1p extrudes protons from the cytosol to maintain neutral-to-alkaline pH and is a potential drug target due to its essentiality and fungal specificity. We characterized mutants in which one allele of PMA1 has been deleted and the other truncated by 18–38 amino acids. Increasing C-terminal truncation caused corresponding decreases in plasma membrane ATPase-specific activity and cytosolic pH. Pma1p is regulated by glucose: glucose rapidly activates the ATPase, causing a sharp increase in cytosolic pH. Increasing Pma1p truncation severely impaired this glucose response. Pma1p truncation also altered cation responses, disrupted vacuolar morphology and pH, and reduced filamentation competence. Early studies of cytosolic pH and filamentation have described a rapid, transient alkalinization of the cytosol preceding germ tube formation; Pma1p has been proposed as a regulator of this process. We find Pma1p plays a role in the establishment of cell polarity, and distribution of Pma1p is non-homogenous in emerging hyphae. These findings suggest a role of PMA1 in cytosolic alkalinization and in the specialized form of polarized growth that is filamentation.

Highlights

The opportunistic yeast Candida albicans colonizes an array of ecological niches in the human host, from the oral cavity to the stomach, lower gastrointestinal tract, and the genito-urinary tract, and during infection has the ability to invade the bloodstream and various organs
Previous work has shown that dramatic cytosolic alkalinization precedes hyphal formation in C. albicans; Pma1p has been proposed as a possible mediator of this phenomenon (Stewart et al, 1988)
Overexpression of PMA1 in tetR-PMA1 led to several unexpected phenotypes, including decreased growth compared to wild-type at low pH or in unbuffered media (CSM pH 4, pH 5 and unbuffered CSM) and increased growth at alkaline pH (CSM pH 7.5 or 8.5; data not shown)

Summary

INTRODUCTION

The opportunistic yeast Candida albicans colonizes an array of ecological niches in the human host, from the oral cavity to the stomach, lower gastrointestinal tract, and the genito-urinary tract, and during infection has the ability to invade the bloodstream and various organs. Previous work has shown that dramatic cytosolic alkalinization precedes hyphal formation in C. albicans; Pma1p has been proposed as a possible mediator of this phenomenon (Stewart et al, 1988) This hypothesis has not been confirmed, there is indirect supporting evidence: emerging germ tubes have twice the level of plasma membrane ATPase-specific activity as budding cells, and treatment of cells with proton pump inhibitors blocks both ATPase-specific activity and morphogenesis (Kaur et al, 1988; Stewart et al, 1988, 1989; Monk et al, 1993). C-terminal truncation of the Pma1p protein decreased plasma membrane ATPase-specific activity by 44.1–78.2% We used these partial loss-of-function mutants to assess the role of PMA1 in C. albicans cell biology, hyphal formation, and virulence

MATERIALS AND METHODS

RESULTS

DISCUSSION