Role of Arf GTPases in fungal morphogenesis and virulence.

Hayet Labbaoui,Norma V Solis,Vikram Ghugtyal,Robert A Arkowitz,Scott G Filler,Martine Bassilana,Stéphanie Bogliolo,J Andrew Alspaugh

doi:10.1371/journal.ppat.1006205

Abstract

Virulence of the human fungal pathogen Candida albicans depends on the switch from budding to filamentous growth, which requires sustained membrane traffic and polarized growth. In many organisms, small GTPases of the Arf (ADP-ribosylation factor) family regulate membrane/protein trafficking, yet little is known about their role in fungal filamentous growth. To investigate these GTPases in C. albicans, we generated loss of function mutants in all 3 Arf proteins, Arf1-Arf3, and 2 Arf-like proteins, Arl1 and Arl3. Our results indicate that of these proteins, Arf2 is required for viability and sensitivity to antifungal drugs. Repressible ARF2 expression results in defects in filamentous growth, cell wall integrity and virulence, likely due to alteration of the Golgi. Arl1 is also required for invasive filamentous growth and, although arl1/arl1 cells can initiate hyphal growth, hyphae are substantially shorter than that of the wild-type, due to the inability of this mutant to maintain hyphal growth at a single site. We show that this defect does not result from an alteration of phospholipid distribution and is unlikely to result from the sole Golgin Imh1 mislocalization, as Imh1 is not required for invasive filamentous growth. Rather, our results suggest that the arl1/arl1 hyphal growth defect results from increased secretion in this mutant. Strikingly, the arl1/arl1 mutant is drastically reduced in virulence during oropharyngeal candidiasis. Together, our results highlight the importance of Arl1 and Arf2 as key regulators of hyphal growth and virulence in C. albicans and identify a unique function of Arl1 in secretion.

Highlights

Signal-dependent morphology changes are crucial for the virulence of a range of plant and human fungal pathogens
Sustained membrane traffic is critical for such polarized growth and for the secretion of virulence factors
Since in S. cerevisiae none of these genes is essential for viability [29, 30], we attempted to generate C. albicans strains in which both alleles were deleted

Summary

Introduction

Signal-dependent morphology changes are crucial for the virulence of a range of plant and human fungal pathogens These dramatic cell shape changes require plasma membrane and cell wall targeting of a number of proteins, together with the secretion of extracellular hydrolytic enzymes, critical for pathogenicity [1,2,3]. Small GTPases of the Arf (ADP-ribosylation factor) and Rab (Ras-related in brain) families, which are part of the Ras superfamily, regulate each step of these processes [4,5,6,7,8,9]. While a number of studies in Saccharomyces cerevisiae have shed light on the roles of Arf GTPases, little is known about their role in hyphal growth, a process characteristic of filamentous fungi that is absent in this organism

Methods

Results

Discussion

Conclusion