The Mep2p ammonium permease controls nitrogen starvation-induced filamentous growth in Candida albicans

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Candida albicans is a major human fungal pathogen.
• Nitrogen availability is a key environmental signal regulating C. albicans morphology.
• Switching to filamentous growth is crucial for C. albicans virulence.

Purpose of the Study:

• To elucidate the dual role of Mep2p in nitrogen uptake and filamentous growth induction in C. albicans.
• To investigate the signaling pathways regulated by Mep2p under different nitrogen conditions.
• To understand the regulatory circuit controlling morphogenesis in response to ammonium availability.

Main Methods:

• Gene expression analysis of MEP1 and MEP2 under nitrogen starvation.
• Functional characterization of Mep2p in ammonium transport and signaling.
• Investigation of Mep2p's interaction with MAP kinase and cAMP signaling pathways.
• Mutational analysis of Mep2p's C-terminal tail.

Main Results:

• Mep2p, an ammonium permease, is essential for inducing filamentous growth under nitrogen-limiting conditions.
• Mep2p activates Ras1p-dependent signaling pathways (MAP kinase and cAMP) via its C-terminal tail, independent of transport.
• Under ammonium-replete conditions, Mep2p primarily functions in transport, and signaling is suppressed, favoring yeast growth.
• Mep2p is a less efficient transporter but highly expressed, crucial for its signaling role.
• High ammonium concentrations repress filamentous growth, even when signaling pathways are artificially activated.

Conclusions:

• Mep2p plays a critical dual role in C. albicans: facilitating ammonium uptake and mediating filamentous growth induction.
• A regulatory circuit exists where ammonium, the preferred nitrogen source, also inhibits morphogenesis via Mep2p.
• Understanding this mechanism provides insights into controlling C. albicans pathogenesis.