Gpa2, a G-protein alpha subunit required for hyphal development in Candida albicans.

Candida albicans is able to respond to environmental changes by inducing a distinct morphological program, which is related to the ability to infect mammalian hosts. Although some of the signal transduction pathways involved in this response are known, it is not clear how the environmental signals are sensed and transmitted to these transduction cascades. In this work, we have studied the function of GPA2, a new gene from C. albicans, which encodes a G-protein alpha-subunit homologue. We demonstrate that Gpa2 plays an important role in the yeast-hypha dimorphic transition in the response of C. albicans to some environmental inducers. Deletion of both alleles of the GPA2 gene causes in vitro defects in morphological transitions in Spider medium and SLAD medium and in embedded conditions but not in medium containing serum. These defects cannot be reversed by exogenous addition of cyclic AMP. However, overexpression of HST7, which encodes a component of the filament-inducing mitogen-activated protein kinase (MAPK) cascade, bypasses the Gpa2 requirement. We have obtained different gain-of-function and loss-of-function mutant alleles of the GPA2 gene, which we have introduced in several C. albicans genetic backgrounds. Our results indicate that, in response to environmental cues, Gpa2 is required for the regulation of a MAPK signaling pathway.