FigA, a Putative Homolog of Low-Affinity Calcium System Member Fig1 in Saccharomyces cerevisiae, Is Involved in Growth and Asexual and Sexual Development in Aspergillus nidulans

Abstract

ABSTRACTCalcium-mediated signaling pathways are widely employed in eukaryotes and are implicated in the regulation of diverse biological processes. InSaccharomyces cerevisiae, at least two different calcium uptake systems have been identified: the high-affinity calcium influx system (HACS) and the low-affinity calcium influx system (LACS). Compared to the HACS, the LACS in fungi is not well known. In this study, FigA, a homolog of the LACS member Fig1 fromS. cerevisiae, was functionally characterized in the filamentous fungusAspergillus nidulans. Loss offigAresulted in retardant hyphal growth and a sharp reduction of conidial production. Most importantly, FigA is essential for the homothallic mating (self-fertilization) process; further, FigA is required for heterothallic mating (outcrossing) in the absence of HACSmidA. Interestingly, in afigAdeletion mutant, adding extracellular Ca2+rescued the hyphal growth defects but could not restore asexual and sexual reproduction. Furthermore, quantitative PCR results revealed thatfigAdeletion sharply decreased the expression ofbrlAandnsdD, which are known as key regulators during asexual and sexual development, respectively. In addition, green fluorescent protein (GFP) tagging at the C terminus of FigA (FigA::GFP) showed that FigA localized to the center of the septum in mature hyphal cells, to the location between vesicles and metulae, and between the junctions of metulae and phialides in conidiophores. Thus, our findings suggest that FigA, apart from being a member of a calcium uptake system inA. nidulans, may play multiple unexplored roles during hyphal growth and asexual and sexual development.