Calcium Transport Proteins in Fungi: The Phylogenetic Diversity of Their Relevance for Growth, Virulence, and Stress Resistance

Abstract

The key players of calcium (Ca²⁺) homeostasis and Ca²⁺ signal generation, which are Ca²⁺ channels, Ca²⁺/H⁺ antiporters, and Ca²⁺-ATPases, are present in all fungi. Their coordinated action maintains a low Ca²⁺ baseline, allows a fast increase in free Ca²⁺ concentration upon a stimulus, and terminates this Ca²⁺ elevation by an exponential decrease - hence forming a Ca²⁺ signal. In this respect, the Ca²⁺ signaling machinery is conserved in different fungi. However, does the similarity of the genetic inventory that shapes the Ca²⁺ peak imply that if "you've seen one, you've seen them all" in terms of physiological relevance? Individual studies have focused mostly on a single species, and mechanisms elucidated in few model organisms are usually extrapolated to other species. This mini-review focuses on the physiological relevance of the machinery that maintains Ca²⁺ homeostasis for growth, virulence, and stress responses. It reveals common and divergent functions of homologous proteins in different fungal species. In conclusion, for the physiological role of these Ca²⁺ transport proteins, "seen one," in many cases, does not mean: "seen them all."

Keywords: calcium channel; calcium proton antiporter; calcium pump; calcium signal; calcium signaling; filamentous fungi; yeast.

FIGURE 1

Subcellular localization of Ca²⁺ channels, Ca²⁺/H⁺ exchangers, and Ca²⁺ ATPases in the model yeast S. cerevisiae (A) and other fungi (B). Homologs are depicted in identical colors. Subcellular localizations are shown as described or assumed in the literature. Data from fungi other than S. cerevisiae are depicted in a simplified model of a fungal hypha as most of these data were gained from filamentous fungi. Note the more complex localization patterns and larger number of protein family members in non-yeast fungi.