Roles of three Fusarium oxysporum calcium ion (Ca2+) channels in generating Ca2+ signatures and controlling growth

Abstract

Spatial and temporal changes of cytoplasmic calcium ions ([Ca2+]c), caused by external stimuli, are known as the Ca2+ signature and presumably control cellular and developmental responses. Multiple types of ion channels, pumps, and transporters on plasma and organellar membranes modulate influx and efflux of Ca2+ to and from the extracellular environment and internal Ca2+ stores to form Ca2+ signatures. Expression of a fluorescent protein-based Ca2+ probe, Cameleon YC3.60, in Fusarium oxysporum enabled us to study how disruption of three Ca2+ channel genes, including FoCCH1, FoMID1 and FoYVC1, affects Ca2+ signature formation at polarized hyphal tips and whether specific changes in the Ca2+ signature caused by these mutations are related to growth-related phenotypes. Resulting mutants displayed altered amplitude, interval, and duration of Ca2+ pulses under various external Ca2+ concentrations as well as changes in sporulation and growth. Loss of FoMID1 and FoCCH1, genes encoding putative plasma membrane channel proteins, had a major impact on Ca2+ signatures and growth, while disruption of FoYVC1, which encodes a vacuolar channel, only subtly affected both traits. Results from our study provide new insights into the underpinning of Ca2+ signaling in fungi and its role in controlling growth and also raise several new questions.