title: Cytosolic free calcium dynamics as related to hyphal and colony growth in the filamentous fungal pathogen Colletotrichum graminicola.
abstract: Tip growth of pollen tubes and root hairs of plants is oscillatory and orchestrated by tip-focussed variations of cytosolic free calcium ([Ca(2+)]cyt). Hyphae of filamentous fungi are also tubular tip-growing cells, and components of the Ca(2+) signalling machinery, such as Ca(2+) channels and Ca(2+) sensors, are known to be important for fungal growth. In this study, we addressed the questions if tip-focussed [Ca(2+)]cyt transients govern hyphal and whole-colony growth in the maize pathogen Colletotrichum graminicola, and whether colony-wide [Ca(2+)]cyt dynamics rely on external Ca(2+) or internal Ca(2+) stores. Ratiometric fluorescence microscopy of individual hyphae expressing the Ca(2+) reporter Yellow Cameleon 3.6 revealed that Ca(2+) spikes in hyphal tips precede the re-initiation of growth after wounding. Tip-focussed [Ca(2+)]cyt spikes were also observed in undisturbed growing hyphae. They occurred not regularly and at a higher rate in hyphae growing at a medium-glass interface than in those growing on an agar surface. Hyphal tip growth was non-pulsatile, and growth speed was not correlated with the rate of spike occurrence. A possible relationship of [Ca(2+)]cyt spike generation and growth of whole colonies was assessed by using a codon-optimized version of the luminescent Ca(2+) reporter Aequorin. Depletion of extracellular free Ca(2+) abolished [Ca(2+)]cyt spikes nearly completely, but had only a modest effect on colony growth. In a pharmacological survey, some inhibitors targeting Ca(2+) influx or release from internal stores repressed growth strongly. However, although some of those inhibitors also affected [Ca(2+)]cyt spike generation, the effects on both parameters were not correlated. Collectively, the results indicate that tip growth of C. graminicola is non-pulsatile and not mechanistically linked to tip-focused or global [Ca(2+)]cyt spikes, which are likely a response to micro-environmental parameters, such as the physical properties of the growth surface.
authors.affiliation: Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences (IAEW), Faculty of Natural Sciences III, Martin Luther University Halle-Wittenberg, 06099 Halle (Saale), Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Lange
authors.affiliation: Plant Nutrition Laboratory, Institute of Agricultural and Nutritional Sciences (IAEW), Faculty of Natural Sciences III, Martin Luther University Halle-Wittenberg, 06099 Halle (Saale), Germany. Electronic address: edgar.peiter@landw.uni-halle.de.
authors.forename: Edgar
authors.initials: E
authors.lastname: Peiter
mesh_terms: D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000235:genetics; D002147:Calmodulin / Q000235:genetics; D060833:Cellular Microenvironment / Q000235:genetics; D020231:Colletotrichum / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D003600:Cytosol / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D025301:Hyphae / Q000235:genetics* / Q000254:growth & development; D008164:Luminescent Proteins / Q000235:genetics; D008856:Microscopy, Fluorescence; D011993:Recombinant Fusion Proteins / Q000235:genetics
chemical_list: D002147:Calmodulin; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; C579281:YCaM3.6 protein; D002118:Calcium
keywords: Aequorin luminometry; Calcium signalling; Colletotrichum graminicola; Hyphal tip growth; Yellow cameleon imaging