Ca2+ Signalling Differentially Regulates Germ-Tube Formation and Cell Fusion in Fusarium oxysporum

Abstract

Fusarium oxysporum is an important plant pathogen and an emerging opportunistic human pathogen. Germination of conidial spores and their fusion via conidial anastomosis tubes (CATs) are significant events during colony establishment in culture and on host plants and, hence, very likely on human epithelia. CAT fusion exhibited by conidial germlings of Fusarium species has been postulated to facilitate mitotic recombination, leading to heterokaryon formation and strains with varied genotypes and potentially increased virulence. Ca2+ signalling is key to many of the important physiological processes in filamentous fungi. Here, we tested pharmacological agents with defined modes of action in modulation of the mammalian Ca2+ signalling machinery for their effect on germination and CAT-mediated cell fusion in F. oxysporum. We found various drug-specific and dose-dependent effects. Inhibition of calcineurin by FK506 or cyclosporin A, as well as chelation of extracellular Ca2+ by BAPTA, exclusively inhibit CAT induction but not germ-tube formation. On the other hand, inhibition of Ca2+ channels by verapamil, calmodulin inhibition by calmidazolium, and inhibition of mitochondrial calcium uniporters by RU360 inhibited both CAT induction and germ-tube formation. Thapsigargin, an inhibitor of mammalian sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), partially inhibited CAT induction but had no effect on germ-tube formation. These results provide initial evidence for morphologically defining roles of Ca2+-signalling components in the early developmental stages of F. oxysporum colony establishment—most notably, the indication that calcium ions act as self-signalling molecules in this process. Our findings contribute an important first step towards the identification of Ca2+ inhibitors with fungas-specific effects that could be exploited for the treatment of infected plants and humans.

Synchronization of oscillatory growth prepares fungal hyphae for fusion

“…mCherry-ChsB still localized at hyphal tips, however, no obvious oscillating dynamic recruitment was observed ( Figure 4f ). mCherry-ChsB localized directly to the plasma membrane at the tip, without prior accumulation at the Spitzenkörper, confirming with previous reports the importance of Ca 2+ for well-regulated pulsatile secretion ( Kurian et al, 2022 ). The localization of GFP-SofT to hyphal tips was abolished after the addition of 5 mM EGTA, indicating Ca 2+ -dependent recruitment to the plasma membrane ( Figure 4g ).…”

Looking outside the box: a comparative cross-kingdom view on the cell biology of the three major lineages of eukaryotic multicellular life

“…For instance, intracellular pulsed Ca 2+ signaling coordinates actin assembly and targeted exocytosis during hyphal tip growth [ 201 ] (see Sect. “ Tip growth ”), whereas extracellular Ca 2+ pulses are involved in the cell-to-cell communication during germling fusion [ 109 , 149 ].…”

Plant-Pathogenic Fusarium Species

“…In the present Special Issue entitled “Plant-Pathogenic Fusarium Species“ ten research articles have been published concerning pathogens from the Fusarium oxysporum species complex (FOSC) [ 1 , 2 , 3 , 4 ]. Ling et al re-sequenced the genome of F. oxysporum f.sp.…”

“…Kurian et al used a specific approach to evaluate the involvement of Ca 2+ signalling machinery components in the regulation of the germ-tube formation, required for initial F. oxysporum colony establishment. These preliminary results may pave the way towards using molecular engineering to control the infection process through signalling pathway component management [ 3 ]. Sophisticated imaging techniques ( egfp- tagged quantitative imaging) coupled with quantitative pathogen detection (qPCR) are often deployed to detect the early stages of infection in plant tissues and track the sequential spread of the pathogen in invaded organs, a strategy employed for F. oxysporum R1 identification in saffron roots and corms [ 4 ].…”