Tracking Fungal Growth: Establishment of Arp1 as a Marker for Polarity Establishment and Active Hyphal Growth in Filamentous Ascomycetes.

Anika Groth,Stefanie Pöggeler,Carolin Schunke,Eva Reschka,Daniela Nordzieke

doi:10.3390/jof7070580

Anika Groth, Stefanie Pöggeler + Show 3 more

Open Access

https://doi.org/10.3390/jof7070580

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Abstract

Polar growth is a key characteristic of all filamentous fungi. It allows these eukaryotes to not only effectively explore organic matter but also interact within its own colony, mating partners, and hosts. Therefore, a detailed understanding of the dynamics in polar growth establishment and maintenance is crucial for several fields of fungal research. We developed a new marker protein, the actin-related protein 1 (Arp1) fused to red and green fluorescent proteins, which allows for the tracking of polar axis establishment and active hyphal growth in microscopy approaches. To exclude a probable redundancy with known polarity markers, we compared the localizations of the Spitzenkörper (SPK) and Arp1 using an FM4-64 staining approach. As we show in applications with the coprophilous fungus Sordaria macrospora and the hemibiotrophic plant pathogen Colletotrichum graminicola, the monitoring of Arp1 can be used for detailed studies of hyphal growth dynamics and ascospore germination, the interpretation of chemotropic growth processes, and the tracking of elongating penetration pegs into plant material. Since the Arp1 marker showed the same dynamics in both fungi tested, we believe this marker can be broadly applied in fungal research to study the manifold polar growth processes determining fungal life.

Highlights

Accepted: 18 July 2021Polar tip growth as a form of cell extension is widespread in eukaryotes and can be found in neurons, root hairs, pollen tubes, and at the apex of fungal hyphae [1,2]
As the performed multiple sequence alignment revealed, the actin-related protein 1 (Arp1) protein showed a high amino-acid identify among the clades of Ascomycota, Basidiomycota, and Mucormycota in saprophytic and pathogenic species (Table 2 and Figures S1 and S2)
The ∆Smarp1 strain was arrested in the formation of perithecia and displayed a slow growth velocity even after 10 d of incubation (Figure S4a)

Summary

Introduction

Polar tip growth as a form of cell extension is widespread in eukaryotes and can be found in neurons, root hairs, pollen tubes, and at the apex of fungal hyphae [1,2]. Polar growth allows for radial growth and hyphal network formation by branching followed by the targeted fusion of fungal cells [3,4]. The recruitment of Rho-GTPase Cdc to the new polarity site is crucial for this process [13,15,16,17,18]. As work on Neurospora crassa has shown, a second Rho-GTPase, Rac, is recruited to the polar site and regulates chemotropic growth processes, including germling and hyphal fusion [25].

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