A Call for a Better Understanding of Aquatic Chytrid Biology

Abstract

The phylum Chytridiomycota (the “chytrids”) is an early-diverging, mostly unicellular, lineage of fungi that consists of significant aquatic saprotrophs, parasites, and pathogens, and is of evolutionary interest because its members retain biological traits considered ancestral in the fungal kingdom. While the existence of aquatic chytrids has long been known, their fundamental biology has received relatively little attention. We are beginning to establish a detailed understanding of aquatic chytrid diversity and insights into their ecological functions and prominence. However, the underpinning biology governing their aquatic ecological activities and associated core processes remain largely understudied and therefore unresolved. Many biological questions are outstanding for aquatic chytrids. What are the mechanisms that control their development and life cycle? Which core processes underpin their aquatic influence? What can their biology tell us about the evolution of fungi and the wider eukaryotic tree of life? We propose that the field of aquatic chytrid ecology could be further advanced through the improved understanding of chytrid biology, including the development of model aquatic chytrids and targeted studies using culture-independent approaches.

A cellular and molecular atlas reveals the basis of chytrid development

“…The apophysis is ubiquitous across the Chytridiomycota (James et al, 2006), but the function of the structure is poorly understood (Laundon and Cunliffe, 2021). Here we show that the apophysis exhibits high endomembrane density and active intracellular trafficking between the feeding rhizoids and cell body (Fig.…”

“…The cell plan of the immature thallus can be divided into three parts (Fig. 1B): the cell body which is ultimately destined for reproduction (zoosporogenesis), the rhizoid for attachment and feeding, and (in some chytrid species) a bulbous swelling between the cell body and rhizoid termed the 'apophysis', the function of which is currently poorly understood (Laundon and Cunliffe, 2021). The final life stage is the reproductive 'mature zoosporangium', which appears once the immature thallus has reached maximum cell size and the cell body cytoplasm is cleaved into the next generation of zoospores (Fig.…”

“…R. globosum JEL800 exhibits an archetypal chytrid cell plan (Fig. 1B) and rapid life cycle, making it a useful model system to interrogate cellular development (Laundon et al, 2020;Laundon and Cunliffe, 2021).…”

A cellular and molecular atlas reveals the basis of chytrid development

“…This makes chytrids powerful models to explore the origin and evolution of innovations in fungal cell biology and the wider eukaryotic tree of life. To help fully appreciate chytrids in terms of their ecological and evolutionary contexts, it is necessary to resolve their core cell biology ( Laundon and Cunliffe, 2021 ).…”

“… ( A ) Chytrids (phylum Chytridiomycota) are a major fungal lineage, many members of which exhibit cellular characteristics retained from the last common ancestor of branching (rhizoidal and hyphal) fungi (star). Simplified phylogenetic tree from Laundon and Cunliffe, 2021 ; Tedersoo et al, 2018 . ( B ) Rhizoclosmatium globosum exhibits an archetypal chytrid life cycle and cell plan delineated here into four discrete major stages.…”