Genetic transformation of Spizellomyces punctatus, a resource for studying chytrid biology and evolutionary cell biology.

Edgar M Medina,Giuseppe Ianiri,Caroline Laplante,Nicolas E Buchler,Kimberly Bellingham-Johnstun,Kristyn A Robinson,Lillian K Fritz-Laylin

doi:10.7554/elife.52741

Edgar M Medina, Giuseppe Ianiri + Show 5 more

Open Access

https://doi.org/10.7554/elife.52741

Copy DOI

Abstract

Chytrids are early-diverging fungi that share features with animals that have been lost in most other fungi. They hold promise as a system to study fungal and animal evolution, but we lack genetic tools for hypothesis testing. Here, we generated transgenic lines of the chytrid Spizellomyces punctatus, and used fluorescence microscopy to explore chytrid cell biology and development during its life cycle. We show that the chytrid undergoes multiple rounds of synchronous nuclear division, followed by cellularization, to create and release many daughter 'zoospores'. The zoospores, akin to animal cells, crawl using actin-mediated cell migration. After forming a cell wall, polymerized actin reorganizes into fungal-like cortical patches and cables that extend into hyphal-like structures. Actin perinuclear shells form each cell cycle and polygonal territories emerge during cellularization. This work makes Spizellomyces a genetically tractable model for comparative cell biology and understanding the evolution of fungi and early eukaryotes.

Highlights

Zoosporic fungi, commonly referred to as ‘chytrids’, span some of the deepest fungal Phyla and comprise much of the undescribed environmental fungal DNA diversity in aquatic ecosystems (James et al, 2006; Richards et al, 2012; Powell and Letcher, 2014; Grossart et al, 2016)
Because Agrobacterium-mediated transformation has been adapted for transformation of diverse animals and fungi (Bundock et al, 1995; Kunik et al, 2001; Covert et al, 2001; Ianiri et al, 2017; Vieira and Camilo, 2011), we chose to use this system in Spizellomyces punctatus
We identified and tested native Spizellomyces promoters, including a divergent H2A/H2B promoter that can simultaneously express Hygromycin resistance and a gene of interest throughout the chytrid life cycle

Summary

Introduction

Commonly referred to as ‘chytrids’, span some of the deepest fungal Phyla and comprise much of the undescribed environmental fungal DNA diversity in aquatic ecosystems (James et al, 2006; Richards et al, 2012; Powell and Letcher, 2014; Grossart et al, 2016). Chytrids are unique in that they have retained ancestral cellular features, shared by animal cells and amoebae, while having fungal features. Chytrids begin their life as motile zoospores that lack a cell wall, swim with a single posterior cilium nucleated from a centriole, and crawl across surfaces (Fuller, 1976; Sparrow, 1960; Deacon and Saxena, 1997; Held, 1975; FritzLaylin et al, 2017b). Later life cycle stages exhibit fungal characteristics including the formation of chitinous cell walls, the growth of hyphal-like structures, and the development of a sporangium (sporangiogenesis); see Figure 1. The formation of a multinuclear compartment followed by cellularization is reminiscent of development in flies (e.g. Drosophila), amoeba (e.g. Physarum), and protozoa (e.g. Plasmodium).

Methods

Results

Conclusion