# Homology-mediated transformation of frog-killing fungus Batrachochytrium dendrobatidis illuminates chytrid development and pathogenesis

## TL;DR

Scientists developed a new genetic tool for the frog-killing fungus Bd, enabling targeted gene changes and improving understanding of its pathogenesis.

## Contribution

Established homologous recombination for targeted genetic manipulation in Batrachochytrium dendrobatidis.

## Key findings

- Homologous recombination enables targeted gene deletion and protein tagging in Bd.
- Chitin synthase Myo17D relocates to the plasma membrane during cell wall assembly.
- URA3 gene knockout confirmed via sequencing and drug resistance assays.

## Abstract

The chytrid fungus Batrachochytrium dendrobatidis (Bd) causes chytridiomycosis, a disease driving global amphibian declines. Despite its ecological importance, Bd has been difficult to study at the molecular level due to the lack of genetic tools. Our work establishes homologous recombination as a method to introduce targeted genetic changes in Bd, including the first targeted gene deletion. This system allows us to directly show the function of individual genes in Bd infection. We demonstrate its utility by visualizing Bd infection in live amphibians and confirming the role of chitin synthase in cell wall assembly. This genetic system provides a critical tool for understanding Bd’s biology and pathogenesis, enabling future studies that could inform conservation efforts.

The chytrid fungus Batrachochytrium dendrobatidis (Bd) infects amphibians and causes chytridiomycosis, a disease linked to global amphibian decline. Despite its ecological importance, Bd has lacked robust tools for genetic manipulation, limiting molecular insights into its development and pathogenicity. Here, we establish homologous recombination as a system for stable transformation of Bd, enabling targeted chromosomal integration of exogenous DNA, endogenous protein tagging, and targeted gene deletion. We use this system to visualize Bd infection in live amphibians to enhance understanding of host invasion and pathogenesis. We also use this system to test a previous hypothesis regarding the role of chitin synthases in Bd development by tagging the endogenous chitin synthase Myo17D and observing its rapid relocalization to the plasma membrane during de novo cell wall assembly. Finally, we use our homologous recombination approach for targeted gene deletion by knocking out the URA3 locus, and confirm the resulting genotype and phenotype via sequencing and drug resistance assays. This genetic transformation system offers a foundational tool for molecular studies of Bd, advancing our capacity to dissect molecular mechanisms of chytrid pathogenesis.