Conjugation-mediated DNA delivery to the filamentous fungus Ustilago maydis

Phytopathogenic fungi are ubiquitous throughout the environment and threaten global food security. This issue is further amplified by the increasing resistance of pathogens to antimicrobials. Current chemical-based antifungals target cells by inhibiting growth or metabolic function, making them ideal for fungal gain of resistance mutations. Biofungicides are a rising class of antifungals that have low potential for negative environmental impact and provide the fungi almost no potential for gaining resistance. Conjugative plasmids which play a role in the natural mechanism of horizontal gene transfer in bacteria, have been repurposed to deliver toxic genetic cargo to recipient cells, showing promise as next-generation antimicrobial agents. In this work, we have demonstrated the first protocol for delivering DNA from Escherichia coli to the filamentous phytopathogen, Ustilago maydis through conjugation. DNA delivery was confirmed using PCR screening of DNA isolated from the re-streaked transconjugants. Although challenges such as reduced conjugation efficiency and extrachromosomal replication persist, this work establishes the first step towards creating a conjugation-based biofungicide.