CRISPR-Mediated Editing of Rice False Smut Fungus

The fungus Ustilaginoidea virens causes rice false smut, a major disease of rice (Oryza sativa). However, there are only limited molecular studies on this pathogen due to the lack of techniques for studying targeted gene disruption mutants. The research team of Yafeng Liang from the Northwest A&F University in China used the CRISPR-Cas9 system to generate mutants with deleted USTA ustiloxin and UvSLT2 MAP kinase genes.

Three gRNAs targeting USTA, namely UA01, UA13, and UA21, were transformed into U. virens. For all three, the gene replacement frequency was higher when the Cas9 and gRNA constructs were transformed on the same vector. UA01 had the highest knockout frequency of 90% for generating ustA mutants. No off-target mutations were detected in the ustA mutants generated via any of the three gRNAs.

For UvSLT2, the gene replacement frequency was 50% with CRISPR-Cas9. While ustA mutants had no detectable phenotypes, Uvslt2 mutants had slightly reduced growth rate and had over 70% reduction in conidiation. Deletion of UvSLT2 also increased sensitivity to cell wall stresses but tolerance to hyperosmotic or oxidative stresses.

These results showed that the CRISPR-Cas9 system can be used as an efficient gene editing approach in U. virens and could be used to develop varieties resistant to false smut.

For more information, read the article in Frontiers in Plant Science.