Generating gene silenced mutants in Phytophthora sojae

Phytophthora species are notorious pathogens of plants and cause enormous damage to agriculture. In order to understand Phytophthora pathogenesis, gene silencing and knockout methods are important for the investigation of gene functions. Although CRISPR/Cas9-based gene knockout procedures have been developed in Phytophthora sojae and Phytophthora capsici, it may not always be the best choice especially when knockout mutation leads to lethality. Therefore, gene silencing is a very useful tool for functional analysis of target genes in Phytophthora. This chapter introduces a gene silencing protocol for the soybean pathogen P. sojae. An expression cassette is incorporated into the P. sojae genome through PEG-mediated protoplast transformation, which leads to constitutive production of antisense RNA transcripts. These transcripts are able to target mRNAs through sequence complementarity and effectively reduce the expression of the target genes.