A Novel Spo11 Homologue Functions as a Positive Regulator in Cyst Differentiation in .

persists in a dormant state with a protective cyst wall for transmission. It is incompletely known how three cyst wall proteins (CWPs) are coordinately synthesized during encystation. Meiotic recombination is required for sexual reproduction in animals, fungi, and plants. It is initiated by formation of double-stranded breaks by a topoisomerase-like Spo11. It has been shown that exchange of genetic material in the fused nuclei occurs during encystation, suggesting parasexual recombination processes of this protozoan. possesses an evolutionarily conserved Spo11 with typical domains for cleavage reaction and an upregulated expression pattern during encystation. In this study, we asked whether Spo11 can activate encystation process, like other topoisomerases we previously characterized. We found that Spo11 was capable of binding to both single-stranded and double-stranded DNA in vitro and that it could also bind to the promoters in vivo as accessed in chromatin immunoprecipitation assays. Spo11 interacted with WRKY and MYB2 (named from myeloblastosis), transcription factors that can activate gene expression during encystation. Interestingly, overexpression of Spo11 resulted in increased expression of - and genes and cyst formation. Mutation of the Tyr residue for the active site or two conserved residues corresponding to key DNA-binding residues for Spo11 reduced the levels of and gene expression and cyst formation. Targeted disruption of gene with CRISPR/Cas9 system led to a significant decrease in and gene expression and cyst number. Our results suggest that Spo11 acts as a positive regulator for differentiation into cyst.