AP2X-1 is a negative regulator of Toxoplasma gondii sexual commitment
Toxoplasma gondii is a ubiquitous protozoan with a complex life cycle involving transitions between different hosts and developmental stages, each adapted to a unique niche within its host. However, the regulatory mechanisms controlling these life cycle transitions remain poorly understood. In this study, we characterized the AP2 factor AP2X-1, which is expressed during the tachyzoite and bradyzoite stages, but not in the mature merozoite stage. Knockout of ap2X-1 significantly impaired tachyzoite invasion and replication, while increasing the frequency of bradyzoite differentiation. As a component of the HDAC3/MORC complex, knockout of ap2X-1 led to the upregulation of bradyzoite and sexual stage-specific genes. Single-cell sequencing revealed that ap2X-1 knockout strains behaved as a mixed population of tachyzoites, bradyzoites, merozoites, and sporozoites. CUT&Tag analysis revealed substantial overlap between AP2X-1 and HDAC3/MORC complex binding at the promoters of bradyzoite and sexual stage-specific genes. Additionally, ATAC-seq analysis demonstrated that AP2X-1 modulates chromatin compaction and accessibility, suggesting that AP2X-1 recruits the HDAC3/MORC complex to repress bradyzoite differentiation and sexual commitment. The loss of ap2X-1 resulted in significant attenuation of T. gondii virulence and reduced the formation of brain cysts in vivo. These findings identify AP2X-1 as a critical negative regulator of T. gondii sexual development. Overall design: We report genome-wide AP2X-1 profiles in Toxoplasma gondii using CUT&TAG We report  chromatin compaction and accessibility of AP2X-1 in Toxoplasma gondii using ATAC-Seq.