Although apicomplexans lack conventional R-point regulators, presence of the quiescent G1 forms of 43 parasites, including mature T. gondii bradyzoites suggests that a functional RESTRICTION checkpoint 44 exists in apicomplexan parasites. We showed that Cdk-related G1 kinase TgCrk2 forms alternative 45 complexes with atypical cyclins (TgCycP1, TgCycP2 and TgCyc5) in the rapidly dividing developmentally 46 incompetent RH and slower dividing developmentally competent ME49 tachyzoites and bradyzoites. 47 Examination of individual cyclins verified the correlation of cyclin expression with growth dependence and 48 development capacity of type I RH and type II ME49 strains. We demonstrated that rapidly dividing RH 49 tachyzoites are dependent on TgCycP1 and expression of TgCycP1 interferes with bradyzoite 50 differentiation. By using an auxin-induced degradation (AID) model, we established that TgCycP2 51 regulates G1 duration in the developmentally competent ME49 tachyzoites but not in the developmentally 52 incompetent RH tachyzoites. We also tested the functions of TgCycP2 and TgCyc5 in alkaline induced in 53 vitro model and in ex vivo model of spontaneous bradyzoite differentiation (rat embryonic brain cells). 54 Based on functional and global gene expression analyses, we determined that TgCycP2 also regulates 55 bradyzoite replication, while stress- or host-induced TgCyc5 was critical for efficient bradyzoite conversion 56 and tissue cyst maturation.