Regulators of male and female sexual development are critical for the transmission of a malaria parasite.

Malaria transmission to mosquitoes requires a developmental switch in asexually dividing blood-stage parasites to sexual reproduction. In Plasmodium berghei , the transcription factor AP2-G is required and sufficient for this switch, but how a particular sex is determined in a haploid parasite remains unknown. Using a global screen of barcoded mutants, we here identify genes essential for the formation of either male or female sexual forms and validate their importance for transmission. High-resolution single-cell transcriptomics of ten mutant parasites portrays the developmental bifurcation and reveals a regulatory cascade of putative gene functions in the determination and subsequent differentiation of each sex. A male-determining gene with a LOTUS/OST-HTH domain as well as the protein interactors of a female-determining zinc-finger protein indicate that germ-granule-like ribonucleoprotein complexes complement transcriptional processes in the regulation of both male and female development of a malaria parasite. [Display omitted] • A genome-scale screen identifies genes for Plasmodium berghei sexual development • scRNA-seq phenotyping places mutants in the context of a transcriptomic atlas • A LOTUS/OST-HTH domain gene is a conserved factor determining male sex • Protein interactors point to posttranscriptional mechanisms for sex determination Russell et al. systematically reveal early sexual development genes that a malaria parasite requires to infect its mosquito vector. Single-cell phenotyping and protein interactions distinguish between functions in sex determination and development and generate initial insights into mechanisms of how male and female sex are determined in a divergent eukaryote. [ABSTRACT FROM AUTHOR]