Plasmodium falciparum gametogenesis essential protein 1 (GEP1) is a transmission-blocking target.

Transmission of Plasmodium parasites to Anopheles mosquitoes relies on rapid activation of mature gametocytes in the midgut, triggered by a temperature drop and xanthurenic acid. In Plasmodium yoelii, the gametogenesis essential protein 1 (GEP1) was linked to xanthurenic acid (XA)-dependent gamete activation. We characterized GEP1 in Plasmodium falciparum using CRISPR-Cas9 to create PfGEP1 loss-of-function lines. These lines failed to undergo male or female gametogenesis, even when stimulated by XA or a temperature drop. The defect persisted despite treatment with the phosphodiesterase inhibitor Zaprinast. Analysis of field samples revealed two GEP1 single-nucleotide polymorphisms (V241L and S263P) in 12% and 20% of 49 cases. Our findings confirm GEP1's essential role in gamete activation, highlight an XA-independent function, and support its potential as a transmission-blocking target. Impact statement For sustainable malaria control, transmission-blocking drug targets are urgently needed. Work in murine models showed that GEP1 is a candidate. We show complete block of life cycle progression of the human malarial parasite Plasmodium falciparum when GEP1 is deleted, warranting targeted drug development to achieve gamete-free mosquito blood meals.