Global transcriptional repression: An initial and essential step for Plasmodium sexual development

Significance In malaria parasites, gametocytogenesis is a process whereby gametocytes, the precursors of gametes, are generated from asexual blood-stage parasites. In this study, we report that the plasmodium transcriptional repressor AP2-G2 plays an essential role in this process. We found that AP2-G2 represses the genes that are required for the proliferation of the asexual stage and, thereby, supports the conversion from the asexual blood stage to the nonreplicative sexual stage. Similarly, during the initial phase of germ-line formation in metazoan animals (including insects), a master transcriptional repressor specifies primordial germ cells among embryonic cells. Thus, our findings suggest that the basic molecular mechanisms that are required to establish the germ line have been conserved in eukaryotes, despite their evolutionary divergence. Gametocytes are nonreplicative sexual forms that mediate malaria transmission to a mosquito vector. They are generated from asexual blood-stage parasites that proliferate in the circulation. However, little is known about how this transition is genetically regulated. Here, we report that an Apetala2 (AP2) family transcription factor, AP2-G2, regulates this transition as a transcriptional repressor. Disruption of AP2-G2 in the rodent malaria parasite Plasmodium berghei did not prevent commitment to the sexual stage but did halt development before the appearance of sex-specific morphologies. ChIP-seq analysis revealed that AP2-G2 targeted ∼1,500 genes and recognized a five-base motif in their promoters. Most of these target genes are required for asexual proliferation of the parasites in the blood, suggesting that AP2-G2 blocks the program that precedes asexual replication to promote conversion to the sexual stage. Microarray analysis showed that the identified targets constituted ∼70% of the up-regulated genes in AP2-G2–depleted parasites, suggesting that AP2-G2 actually functions as a repressor in gametocytes. A promoter assay using a centromere plasmid demonstrated that the binding motif functions as a cis-acting negative regulatory element. These results suggest that global transcriptional repression, which occurs during the initial phase of gametocytogenesis, is an essential step in Plasmodium sexual development.