PfACT1 is not required for secretory organelle formation but is crucial for apicoplast segregation. a RAP-treated PfACT1 KO parasites have similar microneme (anti-AMA1), rhoptry (anti-RhopH2) and mitochondria (mito; anti-TOM40) architecture as DMSO controls, as revealed by IFA. b The apicoplast in PfACT1 KO parasites fails to segregate to daughter merozoites and collapses to an amorphous mass close to the food vacuole (white arrow). c IFA of samples drawn at various time points shows that apicoplast reticulation and division increase with nuclear division (DMSO, 20, 40, 44 h). The apicoplast shows close apposition to F-actin staining (zoom, white arrows). Actin staining disappears within 40 h of RAP treatment. The apicoplast does not show reticulation and extensive migration in the absence of PfACT1 (RAP, 40 and 44 h). Scale bar 5 μm. Bottom panel: Super-resolution imaging reveals close apposition of apicoplasts on the actin network. Enlarged inset in ‘merge’ shows apicoplast colocalised to actin filament (white arrows). Colocalisation analysis of apicoplast on actin in the entire image yielded a Manders coefficient of 0.83.Das S, Lemgruber L, Tay CL, Baum J, Meissner M. Multiple essential functions of Plasmodium falciparum actin-1 during malaria blood-stage development. BMC Biol. 2017 Aug 15;15(1):70.