Mutant/mutation
The mutant is a 'Flp/FRT conditional knock-out mutant' of PKAc. The mutant expresses the yeast FlpL recombinase under the control of the trap promoter  and contains a FRTed (part of the) ORF (open reading frame) of the PKAc locus. 

This mutant has been generated by replacement of the endogenous PKAc gene by an PKAc gene with a FRTed ORF in mutant RMgm-4186 that expresses FlpL. This mutant expresses the yeast FlpL recombinase under the control of the promoter of trap and does not contain a selectable marker. The flpl gene is integrated into the silent 230p locus by double cross-over integration.

(Part of)The PKAc ORF is removed from the genome by using the Flp/FRT site-specific recombination (SSR) system (see RMgm-269, RMgm-747). Removal of (part of) the FRTed ORF of PKAc  has been achieved by  transmission of the mutant through mosquitoes, thereby activating expression of the FlpL recombinase in sporozoites that resulted in the excision of the ORF of PKAc which was flanked by FRT sequences.

Protein (function)
cAMP/PKA signaling, known to be a major player in responding to host factors, is stimulated when parasite G-protein-coupled receptors receive extracellular signals and activate adenyl cyclases to produce cAMP. In Plasmodium merozoites, cAMP/PKA signaling plays an essential role in the invasion of erythrocytes by regulating cytosolic Ca++ levels and micronemal protein secretions. Similarly, the PKAc homolog in Toxoplasma gondii (PKAc1) plays a role in invasion via regulation of intracellular calcium. The cAMP-dependent PKA is a key mediator of the signal transduction pathway and plays diverse roles in the cell. The cAMP is generated by adenylyl cyclase, which primarily activates PKA. PKA is known to regulate different processes in eukaryotic cells. In a related apicomplexan parasite T. gondii, PKA has been shown to be involved in tachyzoite to bradyzoite development. PKA phosphorylates apical membrane antigen 1 (AMA1) protein of Plasmodium, and this phosphorylation event is essential for the invasion of new erythrocytes by merozoites. Unsuccesful attempts to disrupt the Plasmodium PKAc gene indicates an essential role in asexual blood stage development/multiplication.

Phenotype
PKAc cKO sporozoites exhibit normal exocytosis and gliding motility and efficiently invade hepatocytes. PKAc cKO parasites develop and egress normally in the liver.
PKAc is essential for hepatic merozoite infectivity. Mice inoculated with different doses of TRAP/FlpL merosomes became positive for blood stage parasites, whereas PKAc cKOmerosomes failed to initiate blood stage infection. Although mice inoculated with high doses of PKAc cKO merosomes became positive, they were carrying intact PKAc locus as revealed by genotyping.
These results demonstrate that PKAc is not important for any stage of preerythrocytic stages, but is essential for erythrocytic stages.

Additional information

Other mutants