Mutant/mutation
The mutant lacks expression of PPKL (protein phosphatase containing kelch-like domains).

Protein (function)
PPKL is a distinctive PP1-related enzyme belonging to the PPP family of phosphatases comprising an N-terminal kelch repeat domain and a C-terminal PP1-like phosphatase domain (named PPKL: Protein Phosphatase with Kelch-Like domains). It has been detected in the apicomplexans Cryptosporidium hominis, Toxoplasma gondii and Theileria parva (one gene per genome), as well as in the land plants Arabidopsis thaliana and Oryza sativa (4 and 5 genes respectively). The kelch motif is widespread and involved in many cellular functions, particularly in actin-based cytoskeleton formation and transcriptional regulation. PPKL has only been studied in detail in Arabidopsis thaliana (where it is known as BSU1 or bri1 suppressor1) and along with the kinase BIN2, is involved in brassinosteroid hormone signalling and phosphorylation of the transcription factors BZR1 and BES1

In contrast to the human phosphatome (comprising approximately 156 phosphatases the Plasmodium genome codes for one of the smallest phosphatomes of all the eukaryotic phyla known to date, with 27 putative protein phosphatases falling into four major classes: phosphoprotein phosphatases (PPPs), metallo-dependent protein phosphatases (PPMs), protein tyrosine phosphatases (PTPs) and NLI interacting factor-like phosphatases (NIFs).

Phenotype
Phenotype analyses indicate an essential role of PPKL in maturation of ookinetes.
Deletion of the ppkl gene caused abnormal ookinete development and differentiation, and dissociated apical microtubules from the innermembrane complex, generating an immotile phenotype and failure to invade the mosquito mid-gut epithelium. Evidence is presented for aberrant formation of the apical end and changes in the 'global' protein phosphorylation in the ppkl- mutant ookinetes.

Additional information
PPKL has protein phosphatase enzyme activity, and is highly expressed in female gametocytes and ookinetes. ppkl mRNA is also expressed in asexual blood stages, with the highest expression in schizonts relative to hsp70 and arginyl-tRNA synthetase genes used as controls. Analysis of a mutant expressing GFP-tagged PPKL (RMgm-788) shows that the intensity of PPKL-GFP fluorescence in sexual stages was highest in the nuclear and cytoplasmic compartments of female gametocytes and zygotes, and in the apical cytoplasm of ookinetes. The protein was also detected in oocysts and sporozoites, but was not observed in activated microgametocytes or microgametes

Whether the observed defect was sex-specific was examined by performing genetic crosses between ppkl- parasites and lines deficient in either male (map2-) or female (nek4-) gametes. Cross-fertilization with nek4- parasites did not rescue the phenotype, whereas crossing with map2- gametocytes resulted in 26% of all macrogamete-derived parasites progressing to stage VI, revealing that the requirement for the phosphatase is inherited through the female line.

To assess whether the ablation of oocyst development in ppkl- mutant parasites was also due to a defect in invasion of the midgut epithelium, we bypassed the gut barrier by injecting ppkl- parasites directly into the haemocoel of A. stephensi mosquitoes and analyzed salivary gland invasion 20 days post-injection. Using this method, we found that ppkl- parasites were able to form viable sporozoites, which could migrate to the salivary gland and actively invade.

Other mutants
RMgm-785: An independent mutant lacking expression of PPKL
RMgm-786: A mutant expressing an endogenous GFP-tagged version of PPKL
RMgm-788: An independent expressing an endogenous GFP-tagged version of PPKL