Mutant/mutation
The mutant lacks expression of ALAS and expresses GFP under control of the strong hsp70 promoter

Protein (function)
The malaria parasite is capable of de novo heme biosynthesis despite its ability to acquire heme from red blood cell (RBC) hemoglobin. The first enzyme of the de novo heme-biosynthetic pathway, δ-aminolevulinate synthase (ALAS) and the last two enzymes, Protoporphyrinogen IX oxidase (PPO) and Ferrochelatase (FC) localize to the mitochondrion. The enzymes that catalyze the intermediate steps: ALA dehydratase (ALAD), Porphobilinogen deaminase (PBGD) and Uroporphyrinogen III decarboxylase (UROD) localize to the apicoplast.

Phenotype
Mutant parasites showed normal blood stage development, indicating a non-essential role of ALAS during blood stage development. Normal numbers of oocysts are formed. However, day 10 and 14 oocysts had a reduced size (`60%) compared to wild type oocysts. A large (~10-20-fold) reduction in the numbers of midgut-associated sporozoites was observed. No hemocoel or salivary gland sporozoites were detected.
However, when mosquitoes were fed with ALA-supplement (in the drinking water), sporozoite production was restored and mutant sporozoites were able to infect hepatocytes like wild type sporozoites. Liver stages could mature and produce infectious merozoites, although at a reduced rate.

Additional information
In this study, the essentiality of heme biosynthesis was systematically profiled by targeted gene deletion of enzymes in early steps of this pathway. It was shown that disruption of endogenous heme biosynthesis leads to a first detectable defect in oocyst maturation and sporogony in the Anopheles vector, whereas blood stage propagation, colonization of mosquito midguts or initiation of oocyst development occurs indistinguishable from wild-type parasites. Although sporozoites are produced by parasites lacking an intact pathway for heme biosynthesis, they are absent from mosquito salivary glands, indicative of a vital role for heme biosynthesis only in sporozoite maturation. Rescue of the first defect in sporogony permitted analysis of potential roles in liver stages. It was shown that liver stage parasites benefit from, but do not strictly depend upon their own aminolevulinic acid synthase and that they can scavenge aminolevulinic acid from the host environment.

Some results in this paper are different from other analyses of mutants lacking expression of ALAS. See mutant RMgm-924 that showed strongly reduced oocyst production and absence of liver stage development.

Other mutants