Mutant/mutation
The mutant expresses azamiGFP (AGFP) under control of the 5'- and 3'-UTR region of sdha (flavoprotein subunit of succinate dehydrogenase) and fused the first 60 amino acids of sdha. It is reported that the first 60 amino acids of P. falciparum flavoprotein contains a functional mitochondrial targeting signal The fusion transgene of AGFP and sdha is integrated by single cross-over recombination into the sdha locus resulting in the presence of the transgene and a normal copy of sdha.

Protein (function)
In other eukaryotes, pyruvate dehydrogenase is localized in mitochondria where it links the glycolysis metabolic pathway to TCA cycle, while it is localized in the apicoplast in P. falciparum. Blood-stage P. falciparum have only a single mitochondrion without crista. Such morphologically immature mitochondrion suggests that, unlike other eukaryotes, the blood-stage P. falciparum relies mainly on cytoplasmic glycolysis for their energy metabolism but not on mitochondrial oxidative phosphorylation. P. falciparum express all TCA cycle enzyme genes and most ones for the electron transport chain (ETC). The genes for TCA cycle are up-regulated at mosquito stages. The gametocytes, precursor cells of gametes possess mitochondria with cristae. These data suggest that mitochondrial energy metabolism may have more crucial roles in insect stages than blood stages. The mitochondrial complex II (succinate-ubiquinone reductase: SQR) oxidizes succinate to produce fumarate as a TCA cycle member enzyme. In the anaerobic electron transfer system, complex II carries out fumarate reduction using quinol as an electron donor (quinol-fumarate reductase; QFR), which is the reverse reaction of SQR. Complex II consists of four subunits, flavoprotein (Fp), iron-sulfur cluster protein (Ip) and two small membrane anchor subunits, cytochrome b large (CybL) and small (CybS) subunits. The Fp with molecular mass of 70 kDa has a flavin adenine dinucleotide (FAD) covalently bound to a highly conserved histidine (His) residue. Fp and Ip form catalytic portion of the complex and this portion act as a succinate dehydrogenase (SDH), catalyzing the oxidation of succinate by water-soluble electron acceptors such as phenazine methosulfate (PMS) in SQR, while it acts as a fumarate reductase (FRD), catalyzing electron transfer from water-soluble electron donors such as reduced methylviologen (MV) to fumarate in QFR. FAD in the Fp receives the reducing equivalents from succinate and then transfers it to quinone by SQR activity where the two small membrane anchor subunits are indispensable (10). Thus, complex II functions as a link between the TCA cycle and the ETC, directly. While complex II has such critical roles in energy metabolisms and Fp and Ip subunits genes are substantially conserved in various organisms, two small membrane anchor subunit genes are diverse. However, evidence for the presence of genes in the Plasmodium genome encoding mitochondrial Complex II subunits SDH3 and SDH4 and ATP synthase subunits a and b.

Phenotype
Phenotype analyses of mutants lacking expression of SDHA (RMgm-753) indicate a non-essential function of SDHA for asexual blood stages. Phenotype analyses of these mutants indicate an essential function of SDHA for ookinete and/or oocyst formation. Normal numbers of gametocytes are produced and male gamete formation (exflagellation) is normal. The conversion rate of female gametes to ookinetes in vitro of Pbsdha(-) is significantly reduced to 17% of wild type parasites. No oocysts are formed.
Phenotype analyses of the mutant Pbsdha::AGFP expressing the fusion of AGFP and SDHA indicate expression in blood stage trophozoites and schizonts and in ookinetes, oocysts and sporozoites. GFP signals co-localized with MitoTracker Orange signals

Additional information

Other mutants
RMgm-753: A mutant lacking expression of SDHA