Mutant/mutation
The mutant expresses a C-terminal 3xHA-tagged version of SOC1 and expresses RFP and GFP in female and male gametocytes, respectively.

Protein (function)
The protein is identified in a screen for proteins that are phosphorylated by CDPK4.CDPK4 has an essential role in male (micro)gamete formation (exflagellation).
Among these proteins, it was decided to name those without predicted function SOC, for substrate of CDPK4. Ten proteins were indeed conserved Plasmodium proteins of unknown function and one  protein, SOC2, was annotated as cyclin-related protein 2 but it was suggested be unrelated to cyclins. Also GAP40 was identified.
To investigate the roles of SOC1 to 4 and GAP40 during gametogenesis, it was attempted to individually  knock-out their encoding proteins. As controls, soc5 and soc6 were included that were not differentially phosphorylated in a CDPK4-KO mutant. For gap40 no transgenic parasites could be obtained. Viable KO parasites could be detected in mixed asexual stages for six genes and non-clonal populations were first assessed for microgametocyte DNA replication and exflagellation. No defects were observed in the SOC4-KO line as well as in the SOC5-KO and SOC6-KO control lines suggesting that these proteins do not represent crucial CDPK4 effectors in the regulation of male gametogenesis. Defects in DNA replication or exflagellation were observed for SOC1-KO, SOC2-KO, and SOC3-KO lines that were cloned for in depth characterisation. 

Although no domain could be identified in SOC1, this protein was found to be conserved in eukaryotes. Eukaryotic homologues contained SAPS domains that have been found to be involved in G1 to S-phase transitions by associating to SIT4 phosphatase

Phenotype
Analysis of localisation of SOC1 tagged with HA (SOC1-3xHA) did not show a significant enrichment in the nucleus but rather showed a diffuse cytoplasmic localisation in male gametocytes.

Phenotype analyses of a mutant lacking expression of SOC1 (RMgm-4143) showed the following: Slightly reduced growth/multiplication of asexual blood stages.
Strongly reduced exflagellation (male gamete formation). Reduced DNA replication during male gamete formation (partially blocked at 1N; 50% of microgametocytes remained haploid; 40% of SOC1-KO microgametocytes reached the octoploid state).

Additional information

Other mutants