Mutant/mutation
The mutant lacks expression of the rhomboid protease ROM1.

Protein (function)
Rhomboid proteins are intra-membrane proteases that play a role in multiple processes. They belong to a family of serine proteases that cleave cell-surface proteins within their transmembrane domains. The Plasmodium  genome encodes a total of 8 rhomboid proteases (ROM1, 3, 4, 6, 7, 8, 9 and 10).  ROM1 is expressed in both the blood stages and mosquito stages (sporozoites). ROM1 was localized to organelles of the apical complex of merozoites. In vitro  substrates of  P. falciparum ROM1 include the merozoite-specific proteins AMA1 (apical membrane antigen 1) and proteins of the EBL (erythrocyte binding ligands) and RBL (reticulocyte binding ligands) families as well as several proteins of the invasive ookinete- and sporozoite-stages, such as TRAP (thrombospondin-related anonymous protein), CTRP (circumsporozoite- and TRAP-related protein) and MAEBL (merozoite adhesive erythrocytic binding protein). 
In P. falciparum  only a small fraction of AMA1 is shed by ROM1 and the intramembrane cleavage can be reduced to undetectable levels by mutagenesis without discernible phenotypic consequences. The successful generation of P. berghei and P. yoelii  mutants that lack expression of ROM1 (see below) also demonstrates that ROM1 is not essential for blood stage multiplication

Phenotype
The phenotype analyses indicate that ROM1 is not essential throughout the complete life cycle in P. berghei.
Liver-stage development was reduced as shown by a 1-day extension of the prepatent period in mice following the inoculation with 10(4) purified sporozoites.
While gliding motility and the rate of cell traversal of sporozoites were similar to wild type parasites,  in two out of three experiments a reduction in sporozoite in vitro invasion rates was observed that could explain (in part) the delay in the prepatent period. Immunofluorescence analyses of liver stage parasites stained with antibodies against markers for parasite development (HSP70), PVM (UIS4 and EXP1) and merozoite formation (MSP1), revealed no distinct differences in morphology and size between ∆rom1 and wild type liver stages at 24h or 48h after sporozoite invasion.

Additional information
It has been reported that P. berghei  and P. yoelii mutants lacking ROM1 (see mutants RMgm-176, RMgm-659) exhibit a slight growth delay and appear less virulent in mice than wild type parasites. In contrast, the ∆rom1 mutant described here and in RMgm-761 neither a growth nor a virulence-attenuation phenotype have been detected. Mice infected with ∆rom1 parasites showed a normal course of infection and all C57BL/6 mice developed clear signs of experimental cerebral malaria (ECM). The cause for these discrepancies in blood stage phenotypes between the ∆rom1 P. berghei  mutants described here and in RMgm-761 and the mutant RMgm-176 is unknown. In RMgm-176 the mutant clone examined was derived from a single transfection experiment.
Although a significant reduction in expression of UIS4 has been reported for liver stages of P. yoelii  mutants lacking expression of ROM1 (RMgm-659), the ∆rom1 parasites showed only a slight, but not significant, reduction in liver-stages as determined by UIS4 staining and the liver stages of the ∆rom1 mutant had no unusual parasitophorous vacuole membrane as reported for the P. yoelii  mutants. Liver stages of ∆rom1 and wild-type parasites were also comparable in size at 48 hrs post infection.

Other mutants
RMgm-176: A P. berghei mutant lacking expression of rhomboid protease ROM1 (partial disruption)
RMgm-761: A P. berghei mutant lacking expression of rhomboid protease ROM1 (complete disruption)
RMgm-178: A P. berghei mutant lacking expression of rhomboid protease ROM3
RMgm-762: A P. berghei mutant lacking expression of rhomboid protease ROM9
RMgm-179: A P. berghei mutant lacking expression of rhomboid protease ROM10


RMgm-187: Unsuccessful attempts to disrupt P. berghei rhomboid protease rom4
RMgm-758: Unsuccessful attempts to disrupt P. berghei rhomboid protease rom6
RMgm-759: Unsuccessful attempts to disrupt P. berghei rhomboid protease rom7
RMgm-760: Unsuccessful attempts to disrupt P. berghei rhomboid protease rom8

RMgm-763: A P. berghei mutant expressing  a (C-terminal) GFP-tagged version of rhomboid protease ROM3
RMgm-764: A P. berghei mutant expressing  a (C-terminal) mCherry-tagged version of rhomboid protease ROM4

RMgm-659: A P. y. yoelii 17XNL mutant lacking expression of rhomboid protease ROM1
RMgm-660: A P. y. yoelii 17XNL mutant expressing  a (N-terminal) HA-tagged version of rhomboid protease ROM1