Abscisic acid controls calcium-dependent egress and development in Toxoplasma gondii

Calcium signalling plays an important role in determining the virulence of the human pathogen Toxoplasma gondii, an apicomplexan protozoon. A study of the mechanisms involved has uncovered a surprising agent for this signalling: the plant hormone abscisic acid. Comparative genomics reveals that the pathway for synthesis of the plant hormone was acquired by endosymbiosis. This pathway controls a crucial developmental switch between lytic growth and dormancy, which is a key component of pathogenesis. The plant-like nature of this pathway may be exploited to develop new therapeutics as shown by the ability of a specific inhibitor of abscisic acid biosynthesis to protect mice from lethal infection.