Phytohormones regulate asexual Toxoplasma gondii replication

The protozoan Toxoplasma gondii (T. gondii) is a zoonotic disease agent causing systemic infection in warm-blooded intermediate hosts including humans. During the acute infection, the parasite infects host cells and multiplies intracellularly in the asexual tachyzoite stage. In this stage of the life cycle, invasion, multiplication, and egress are the most critical events in parasite replication. T. gondii features diverse cell organelles to support these processes, including the apicoplast, an endosymbiont-derived vestigial plastid originating from an alga ancestor. Previous studies have highlighted that phytohormones can modify the calcium-mediated secretion, e.g., of adhesins involved in parasite movement and cell invasion processes. The present study aimed to elucidate the influence of different plant hormones on the replication of asexual tachyzoites in a human foreskin fibroblast (HFF) host cell culture. T. gondii replication was measured by the determination of T. gondii DNA copies via qPCR. Three selected phytohormones, namely abscisic acid (ABA), gibberellic acid (GIBB), and kinetin (KIN) as representatives of different plant hormone groups were tested. Moreover, the influence of typical cell culture media components on the phytohormone effects was assessed. Our results indicate that ABA is able to induce a significant increase of T. gondii DNA copies in a typical supplemented cell culture medium when applied in concentrations of 20 ng/μl or 2 ng/μl, respectively. In contrast, depending on the culture medium composition, GIBB may potentially serve as T. gondii growth inhibitor and may be further investigated as a potential treatment for toxoplasmosis.