Formin-2 drives polymerisation of actin filaments enabling segregation of apicoplasts and cytokinesis in Plasmodium falciparum

Abstract

In addition to its role in erythrocyte invasion, <i>Plasmodium falciparum</i> actin is implicated in endocytosis, cytokinesis and inheritance of the chloroplast-like organelle called the apicoplast. Previously, the inability to visualise filamentous actin (F-actin) dynamics had restricted the characterisation of both F-actin and actin regulatory proteins, a limitation we recently overcame for <i>Toxoplasma</i> (Periz et al, 2017). Here, we have expressed and validated actin-binding chromobodies as F-actin-sensors in <i>Plasmodium falciparum</i> and characterised <i>in-vivo</i> actin dynamics. F-actin could be chemically modulated, and genetically disrupted upon conditionally deleting <i>actin-1</i>. In a comparative approach, we demonstrate that Formin-2, a predicted nucleator of F-actin, is responsible for apicoplast inheritance in both <i>Plasmodium</i> and <i>Toxoplasma</i>, and additionally mediates efficient cytokinesis in <i>Plasmodium</i>. Finally, time-averaged local intensity measurements of F-actin in <i>Toxoplasma</i> conditional mutants revealed molecular determinants of spatiotemporally regulated F-actin flow. Together, our data indicate that Formin-2 is the primary F-actin nucleator during apicomplexan intracellular growth, mediating multiple essential functions.