Initial fungal effector production is mediated by early endosome motility

Fungal plant pathogenicity is facilitated by effector proteins that are specifically expressed during infection and are responsible for suppressing plant defense mechanisms. Recent studies have elucidated the detailed molecular mechanisms of effector action throughout fungal infection. However, little is known about the trafficking and secretion of effectors in fungal hyphae during the initial stage of infection. Using state-of-the-art microscopy we have demonstrated that early endosome (EE) motility is required for effector production during fungal infection. Moreover, the MAPK Crk1 has been shown to travel on EEs and to function as a negative regulator of effector expression, suggesting that motile EEs are involved in signal transduction. Here I further discuss possible mechanisms whereby EE motility regulates effector expression in the initial stages of infection.