Arf6 controls endocytosis and polarity during asexual development of Magnaporthe oryzae

Abstract

Asexual development of phytopathogenic fungi such as Magnaporthe oryzae involves morphological changes that require spatiotemporal regulation of polarized growth. ADP-ribosylation factor 6 (Arf6) is a small GTPase known to regulate membrane trafficking and organization of the actin cytoskeleton at the cell surface, and consequently has an impact on cell morphology and polarity. In this study, we have functionally characterized the Arf6 homolog in M. oryzae, showing that Δarf6 exhibits hyperbranching at hyphal tips and morphologically abnormal conidia as a result of defective polarized growth. Δarf6 hyphae are also defective in endocytosis as evidenced by a significant delay of FM4-64 uptake. Most Δarf6 conidia display reduced conidial length, and have defects in conidial septum formation and nuclear distribution. Furthermore, Δarf6 conidia show a disorganized actin cytoskeleton with random distribution of actin patches at the cell cortex and reduced accumulation of tropomyosin. Arf6-GFP is found to concentrate at the septum area and possibly in endocytic vesicles. Taken together, our data indicate that Arf6 plays an essential role in endocytosis and polarity establishment during asexual development of M. oryzae.