Spatiotemporal regulation of Rho 1 and Cdc 42 activity during C andida albicans filamentous growth

Summary Rho G ‐proteins are critical for polarized growth, yet little is known about the dynamics of their activation during fungal filamentous growth. We first investigated the roles of Rho 1 and Rho 2 during C andida albicans filamentous growth. Our results show that Rho 1 is required for invasive filamentous growth and that Rho 2 is not functionally redundant with Rho 1. Using fluorescent reporters, we examined the dynamics of the active form of Rho 1 and Cdc 42 during initiation and maintenance of hyphal growth. Quantitative analyses indicated that the distribution, but not the level, of these active G ‐proteins is altered during initial polarization upon germ tube emergence. A comparison of the dynamics of these active G ‐proteins during budding and hyphal growth indicates that a higher concentration of active Cdc 42 was recruited to the germ tube tip than to the bud tip. During hyphal elongation, active Cdc 42 remained tightly restricted to the hyphal tip, whereas active Rho 1 was broadly associated with the apex and subsequently recruited to the cell division site. Furthermore, our data suggest that phosphoinositide‐bis‐phosphates are critical to stabilize active Rho 1 at the growth site. Together, our results point towards different regulation of Cdc 42 and Rho 1 activity during initiation and maintenance of filamentous growth.