GPS4 IS ALLELIC TO ARL2: IMPLICATIONS FOR GRAVITROPIC SIGNAL TRANSDUCTION
Almost all aspects of plant form and development are impacted by gravity. The most basic of these is gravitropism, a change in the direction of growth in response to a physical reorientation with respect to the gravity vector. However, at 4°C, gravitropic bending is virtually undetectable in wild-type Arabidopsis thaliana (Fukaki et al., 1996), but if plants are returned to vertical at room temperature (RT), transient curvature occurs. This cold effect is known as the Gravity Persistent Signal (GPS) response and is caused by temperature effects on auxin transport (Nadella et al., 2006). To identify genes involved in the signal transduction pathway of gravitropism, a mutant screen was performed to isolate Arabidopsis lines that displayed an aberrant GPS response (referred to here as the GPS treatment) (Wyatt et al., 2002). One of these lines, gravity persistent signal 4 (gps4) showed no response after the GPS treatment (Fig. 3 & Fig. 6). However, room-temperature gravitropism in the inflorescence stem appeared to be unchanged (Fig. 6).