Abstract
Luciferase reporter system was used for the measurement of AUX/IAA19 expression in Arabidopsis. Application of 100 nM NAA induced a transient increase of the luciferase signal in both wt and the dominant mutant, msg2-1. The basal expression level and maximum auxin response were low in msg2-1, which was consistent with previous report (Tatematsu et al., 2004). The supposed accumulation of msg2-1 protein with a long half-life may attribute to the defects. Kinetic analysis suggested that the inhibitory effect of msg2-1 protein was only observed 1 h after NAA application. This may explain why msg2-1 showed wild-type response in root gravitropism. In fact, when we applied longer presentation time of gravi-stimulation for root tips, msg2-1 roots showed a reduced gravitropism, ie, plagiotropism. These observations suggest that a combination of multiple AUX/IAAs with different half-life may determine gravity setpoint angle (GSA) of root and may be one of the critical factors to exert a plagiotropism in the root system.
