Lateral root meristem establishment by LRIS in Arabidopsis
Previous transcript profiling of the Arabidopsis LRIS only occurred after 2 and 6 hours of NAA treatment (Himanen et al., 2004, Vanneste et al., 2005, De Smet et al., 2008). Here, we extended the time-course of the Arabidopsis LRIS to capture the expression during primordium formation. Therefore, we first characterized lateral root primordium development in the Arabidopsis LRIS, and performed staging in different regions of the root. We observed a slight loss of the synchronization in higher parts of the root. Nevertheless at 1 to 2 mm distance from the root tip, different stages of primordia were highly synchronously induced, and stage I, II and III primordia could be observed at 12, 18 and 24 hours after NAA treatment, respectively.  We therefore sampled the 1 to 2 mm region from the root tip at 0, 12, 18 and 24 hours in the Arabidopsis LRIS, to sample stage I, II and III primordia, respectively.