Research focus

​Plant roots serve a multitude of functions. They anchor and supply plants with water and nutrients, and exchange various growth substances with the shoots. Over the last ten years, Arabidopsis thaliana has been proven to be an efficient model plant for studying root development. Besides the various advantages this plant offers in genetic and molecular studies, the Arabidopsis root boasts quite predictable ontogeny, very simple anatomy and a high level of transparency, making it extremely suitable for morphogenetic and cell-biology studies. Understanding how root systems develop is crucial for maximizing crop production in a world in which the population is increasing and the amount of arable land is decreasing. Lateral root formation or root branching is one of the major regulators of root-system architecture. During root branching, developmental and environmental controls of cell-cycle regulation are crucial. Mitotic activity must be renewed in differentiated pericycle cells that have left the cell cycle. In Arabidopsis, the lateral roots are initiated by local activation of the pericycle cells at the xylem poles (Casimiro et al., 2003). Unique cell-cycle control, dissimilar from that in other pericycle cells, was shown to take place in the xylem pericycle (Beeckman et al., 2001). Good knowledge of this tissue-specific cell-cycle regulation is therefore needed for better understanding of lateral root initiation.
  
To efficiently study the molecular and cytological events during the early stages of pericycle activation, a lateral root-inducible system was developed. Successive treatments with an auxin transport inhibitor and exogenous auxin were used to prevent the first formative divisions and to activate the whole pericycle, respectively. In this system, cell-cycle progression during the early course of lateral root induction was monitored using histochemical and molecular techniques. The results demonstrated that the CDK inhibitory proteins (KRPs) play a previously unknown role in specifically preventing lateral root initiation at the G1-tot-S transition (Himanen et al., 2002). To date, the signaling cascade towards the specification of the lateral root founder cells and the asymmetric divisions is not elucidated, and represents the major theme of our current research. Three independent but complementary transcript profiling studies have been performed using the lateral root inducible system (Himanen et al., 2004, Vanneste et al., 2005; De Smet et al., in prep.). Based on the global changes in the transcriptome during the initial phase of lateral root induction, functional analyses of potential key-regulators for root branching are currently being analyzed.