Abstract
In most dicot plants, lateral root (LR) formation, which is important for the construction of root system, is initiated from asymmetric cell divisions (ACDs) of the xylem pole pericycle cells of the parent roots such as the primary root and the existing lateral roots. In Arabidopsis, two Auxin Response Factors, ARF7 and ARF19, positively regulate LR formation through activation of the plant-specific transcriptional regulators, LATERAL ORGAN BOUNDARIES-DOMAIN16/ASYMMETRIC LEAVES2-LIKE 18 (LBD16/ASL18) and LBD29/ASL16. Detailed expression analysis using GFP-tagged LBD16 reporter protein indicated that LBD16-GFP was mainly expressed at the LR initiation sites in three cell files of the xylem pole pericycle of the primary roots. Furthermore, expression of the artificial dominant repressor of LBD16 (LBD16-SRDX) under the control of its own regulatory region completely blocked both the polar nuclear migration and the first ACDs of the xylem pole pericycle cells for LR initiation. Taken together, these results indicate that the localized activity of auxin-inducible LBD/ASL proteins links to the regulation of ACDs necessary for LR initiation in Arabidopsis.
