Final Activity Report Summary - ROOTINIT (Stem cell maintenance and reactivation in lateral root initiation)
The correct integration of cell division in growth and development requires sensing of developmental and physiological signals by the cell cycle machinery. Proliferating cells in roots are concentrated at the root tip in meristems and are spatially separated from elongated non-dividing tissues. Specific tissues, such as the pericycle, maintain the capacity to reactivate division under hormonal stimulation and to form de novo lateral root meristems. D-type cyclins can stimulate entry into the mitotic cell cycle and respond to sucrose and plant hormones. Expressing d-type cyclin 2;1 (CYCD2;1) throughout the root meristem triggers cell division, as noted by Qi and John, 2007, but its function in root apical meristems remains enigmatic.
In this project we showed that CYCD2;1 was induced by sucrose and was present in all meristematic tissues in the root apex. However, the intracellular distribution of CYCD2;1 was variable, as cells in regions marked by auxin maxima did not accumulate CYCD2;1 in the nucleus. The concentration of CYCD2;1 in the nucleus was dependent on kip-related protein 2 (KRP2), and KRP2 turnover itself was under auxin control. Furthermore, we demonstrated that CYCD2;1 contributed to the reactivation of pericycle cells by auxin. These results indicated that KRP2 sequestered CYCD2;1 in the nucleus and that CYCD2;1 activity stimulated auxin induced cell division in the pericycle integrating sucrose and auxin sensing, revealing an additional control mechanism for cell cycle regulation in the pericycle.
In this project we showed that CYCD2;1 was induced by sucrose and was present in all meristematic tissues in the root apex. However, the intracellular distribution of CYCD2;1 was variable, as cells in regions marked by auxin maxima did not accumulate CYCD2;1 in the nucleus. The concentration of CYCD2;1 in the nucleus was dependent on kip-related protein 2 (KRP2), and KRP2 turnover itself was under auxin control. Furthermore, we demonstrated that CYCD2;1 contributed to the reactivation of pericycle cells by auxin. These results indicated that KRP2 sequestered CYCD2;1 in the nucleus and that CYCD2;1 activity stimulated auxin induced cell division in the pericycle integrating sucrose and auxin sensing, revealing an additional control mechanism for cell cycle regulation in the pericycle.