The molecular basis of auxin-induced cell cycle activation of quiescent cells

Cell cycle regulation is of major importance in plant development. Besides, cell cycle arrest and reactivation play key roles in a variety of processes such as germination, dormancy, lateral root formation, and in response to wounding, pathogen attack and plant hormones. The key regulators of the cell cycle in all eukaryotes are serineheronine protein kinases that are composed of two subunits, a regulatory subunit denoted as cyclin and a catalytic subunit denoted as Cdk (cyclin-dependent protein kinases). In a previous project, we have identified and studied the function of alfalfa cdk and cyclin genes. Studying auxin-stimluated cell cycle reactiovation of differentiated leaf cells, we isolated two different classes of G1 cyclins that become transcriptionally activated in the G0-to-G1 and the G1-to-S transitions, respectively. It is the aim of this project to identify the cis- and trans- acting factors that regulate the expression of these G1 cyclins. Furthermore, we propose to isolate and study novel factors during reentry of quiescent cells into the cell cycle and in the regulation of the G1-to-S transition in cycling cells.