CONTROL OF ROOT-GROWTH AND DEVELOPMENT BY CYCLIN EXPRESSION

ROOT development is plastic, with post-embryonic organogenesis being m ediated by meristems(1), Although cell division is intrinsic to merist em initiation, maintenance and proliferative growth, the role of the c ell cycle in regulating growth and development is unclear, To address this question, we examined the expression of cdc2 and eye genes, which encode the catalytic and regulatory subunits, respectively, of cyclin -dependent protein kinases that control progression through the cell c ycle(2). Unlike cdc2, which is expressed not only in apical meristems but also before lateral root initiation(3) in quiescent, pericycle cel ls arrested in the G2 phase of the cell cycle(4), cyc1At transcripts a ccumulate specifically in dividing cells immediately before cytokinesi s. Ectopic expression of cyc1At under the control of the cdc2aAt promo ter in Arabidopsis plants markedly accelerates growth without altering the pattern of lateral root development or inducing neoplasia. Thus c yclin expression is a limiting factor for growth, which in turn drives indeterminate development of the root system.