The ROOT MERISTEMLESS1/CADMIUM SENSITIVE2 gene defines a glutathione-dependent pathway involved in initiation and maintenance of cell division duringpostembryonic root development

Activation of cell division in the root apical meristem after germination i s essential for postembryonic root development. Arabidopsis plants homozygo us for a mutation in the ROOT MERISTEMLESS1 (RML1) gene are unable to estab lish an active postembryonic meristem in the root apex, This mutation aboli shes cell division in the root but not in the shoot. We report the molecula r cloning of the RML1 gene, which encodes the first enzyme of glutathione ( GSH) biosynthesis, gamma-glutamylcysteine synthetase, and which is allelic to CADMIUM SENSITIVE2. The phenotype of the rml1 mutant, which was also evi dent in the roots of wild-type Arabidopsis and tobacco treated with an inhi bitor of GSH biosynthesis, could be relieved by applying GSH to rml1 seedli ngs. By using a synchronized tobacco cell suspension culture, we showed tha t the G(1)-to-S phase transition requires an adequate level of GSH, These o bservations suggest the existence of a GSH-dependent developmental pathway essential for initiation and maintenance of cell division during postembryo nic root development.