Cells and domains: Two views of the shoot meristem in Arabidopsis

All aerial parts of a plant are generated by groups of dividing cells called shoot meristems. These structures determine the arrangement and number of the different organs they produce, and, as a consequence the architecture of the plant largely depends on meristem activity. Extensive morphological studies have led to a model which postulates that shoot meristems are organised into functionally and morphologically distinct zones. According to this model, the centre of the meristem is responsible for cell production and meristem maintenance, whereas the periphery will initiate the organ primordia. Recently, genetic analysis allowed the identification of mutants affected in different functions of the meristem and some of the genes involved have now been identified. Meristem function also depends on the strict coordination of morphogenesis at the cellular level, as illustrated by the highly ordered patterns of cell division, division plane alignment and cell expansion observed in many species. Over the past few years, our understanding of the molecular mechanisms that control cell proliferation and growth has progressed significantly. Therefore, we can now start to unravel the networks that link these basic cellular processes to the regulators that control plant development at the level of the whole meristem.