ROLE OF THE ZWILLE GENE IN THE REGULATION OF CENTRAL SHOOT MERISTEM CELL FATE DURING ARABIDOPSIS EMBRYOGENESIS

Postembryonic development in higher plants is marked by repetitive org an formation via a self-perpetuating stem cell system, the shoot meris tem, Organs are initiated at the shoot meristem periphery, while a cen tral zone harbors the stem cells. Here we show by genetic and molecula r analyses that the ZWILLE (ZLL) gene is specifically required to esta blish the central-peripheral organization of the embryo apex and that this step is critical for shoot meristem self-perpetuation. zll mutant s correctly initiate expression of the shoot meristem-specific gene SH OOT MERISTEMLESS in early embryos, but fail to regulate its spatial ex pression pattern at later embryo stages and initiate differentiated st ructures in place of stem cells, We isolated the ZLL gene by map-based cloning. It encodes a novel protein, and related sequences are highly conserved in multicellular plants and animals but are absent from bac teria and yeast. We propose that ZLL relays positional information req uired to maintain stem cells of the developing shoot meristem in an un differentiated state during the transition from embryonic development to repetitive postembryonic organ formation.