Shoot meristems， which harbor a small population of stem cells， are responsible for generating new above-ground organs in plants. The proliferation and differentiation of these stem cells is regulated by a genetic pathway involving two key meristematic genes: () and (). However， it is not well understood how and expression domains in the shoot meristems are specified and maintained during post-embryogenic development. Here， we show that a tomato mutant with fasciated stems， flowers and fruits， due to impaired stem cell activity， is defective in a LITTLE ZIPPER gene denoted as (). DTM forms a negative feedback loop with class III homeodomain-leucine zipper (HD-ZIP III) transcription factors to confine and expression to specific domains of the shoot meristems. Our findings reveal a new layer of complexity in the regulation of plant stem cell homeostasis.