Abstract
Cell fate separation between the meristem and lateral organs is a central process in plant morphogenesis. CUP-SHAPED COTYLEDON1 (CUC1), a NAC transcription factor, is a key regulator for boundary specification in Arabidopsis thaliana. To investigate the molecular mechanism of boundary establishment, genes acting downstream from CUC1 were screened by transcriptome analyses. Among these genes, LIGHT-DEPENDENT SHORT HYPOCOTYLS 4 (LSH4) encodes a nuclear-localized protein of the ALOG family. LSH4 is expressed in shoot organ boundaries, and its transcription is directly regulated by CUC1. Constitutive expression of LSH4 at the shoot apex resulted in enlargement of the meristem and suppression of leaf primordium growth. In these plants, some sepals have split at the upper part, and ectopic flowers or floral organs are formed within a flower. These results indicate that LSH4 is expressed in the shoot organ boundaries under the direct transcriptional regulation of CUC1, and modulates the cell proliferation and differentiation.
