TCP transcription factors control the morphology of shoot lateral organs via negative regulation of the expression of boundary-specific genes in Arabidopsis

Plants form shoot meristems in the so-called boundary region, and these meristems are necessary for normal morphogenesis of aerial parts of plants. However, the molecular mechanisms that regulate the formation of shoot meristems are not fully understood. We report here that expression of a chimeric repressor from TCP3 (TCP3SRDX), a member of TEOSINTE BRANCHED1, CYCLOIDEA, and PCF (TCP) transcription factors in Arabidopsis thaliana, resulted in the formation of ectopic shoots on cotyledons and various defects in organ development. Expression of TCP3SRDX induced ectopic expression of boundary-specific genes, namely the CUP-SHAPED COTYLEDON (CUC) genes, and suppressed the expression of miR164, whose product cleaves the transcripts of CUC genes. This abnormal phenotype was substantially reversed on the cuc1 mutant background. By contrast, gain of function of TCP3 suppressed the expression of CUC genes and resulted in the fusion of cotyledons and defects in formation of shoots. The pattern of expression of TCP3 did not overlap with that of the CUC genes. In addition, we found that eight TCPs had functions similar to that of TCP3. Our results demonstrate that the TCP transcription factors play a pivotal role in the control of morphogenesis of shoot organs by negatively regulating the expression of boundary-specific genes.