Fig. 6. A model for control of CUC gene expression in the embryo. (A,B) Diagrams indicating regulatory events in the cotyledon boundary region of an early heart stage embryo for CUC1 (A) and CUC2 (B). The arrows represent direct or indirect interactions. CUC1 and CUC2 are redundantly required to activate STM (Aida et al., 1999; Hibara et al., 2003; Takada et al., 2001). STM in turn is required for proper CUC1 and CUC2 expression (Aida et al., 1999; Aida et al., 2002; Kwon et al., 2005) (this study). AtBRM is a positive regulator of both CUC1 and CUC2, while SYD is required for CUC2 expression. Based on our phenotypical and molecular analyses, AtBRM and SYD are not likely to act in the STM pathway.