Abstract
CUP-SHAPED COTYLEDON1 (CUC1) and CUC2 , functionally redundant genes of Arabidopsis, promote shoot apical meristem (SAM) formation through the activation of the knox-type homeobox gene SHOOT MERISTEMLESS (STM). They also play important roles in boundary formation of shoot organs such as cotyledons or some floral organs.Through microarray experiments, we identified the BELL-type homeobox gene PENNYWISE (PNY) as a gene upregulated by overexpression of CUC1 in cotyledons. The PNY protein has been shown to participate in SAM maintenance through physically interacting with STM. CUC1 overexpression promotes PNY expression even in the absence of STM activity, suggesting that the activation of PNY by CUC1 occurs independently of STM. In flowers, the pny mutant shows weak defects in sepal separation and septum formation. Significantly, these phenotypes are greatly enhanced by cuc1 or cuc2 mutations. These results indicate that CUC1, CUC2 and PNY together function in normal sepal and septum development.
