Abstract
In plants, most shoot organs are derived from the shoot apical meristem (SAM), which is formed between cotyledon primordia during embryogenesis. The Arabidopsis genes CUP-SHAPED COTYLEDON1 (CUC1), CUC2 and CUC3 encoding NAC transcriptional activators regulate SAM formation and morphogenesis of shoot organ boundaries. We have identified a number of candidate downstream genes whose expression is positively controlled by CUC genes during embryogenesis. To investigate their functions, we expressed each candidate under the CUC2 promoter in cuc1 cuc2 embryos, which develop fused cotyledons and fail to form a SAM. Two of them were able to rescue the phenotype, resulting in formation of partially separated cotyledons and a functional SAM. Moreover, the two genes also affected formation of sepal boundaries, another location that required CUC gene activity for proper morphogenesis. These results indicate that the two genes act downstream of CUC1 and CUC2 and promote development of SAM and shoot organ boundaries.
