In Arabidopsis, the closely related APETALA1 (APT) and CAULIFLOWER (CAL) MA
DS-box genes share overlapping roles in promoting flower meristem identity.
Later in flower development, the AP1 gene is required for normal developme
nt of sepals and petals. Studies of MADS-domain proteins in diverse species
have shown that they often function as heterodimers or in larger ternary c
omplexes, suggesting that additional proteins may interact with AP1 and CAL
during flower development. To identify proteins that may interact with AP1
and CAL, we used the yeast two-hybrid assay. Among the five MADS-box genes
identified in this screen, the SEPALLATA3 (SEP3) gene was chosen for furth
er study. Mutations in the SEP3 gene, as well as SEP3 antisense plants that
have a reduction in SEP3 RNA, display phenotypes that closely resemble int
ermediate alleles of APT. Furthermore, the early flowering phenotype of pla
nts constitutively expressing AP1 is significantly enhanced by constitutive
SEP3 expression. Taken together, these studies suggest that SEP3 interacts
with AP1 to promote normal flower development.