The MADS-box gene DEFH28 from Antirrhinum is involved in the regulation offloral meristem identity and fruit development

DEFH28 is a novel MADS-box gene from Antirrhinum majus. Phylogenetic recons truction indicates that it belongs to the SQUA-subfamily of MADS-box genes, Based on its expression pattern and the phenotype of transgenic plants it is predicted that DEFH28 exerts a dual function during flower development, namely control of meristem identity and fruit development. Firstly, DEFH28 is expressed in the inflorescence apical meristem and might control, togeth er with SQUAMOSA (SQUA), floral meristem identity in Antirrhinum. Also, DEF H28 is sufficient to switch inflorescence shoot meristem to a floral fate i n transgenic Arabidopsis thaliana plants. Secondly, DEFH28 is expressed in carpel walls, where it may regulate carpel wall differentiation and fruit m aturation. Support for this later role comes from overexpression of DEFH28 throughout the silique in transgenic Arabidopsis plants where it altered th e identity of the replum and valve margin cells so that they adopted a valv e cell identity. This late aspect of the DEFH28 function is identical to th e FRUITFULL (FUL) function of Arabidopsis as demonstrated in gain-of-functi on plants. FUL, like DEFH28, belongs to the SQUA-subfamily of MADS-box gene s. DEFH28 most likely represents the ortholog of FUL. Promoter analysis sho ws that the control mechanism conferring a carpel wall specific expression has been conserved between Antirrhinum and Arabidopsis during evolution. Al though the overall flower development between Antirrhinum and Arabidopsis i s very similar, their carpels mature into different types of fruits: capsul es and siliques, respectively. Therefore, it is suggested that the role of DEFH28 in control of carpel wall differentiation reflects a conserved molec ular mechanism integrated into two very different carpel developmental path ways.