Flower development of Phalaenopsis orchid involves functionally divergent SEPALLATA‐like genes

The Phalaenopsis orchid produces complex flowers that are commercially valuable, which has promoted the study of its flower development. E‐class MADS‐box genes, SEPALLATA (SEP), combined with B‐, C‐ and D‐class MADS‐box genes, are involved in various aspects of plant development, such as floral meristem determination, organ identity, fruit maturation, seed formation and plant architecture. Four SEP‐like genes were cloned from Phalaenopsis orchid, and the duplicated PeSEPs were grouped into PeSEP1/3 and PeSEP2/4. All PeSEPs were expressed in all floral organs. PeSEP2 expression was detectable in vegetative tissues. The study of protein–protein interactions suggested that PeSEPs may form higher order complexes with the B‐, C‐, D‐class and AGAMOUS LIKE6‐related MADS‐box proteins to determine floral organ identity. The tepal became a leaf‐like organ when PeSEP3 was silenced by virus‐induced silencing, with alterations in epidermis identity and contents of anthocyanin and chlorophyll. Silencing of PeSEP2 had minor effects on the floral phenotype. Silencing of the E‐class genes PeSEP2 and PeSEP3 resulted in the downregulation of B‐class PeMADS2‐6 genes, which indicates an association of PeSEP functions and B‐class gene expression. These findings reveal the important roles of PeSEP in Phalaenopsis floral organ formation throughout the developmental process by the formation of various multiple protein complexes.