Molecular Mechanism Controlling Floral Symmetry In Leguminosae

Momosymmetric flowers are thought to be evolved from ancestral groups with radiallysymmetric flowers. In snapdragon (Antirrhinum majus), two genes play a key role in thedevelopment of dorsoventral asymmetry: Cycliodea (Cyc) and Dichotoma (Dich). Both Cycand Dich belong to a TCP domain gene family Cyc and Dich orthologs have been found inclose relatives of Antirrhinum, such as toadflax, but it is still unknown whether Cyc–like genescontrol the floral symmetry in more distantly related plants. In this study, we addressed thisquestion by investigating the floral development in Leguminosae, particularly in a modellegume plant, Lotus japonicus. Our current work has shown that Cyc-like genes are involved incontrolling both flower asymmetry and inflorescence architecture in Papilionoidea .Eleven orthologs of Cyc and Dich were isolated from Lotus japonicus, Glycine Max andPisum sativa. Sequence analysis indicates that all them belong to CYC/TB1 subfamily of TCPdomain gene with TCP domain and R region. Two orthologs of Cyc , Ljcyc1 and Ljcyc2, fromLotus japonicus were focused since the transgentic plants are easy to be obtained in Lotusjaponicus and they are higher similarity to Cyc than others. Ljcyc1 encodes a deduced proteincontaining 370 amino acids, with 39% identity and 42.6% similarity to CYC. A proteincontaining 370 amino acids is deduced from Ljcyc2 sequence, which is 41.8% identical and46.3% similar to CYC protein.Ljcyc2 shares the similar asymmetry expression pattern as Cyc in Antirrhinum majusduring the floral primordia development. The lateral petals obtained dorsal identity in theLjcyc2 ectopic expression transgenic lines, while ventrolized lateral petals are observed inLjcyc2 antisense transgenic lines. All these data demonstrates Ljcyc2 gene is recruited tocontrol floral symmetry in Lotus japonicus. Ljcyc2 mRNA was also detected in the shoot apicalmeristems and inflorescence primordia. The phenotypes of antisense Ljcyc2 transgenicclarified its function of controlling the architecture of inflorescence. The similar expression pattern of Ljcyc1 is also found during floral bud development.But during the flower inflorescence initiation, the expression regions of Ljcyc1 are located onthe SAM, while Ljcyc2 expresses between the boundary of secondary inflorescence and SAM.In the Ljcyc1 antisense transgenic lines, the number of flower organs increased and shape oflateral and ventral petals became symmetric, which indicates Ljcyc1 involves in the control offlower asymmetry by reducing flower organs and controlling individual organ shape.