A SEPALLATA1-like gene of Isatis indigotica Fort. regulates flowering time and specifies floral organs.

An orthologous gene of SEPALLATA1, designated as IiSEP1, was isolated from Isatis indigotica. The genomic DNA of IiSEP1 is 3.1 Kb in length. The full-length cDNA of IiSEP1 is 1481 bp and contains a 756 bp ORF encoding a 251-amino-acid protein. Sequence comparison revealed that IiSEP1 belonged to the MADS-box gene family. IiSEP1 contains 7 exons and 6 introns, showing similar exon-intron structure with Arabidopsis SEP1. Phylogenetic analysis suggested that IiSEP1 belonged to AGL2/SEP subfamily and was likely to be an I. indigotica ortholog of Arabidopsis SEP1. Quantitative real-time PCR showed that IiSEP1 was predominantly expressed in the reproductive organs. Ectopic expression of IiSEP1 in Arabidopsis resulted in early flowering, accompanied with the reduction of inflorescence number and the production of terminal flower on the top of the main stems. Moreover, IiSEP1 overexpressing flowers generated numerous variations in phenotype. The sepals were changed into petal-sepal mosaic structures or displayed carpelloid features, and transparent ovules were formed in internal surface of these sepals. In addition, some flowers were constituted by sepals and pistil, but lacked petals and stamens. Taken together, IiSEP1 might play important roles in reproductive growth of I. indigotica and could affect the morphogenesis of flowers and fruits.