Genome-Wide Characterization of the Isatis indigotica MADS-box Family and Role of IiSVP in Flowering

MADS-box family genes play an important role in the development of plant reproductive growth, but there have been no genome-wide characterization reports on Isatis indigotica Fortune. In this study, eighty IiMADS genes were identified and clustered into 16 subgroups (3 type I and 13 type II) with reference to Arabidopsis MADS genes. Most IiMADS proteins in the same cluster had similar exon-intron and motif structures. Seventy-four IiMADS genes were randomly distributed among 7 chromosomes, and the remaining genes were contigs. The RNA-seq data showed that most IiMADS transcripts were highly enriched in roots, stems, flowers and fruits but rarely in leaves. Based on our phylogenetic and expression analyses, the IiSVP gene from I. indigotica was cloned and functionally characterized. qRT-PCR revealed that IiSVP is mainly expressed in stems, buds, flowers, and fruits. The IiSVP protein could interact with IiSOC1 and IiFLC, which was detected by BiFC and Y2H. The heterogeneous overexpression of IiSVP in Arabidopsis showed that it suppresses floral organ development, delays flowering and is significantly related to the expression of flowering genes such as FLC, SOC1 and GA20ox2. This study provided new information on the MADS family in I. indigotica and suggested that IiSVP is a key gene in suppressing flowering in I. indigotica.