Genome-Wide Identification and Expression Analysis of the MADS-Box Family in Ginkgo biloba

As the most significant transformation stage of plants, the flowering process has typically been the focus of research. MADS-box gene plays an important regulatory role in flower development. In this study, 26 MADS-box genes were identified from Ginkgo biloba, including 10 type-I genes and 16 type-II genes, which were distributed on eight chromosomes. There was no collinearity between the GbMADS genes, and the homology with genes from other species was low. All GbMADS proteins contain conserved MADS domains. The gene structures of GbMADS in the same gene family or subfamily differed, but the conserved protein motifs had similar distributions. The microRNA (miRNA) target sites of the GbMADS genes were predicted. It was found that the expression of 16 GbMADS genes may be regulated by miRNA. The results of cis-acting element analysis showed that the 26 GbMADS genes contained a large number of hormones regulated and light-responsive elements as well as stress-response elements. Furthermore, the quantitative real-time PCR (qRT-PCR) experimental results showed that most GbMADS genes were differentially expressed in the male and female flowers at different developmental stages. Among them, the only MIKC * gene GbMADS16 has the highest expression in the metaphase development of the microstrobilus (M2) stage and is almost not expressed in female flowers. Taken together, these findings suggest that the MADS-box genes may play an important role in the development and differentiation of G. biloba flowers.