Abstract
MIKCc-type MADS-box genes encode transcription factors that control floral organ morphogenesis and flowering time in flowering plants. Here, in order to determine when the subfamilies of MIKCc originated and their early evolutionary trajectory, we sampled and analyzed the genomes and large-scale transcriptomes representing all the orders of gymnosperms and basal angiosperms. Through phylogenetic inference, the MIKCc-type MADS-box genes were subdivided into 14 monophyletic clades. Among them, the gymnosperm orthologs of AGL6, SEP, AP1, GMADS, SOC1, AGL32, AP3/PI, SVP, AGL15, ANR1, and AG were identified. We identified and characterized the origin of a novel subfamily GMADS within gymnosperms but lost orthologs in monocots and Brassicaceae. ABCE model prototype genes were relatively conserved in terms of gene number in gymnosperms, but expanded in angiosperms, whereas SVP, SOC1, and GMADS had dramatic expansions in gymnosperms but conserved in angiosperms. Our results provided the most detailed evolutionary history of all MIKCc gene clades in gymnosperms and angiosperms. We proposed that although the near complete set of MIKCc genes had evolved in gymnosperms, the duplication and expressional transition of ABCE model MIKCc genes in the ancestor of angiosperms triggered the first flower.
Highlights
MADS-box genes encode a family of transcription factors (TFs) that have fundamental roles in controlling the development in plants, animals, and fungi (Becker et al, 2000)
Because determining the phylogenetic relationship of this novel clade with other MADS-box genes was difficult and its lack of name, we proposed to name this clade of genes as GMADS for its significant expansion in gymnosperms
The major MIKCc-type MADS-box genes were characterized and we identified a new clade GMADS
Summary
MADS-box genes encode a family of transcription factors (TFs) that have fundamental roles in controlling the development in plants, animals, and fungi (Becker et al, 2000). MIKCc genes are concisely studied in expression patterns or mutant phenotypes and best known for their functions (Becker and Theißen, 2003), especially in flowering plants that work as floral organ identity genes. These floral organ identity MIKCc-type MADS-box genes have been subdivided into the following four classes: A, B, C, and E genes that provide five different homeotic functions, with A specifying sepals, A+B+E for petals, B+C+E for stamens, C+E for carpels, and D (sister of C genes) for ovules (Angenent and Colombo, 1991; Weigel and Meyerowitz, 1994)
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