Phylogenomic Synteny Network Analysis of MADS-Box Transcription Factor Genes Reveals Lineage-Specific Transpositions, Ancient Tandem Duplications, and Deep Positional Conservation

Conserved genomic context provides critical information for comparative evolutionary analysis. 29 With the increase in numbers of sequenced plant genomes, synteny analysis can provide new 30 insight into gene family evolution. Here, we exploit a network analysis approach to organize and31 interpret massive pairwise syntenic relationships. Specifically, we analyzed synteny networks of 32 the MADS-box transcription factor gene family using fifty-one completed plant genomes. In 33 combination with phylogenetic profiling, several novel evolutionary patterns were inferred and 34 visualized from synteny network clusters. We found lineage-specific clusters that derive from 35 transposition events for the regulators of floral development (APETALA3 and PI) and flowering36 time (FLC) in the Brassicales and for the regulators of root-development (AGL17) in Poales. We 37 also identified two large gene clusters that jointly encompass many key phenotypic regulatory 38 Type II MADS-box gene clades (SEP1, SQUA, TM8, SEP3, FLC, AGL6 and TM3). Gene39 clustering and gene trees support the idea that these genes are derived from an ancient tandem 40 gene duplication that likely predates the radiation of the seed plants and then expanded by 41 subsequent polyploidy events. We also identified angiosperm-wide conservation of synteny of 42 several other less studied clades. Combined, these findings provide new hypotheses for the43 genomic origins, biological conservation and divergence of MADS-box gene family members