Evolutionary processes of PRR genes in angiosperms reconstructed by phylogenetic analysis and syntenic relationships. Chromosomal syntenies among eudicots or monocots were analyzed by the comparative genomic tool, CoGe  or VISTA Browser , and according to previous studies [11, 16–18, 27, 28, 30, 59]. Diamonds and circles indicate gene duplication and gene loss event, respectively. The timing of a gene duplication event that is not clear in the previous studies is shown by dotted line. Black diamonds with a question mark indicate that a gene duplication event derived from a polyploidy event is not resolved. Timings of plant speciation in commelinids, rosids, eurosids I/II and Brassicales are described by broken lines.