The rooted maximum-likelihood phylogenetic tree of OPR family genes from eleven representative species. The rooted maximum-likelihood (ML) phylogenetic tree of OPR genes in eleven representative plants was inferred from the amino acid sequence alignments of the Oxidored_FMN domain (Additional file 3) under the Jones-Taylor-Thornton (JTT) model, implemented in Phylip v3.68 package. The old yellow enzyme 1 (OYE1) of Saccharomyces cerevisiae (ScOYE1) was selected as an out of group marker and its accession number in SWISS-PROT is Q02899. The bootstrap values from 1000 resamplings are given at each node and the branch lengths are drawn to scale. The seven conserved OPR subfamilies are represented as Sub.I, II, III, IV, V, VI and VII at the right side of the ML tree.