Rab23 is monophyletic and restricted to organisms with conventional flagella. (A) Percent identity of Rab23 homologues. T-coffee was used to produce an alignment of Rab23 sequences using default parameters. A table of percent identities was generated using the alignment http://imed.med.ucm.es/Tools/sias.html. Species abbreviations: Hs = Homo sapiens, Xt = Xenopus tropicalis, Dm = Drosophila melanogaster, Mb = Monosiga brevicolli, Cr = Chlamydomonas reinhardtii, Tb = Trypanosoma brucei, Tc = Trypanosoma cruzi, Lm = Leishmania major, Ng = Naegleria gruberi, Tv = Trichomonas vaginalis, Pr = Phytophthora ramorum and Tg = Toxoplasma gondii. (B) Phylogenetic reconstruction of Rab5, Rab7, Rab23 and Rab28 families from eukaryotes in the major sampled supergroups. Rab23 robustly forms a separate clade with Bayesian posterior probability support values greater than 0.95 denoted by a vertical bar next to the clade. Rab5 and Rab7 were included in the analysis as outgroups and subclade support values are not shown. Rab7 was used to root the tree. Circles above nodes indicate statistical support for MrBayes/PhyML 0.99/95 (posteriorprobability/bootstrap, respectively). Those nodes supported by both methods, but with lower support values are written above the node. The diversity of eukaryotic supergroups within each family is illustrated by color-coded taxon names. Species abbreviations: Hs = Homo sapiens, Xt = Xenopus tropicalis, Dm = Drosophila melanogaster, Ce = Caenorhabditis elegans, Mb = Monosiga brevicolli, Sc = Saccharomyces cerevisiae, Cn = Cryptococcus neoformans, Ro = Rhizopus oryzae, At = Arabidopsis thaliana, Cr = Chlamydomonas reinhardtii, Ot = Ostreococcus tauri, Cm = Cyanidioschyzon merolae, Tb = Trypanosoma brucei, Tc = Trypanosoma cruzi, Lm = Leishmania major, Gl = Giardia lamblia, Ng = Naegleria gruberi, Tv = Trichomonas vaginalis, Pr = Phytophthora ramorum, Pf = Plasmodium falciparum, Tt = Tetrahymena thermophila, Tg = Toxoplasma gondii, Tp = Thalassiosira pseudonana, Dd = Dictyostelium discoideum and Eh = Entamoeba histolytica. (C) Distribution of Rab23 homologues among flagellates and non-flagellates. Correlation between possession of a motile flagellum exhibiting a 9+2 microtubule arrangement and a Rab23 orthologue was found. Data suggest that Rab23 is not found in taxa lacking motile flagella or with non-conventional flagellar assembly, i.e. P. falciparum and G. lamblia.