title: Convergent evolution of RFX transcription factors and ciliary genes predated the origin of metazoans.
abstract: BACKGROUND
  Intraflagellar transport (IFT) genes, which are critical for the development and function of cilia and flagella in metazoans, are tightly regulated by the Regulatory Factor X (RFX) transcription factors (TFs). However, how and when their evolutionary relationship was established remains unknown.
  
  
  RESULTS
  We have identified evidence suggesting that RFX TFs and IFT genes evolved independently and their evolution converged before the first appearance of metazoans. Both ciliary genes and RFX TFs exist in all metazoans as well as some unicellular eukaryotes. However, while RFX TFs and IFT genes are found simultaneously in all sequenced metazoan genomes, RFX TFs do not co-exist with IFT genes in most pre-metazoans and thus do not regulate them in these organisms. For example, neither the budding yeast nor the fission yeast possesses cilia although both have well-defined RFX TFs. Conversely, most unicellular eukaryotes, including the green alga Chlamydomonas reinhardtii, have typical cilia and well conserved IFT genes but lack RFX TFs. Outside of metazoans, RFX TFs and IFT genes co-exist only in choanoflagellates including M. brevicollis, and only one fungus Allomyces macrogynus of the 51 sequenced fungus genomes. M. brevicollis has two putative RFX genes and a full complement of ciliary genes.
  
  
  CONCLUSIONS
  The evolution of RFX TFs and IFT genes were independent in pre-metazoans. We propose that their convergence in evolution, or the acquired transcriptional regulation of IFT genes by RFX TFs, played a pivotal role in the establishment of metazoan.
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada.
authors.forename: Jeffrey S C
authors.initials: JS
authors.lastname: Chu
authors.forename: David L
authors.initials: DL
authors.lastname: Baillie
authors.forename: Nansheng
authors.initials: N
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D002923:Cilia / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D019143:Evolution, Molecular; D006801:Humans; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics*; D000071701:Regulatory Factor X Transcription Factors; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D015800:Protozoan Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors