Do plants have more genes than humans? Yes, when it comes to ABC proteins

Abstract

Joachim Messing in his recent ‘Comment’ 1 Messing J. Do plants have more genes than humans?. Trends Plant Sci. 2001; 6: 195-196 Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar discussed the remarkable similarity in gene count between the human 2 International Human Genome Sequencing ConsortiumInitial sequencing and analysis of the human genome. Nature. 2001; 409: 860-921 Crossref PubMed Scopus (17490) Google Scholar , 3 Venter C.J. et al. The sequence of the human genome. Science. 2001; 291: 1304-1351 Crossref PubMed Scopus (10466) Google Scholar and Arabidopsis thaliana genomes 4 Arabidopsis Genome InitiativeAnalysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature. 2000; 408: 796-815 Crossref PubMed Scopus (7054) Google Scholar . No one knows why the number of open-reading-frames (ORFs) in the Arabidopsis genome (25 500) 4 Arabidopsis Genome InitiativeAnalysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature. 2000; 408: 796-815 Crossref PubMed Scopus (7054) Google Scholar is only slightly less than that estimated for the human genome (31 500) 2 International Human Genome Sequencing ConsortiumInitial sequencing and analysis of the human genome. Nature. 2001; 409: 860-921 Crossref PubMed Scopus (17490) Google Scholar , 3 Venter C.J. et al. The sequence of the human genome. Science. 2001; 291: 1304-1351 Crossref PubMed Scopus (10466) Google Scholar – specifically, how humans can get by with so few genes – but we can answer Messing's opening question ‘Do plants have more genes than humans?’ in the affirmative in at least some cases. The ATP-binding cassette (ABC) proteins are a case in point, many of which are modularly constructed membrane proteins containing idiotypic nucleotide-binding folds (NBFs). By compiling the first complete inventory of the ABC protein superfamily from Arabidopsis 5 Sánchez-Fernández, R. et al. The Arabidopsis thaliana ABC protein superfamily: a complete inventory. J. Biol. Chem. 10.1074/jbc.M103104200 (www.jbc.org/) Google Scholar (http://www.arabidopsisabc.net)– the first complete inventory of ABC proteins from any multicellular organism – we have determined that the genome of this plant encodes 129 ABC proteins, which fall into 13 subfamilies (Fig. 1). This gene count far outstrips those for the human genome and for any other animal genome sequenced to date. The human genome is estimated to encode a mere 51 ABC proteins (http://www.humanabc.org); those of Caenorhabditis elegans (19 000 ORFs; http://www.proteome.com/databases/WormPD/WormPDsearch-long.html) and Drosophila melanogaster (13 600 ORFs; http://www.flybase.bio.indiana.edu/) only 58 and 55, respectively.