title: An S-RNase-based gametophytic self-incompatibility system evolved only once in eudicots.
abstract: It has been argued that the common ancestor of about 75% of all dicots possessed an S-RNase-based gametophytic self-incompatibility (GSI) system. S-RNase genes should thus be found in most plant families showing GSI. The S-RNase gene (or a duplicate) may also acquire a new function and thus genes belonging to the S-RNase lineage may also persist in plant families without GSI. Nevertheless, sequences that belong to the S-RNase lineage have been found in the Solanaceae, Scrophulariaceae, Rosaceae, Cucurbitaceae, and Fabaceae plant families only. Here we search for new sequences that may belong to the S-RNase lineage, using both a phylogenetic and a much faster and simpler amino acid pattern-based approach. We show that the two methods have an apparently similar false-negative rate of discovery (approximately 10%). The amino acid pattern-based approach produces about 15% false positives. Genes belonging to the S-RNase lineage are found in three new plant families, namely, the Rubiaceae, Euphorbiaceae, and Malvaceae. Acquisition of a new function by genes belonging to the S-RNase lineage is shown to be a frequent event. A putative S-RNase sequence is identified in Lotus, a plant genus for which molecular studies on GSI are lacking. The hypothesis of a single origin for S-RNase-based GSI (before the split of the Asteridae and Rosidae) is further supported by the finding of genes belonging to the S-RNase lineage in some of the oldest lineages of the Asteridae and Rosidae, and by Baysean constrained tree analyses.
authors.affiliation: Molecular Evolution Group, Instituto de Biologia Celular e Molecular (IBMC), University of Porto, Rua do Campo Alegre 823, 4150-180, Porto, Portugal.
authors.forename: Jorge
authors.initials: J
authors.lastname: Vieira
authors.forename: Nuno A
authors.initials: NA
authors.lastname: Fonseca
authors.forename: Cristina P
authors.initials: CP
authors.lastname: Vieira
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D005075:Biological Evolution; D020134:Catalytic Domain; D017124:Conserved Sequence; D030562:Databases, Protein; D008969:Molecular Sequence Data; D010802:Phylogeny; D018521:Plant Physiological Phenomena; D012260:Ribonucleases / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D000596:Amino Acids; D012260:Ribonucleases; C022542:ribonuclease S