A generalized least-squares estimate for the origin of sporophytic self-incompatibility.
Analysis of nucleotide sequences that regulate the expression of self-incompatibility in flowering plants affords a direct means of examining classical hypotheses for the origin and evolution of this major feature of mating systems. Departing from the classical view of monophyly of all forms of self-incompatibility, the current paradigm for the origin of self-incompatibility postulates multiple episodes of recruitment and modification of preexisting genes. In Brassica, the S locus, which regulates sporophytic self-incompatibility, shows homology to a multigene family present both in self-compatible congeners and in groups for which this form of self-incompatibility is atypical. A phylogenetic analysis of S-allele sequences together with homologous sequences that do not cosegregate with self-incompatibility permits dating the change of function that marked the origin of self-incompatibility. A generalized least-squares method is introduced that provides closed-form expressions for estimates and standard errors for function-specific divergence rates and times of divergence among sequences. This analysis suggests that the age of the sporophytic self-incompatibility system expressed in Brassica exceeds species divergence within the genus by four- to fivefold. The extraordinarily high levels of sequence diversity exhibited by S alleles appears to reflect their ancient derivation, with the alternative hypothesis of hypermutability rejected by the analysis.
Uyenoyama
M K
MK
Department of Zoology, Duke University, Durham, North Carolina 27708-0325, USA.
D000483:Alleles; D005075:Biological Evolution; D001937:Brassica / Q000235:genetics / Q000502:physiology*; D017343:Genes, Plant; D014644:Genetic Variation / Q000235:genetics; D016018:Least-Squares Analysis; D005810:Multigene Family / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics; D012098:Reproduction
D010940:Plant Proteins; D011494:Protein Kinases; C079832:S-receptor kinase