Substitution rates in the X- and Y-linked genes of the plants, Silene latifolia and S. dioica.
Theory predicts that selection should be less effective in the nonrecombining genes of Y-chromosomes, relative to the situation for genes on the other chromosomes, and this should lead to the accumulation of deleterious nonsynonymous substitutions. In addition, synonymous substitution rates may differ between X- and Y-linked genes because of the male-driven evolution effect and also because of actual differences in per-replication mutation rates between the sex chromosomes. Here, we report the first study of synonymous and nonsynonymous substitution rates on plant sex chromosomes. We sequenced two pairs of sex-linked genes, SlX1-SlY1 and SlX4-SlY4, from dioecious Silene latifolia and S. dioica, and their non-sex-linked homologues from nondioecious S. vulgaris and Lychnis flos-jovis, respectively. The rate of nonsynonymous substitutions in the SlY4 gene is significantly higher than that in the SlX4 gene. Silent substitution rates are also significantly higher in both Y-linked genes, compared with their X-linked homologues. The higher nonsynonymous substitution rate in the SlY4 gene is therefore likely to be caused by a mutation rate difference between the sex chromosomes. The difference in silent substitution rates between the SlX4 and SlY4 genes is too great to be explained solely by a higher per-generation mutation rate in males than females. It is thus probably caused by a difference in per-replication mutation rates between the sex chromosomes. This suggests that the local mutation rate can change in a relatively short evolutionary time.
Filatov
Dmitry A
DA
School of Biosciences, University of Birmingham, Edgbaston, United Kingdom. d.filatov@bham.ac.uk
Charlesworth
Deborah
D
D019943:Amino Acid Substitution; D004252:DNA Mutational Analysis; D019143:Evolution, Molecular; D017343:Genes, Plant; D016013:Likelihood Functions; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D029751:Silene / Q000235:genetics*; D014960:X Chromosome; D014998:Y Chromosome