Poster: Evolution

Abs # 796: Using synthetic gene cluster technology to model concerted evolution of the Arabidopsis thaliana RBCSB locus

Presenter:	Jelesko, John G, jelesko@vt.edu
Authors	Jelesko, John G (A)   Thompson, Whitney  (A)   Carter, Kristy  (A)   Furuya, Masaki  (C)   Gruissem, Wilhelm  (B)
Affiliations:	(A): Virginia Tech (B): ETH, Zurich, Switzerland (C): Hitachi Advanced Research Laboratories, Hatoyama, Japan

Concerted evolution is the process whereby paralogous genes organized as a gene cluster can rapidly evolve by recombination between misaligned paralogs leading to reciprocal recombinant genes, deletions, and gene duplications. To model both the frequency and character of unequal crossing-over within a small gene cluster, we utilized transgenic Arabidopsis plants containing a synthetic RBCSB gene cluster that enables the detection of rare meiotic unequal crossover events using bioluminescence (Jelesko, J., et al. 1999, PNAS USA, 96:10302). Eight F2 populations derived from F1 hemizygous lines containing the synthRBCSB1 gene cluster showed luciferase positive F2 plants at a frequency of 1-3 x 10^-6, indicating that unequal crossing-over between sister chromatids was rare, but reproducible at two different transgenic loci. High resolution mapping of the recombination resolution sites showed a non-uniform distribution of recombination resolution sites. About half of the mapped resolution sites correlated with a simple model of recombination resolution correlating with the length of sequence identity. However, the other mapped resolution sites did not. Instead, these other resolution sites showed a pattern that suggests recombination resolution was determined by a transition from a region of relatively high sequence similarity to a region of relatively low sequence similarly. The RBCS3B/1B chimeric genes also showed suppression of expected gene conversion tracts frequently associated with crossovers between homologous chromosomes. These results are reminiscent of restrictions in intrachromatid exchange reported in yeast. These results provide several new insights into how the details of meiotic unequal crossing-over affect the concerted evolution of gene clusters.