THE EVOLUTION OF PLANT NUCLEAR GENES

We analyze the evolutionary dynamics of three of the best-studied plan t nuclear multigene families, The data analyzed derive from the genes that encode the small subunit of ribulose-1,5-bisphosphate carboxylase (rbcS), the gene family that encodes the enzyme chalcone synthase (Ch s), and the gene family that encodes alcohol dehydrogenases (Adh), In addition, we consider the limited evolutionary data available on plant transposable elements, New Chs and rbcS genes appear to be recruited at about 10 times the rate estimated for Adh genes, and this is correl ated with a much smaller average gene family size for Adh genes, In ad dition, duplication and divergence in function appears to be relativel y common for Chs genes in flowering plant evolution, Analyses of synon ymous nucleotide substitution rates for Adh genes in monocots reject a linear relationship with clock time, Replacement substitution rates v ary with time in a complex fashion, which suggests that adaptive evolu tion has played an important role in driving divergence following gene duplication events, Molecular population genetic studies of Adh and C hs genes reveal high levels of molecular diversity within species, The se studies also reveal that inter- and intralocus recombination are im portant forces in the generation allelic novelties, Moreover, illegiti mate recombination events appear to be an important factor in transpos able element loss in plants, When we consider the recruitment and loss of new gene copies, the generation of allelic diversity within plant species, and ectopic exchange among transposable elements, we conclude that re combination is a pervasive force at all levels of plant evolu tion.