Systematics and Molecular Evolution of Perennial Soybean Polyploid Complexes

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0089483Doyle and BrownWith his CSIRO-Australia colleague Tony Brown, Jeff Doyle at Cornell University is continuing his highly rated studies on gene markers and genetic consequences of polyploid evolution in the perennial species of soybean, Glycine, related to the cultivated annual G. max. Polyploidy, or whole-chromosome duplication, is common in plants, and especially prevalent among the major crop plants of the world. The 17 named diploid perennial soybeans and their numerous polyploid derivatives are distributed in Australasia and the southeastern Pacific islands, and are extensively represented in the CSIRO soybean germplasm collection. One major goal is to explore in wild species, with genomic tools, ideas about gene silencing and nucleolar dominance formulated from studies on wheat and cabbage polyploids, and to extend such studies to several single- or low-copy nuclear genes, using species complexes where the parent diploids have been identified (and parent tetraploids for hexaploid and octoploid derivatives) and where multiple origins of the "same" polyploid can be documented with molecular markers from both nuclear and chloroplast genomes. Studies of the fate of duplicated (homoeologous) loci will be pursued through cloning of the PCR products, but the investigators are also exploring use of denaturing chromatographic methods to screen numerous polyploid samples for the presence of novel alleles (heteroduplexes from annealing of alleles that differ in length or sequence separate, producing diagnostic elution profiles). Preliminary data are in hand for a nuclear histone gene (H3-D), for nuclear glutamine synthetase, for cox2 (transposed from the mitochondrion in many legumes), and the ribosomal RNA genes. In collaboration with Julie Vogel at DuPont, with access to DuPont's 200,000 soybean cDNA clones, the investigators also plan to screen for candidate nuclear genes showing silencing (through differential hybridization with diploid and polyploid DNAs), and concentrate on those that function in the chloroplast or mitochondrion (and hence where the paternal homoeologue is thought likely to be silenced).