Doubled In The Americas Allotetraploid Wild Rice Gene Evolution And Expression Differences

Polyploidization has been an important driving force in plant evolution;about 70 percent of higher plants have experienced polyploidization once or more in their evolutionary history.The direct result of polyploidization is duplication of gene or genome.Using three allopolyploids Oryza species with CD genome:O.alta Swallen,O.grandiglumis(Doell) Prod and O.latifolia Desv as testing materials,the molecular evolution of duplicated genes was performed by DNA sequencing and gene expression analysis in the present study in order to understand how the duplicate genes experienced mutual adaption and coordinated evolution in polyploidy.The main results were summarized as follows:1.The evolution of nucleotide sequence of the duplicated genes in the allopolyploids In this work,three lower-copy nuclear genes located in different chromosomes,i.e.leafy hull serilel gene(Lhs1),granule-bound srarch synthase gene(GBSS-Waxy) and granule-binding starch synthaseⅡgene(GbssⅡ) were selected as target genes.Low nucleotide diversity(θw) ranging from 0.0005 to 0.0048 was found by analyzing the nucleotide sequences of the three genes in 15 samples from three allopoliploidy species.In addition,there were different levels of nucleotide diversity of the C and D genome in intra-specific,inter-specific of the allopolyploid species and even in different genes.Specifically,the nucleotide diversity of Lhs1 gene in C genome was lower than that in D genome of all the three species,especially those of the Waxy gene in C genome of O.grandiglumis is twice as large as that in D genome of O.latifolia species; and those of the GbssⅡgene in C and D geneme of O.alta and O.latifolia species were nearly the same,but in the species O.grandiglumis the nucleotide diversity in C genome was twice more than that of the D genome.Based on the algorithm of Hudson and Kaplan,the minimum number of historical recombination events was not found in the other species except for the C genome in the O.latifolia species. Several statistical tests were used to test the hypothesis that three nuclear genes had been evolving in accordance with expectation under neutral theory.The significant departure from neutrality was found in C or D genome of some species in Lhs1 gene and Waxy gene by Fu and Li'D test.But that was not found in the other tests.2.Differential express of the duplicated genes in allopolyploidsIn order to estimate the expression patterns and levels of the duplicated genes in the allopolyploids by cDNA-SSCP technique,5 pairs of primer were designed to be used for reverse transcription based on the nucleotide sequences of three genes as well as other two nuclear genes. Our results revealed that genes duplicated by polyploidy contributed unequally to the tanscriptome.The expression levels of homologous genes from different genes,species and even different samples under the same species varied.The gene silencing of Adh1 and GbssⅡgene in D genome was detected separately in the samples 101405 of the species O.grandiglumis and 105557 of the species O.latifolia.It should be noted that this form of silencing can be genome specific rather than species specific.Moreover this phenomenon was in accordance with their sequence information.