Study On Adaptive Significance Of Transposons Contributing To Gene Evolution In Arabidopsis Thaliana Based On PCR Method

The ubiquitancy of TEs in plant genomes and the important roles in plant genome evolution which TE plays attract people's attention more and more. TEs could cause the evolution of genomes and chromosomes in many ways including insertional mutagenesis, retroposition, chromosomal rearrangenment, gene duplication and service as pivotal sites for ectopic recombination and so on. TEs also have important contribution to the adaptive evolution of genes.We selected 34 ecotypes (including col-0) in Arabidopsis thaliana from different geographical Origins in the world as experiment materials, selected 5 outgroups from Brassica (4) and Arabidopsis arenosa (1) with known divergent time and studied the adaptive significance of TEs congtributing to their host genes. Firstly, we predicted the genes associated with TEs using the available sequenced Arabidopsis thaliana genomes by bioinformatics method and found 2639 gene -TE associations. We selected 7 gene-TE associations according to the functions of genes, length of TEs in genes and the position of TEs in genes. We identified the origins, conservation in genes and the adaptive significance of TEs to genes by studying the presence and absence of TEs associated with genes in all materials using PCR method.The results indicated that TEs in genes 1, 2, 3, 4, 5, 6 and 7 were stably fixed in exons among 34 ecotypes and outgroups (part of outgroups), suggesting that TEs in genes are likely going through a selective sweep.Because the divergent time of Arabidopsis thaliana from A.arenosa is 6 MYA and the divergent time of Arabidopsis thaliana from A.arenosa is 14.5-24 MYA, furthermore, TEs in genes 1, 2, 3, 5, 6 and 7 are present in all outgroups, we could infer infer that these TEs were at least inserted in genes before 14.5-24 MYA.TEs in gene 4 are absent in B. campestris L. var. italica and B. chinensis .L., but present in B. oleracea L. capitata L. and B. oleracea L. var. italica, because the divergent time of B. oleracea L. var. capiata L. from Arabidopsis thaliana is 14.5-20 MYA and the divergent times of other outgroups in Brassica were roughly estimated, then we could infer that the divergence of B. oleracea L. var. capitata L. from Arabidopsis thaliana are later than that of Brassica campestris L. and Brassica chinensis. L..Polymorphism analysis results indicated that SNP in TEs inserted in genes 1 and 6 are higher than the flanking regions, suggesting that the insertion and conservation of TEs in the coding regions of genes could improve the mutation and evolution.Natural selection test results also suggested that TE in gene1 were positively selected significantly.