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UBC Theses and Dissertations

Divergence in alternative splicing patterns between duplicated gene pairs in polyploid Brassica napus Moshgabadi, Noushin


Polyploidy is the process of genome doubling that gives rise to organisms with multiple sets of chromosomes. Expression patterns and levels of genes duplicated by polyploidy, termed homeologs, can change and gene silencing can occur after polyploidy. Alternative splicing (AS) creates multiple mature mRNAs from a single type of precursor mRNA. AS can change the level of gene expression by degradation of transcripts with premature stop codons, as well as create new protein isoforms. Little is known about how AS changes after a polyploidization event, either within a few generations after polyploidy or over evolutionary time, and what effects AS changes have on gene expression in polyploids. In this project, the evolution of alternative splicing patterns after genome duplication in allotetraploid Brassica napus and a synthetic allotetraploid B. napus was examined by RT-PCR assays of a set of 31 duplicated genes. Since genes can show different patterns of AS in different organ types and under different abiotic stresses, two different organ types (leaf and cotyledon), and two different abiotic stresses (heat and cold) were used. Comparing the AS patterns between the two homeologs in B. napus revealed that 18% of the gene pairs show AS in only one homeolog. In contrast 33% of the gene pairs in the synthetic allotetraploid showed AS in only one homeolog. Gene silencing was observed for 6% and 9% of genes in B. napus and synthetic B. napus, respectively. These results indicate that there are many changes in AS in both the synthetic B. napus and natural B. napus after polyploidy, but more AS changes occurred in the synthetic polyploid. The PASTICCINO gene showed partitioning of two AS events between the homeologs in the synthetic allopolyploid, suggesting subfunctionalization of AS forms. Results from this project indicate that AS patterns can change rapidly after polyploidy and suggest that changes in AS patterns are a major phenomenon in allopolyploids.

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