Extensive divergence in alternative splicing patterns after gene and genome duplication during the evolutionary history of Arabidopsis.

Gene duplication at various scales, from single gene duplication to whole-genome (WG) duplication, has occurred throughout eukaryotic evolution and contributed greatly to the large number of duplicated genes in the genomes of many eukaryotes. Previous studies have shown divergence in expression patterns of many duplicated genes at various evolutionary time scales and cases of gain of a new function or expression pattern by one duplicate or partitioning of functions or expression patterns between duplicates. Alternative splicing (AS) is a fundamental aspect of the expression of many genes that can increase gene product diversity and affect gene regulation. However, the evolution of AS patterns of genes duplicated by polyploidy, as well as in a sizable number of duplicated gene pairs in plants, has not been examined. Here, we have characterized conservation and divergence in AS patterns in genes duplicated by a polyploidy event during the evolutionary history of Arabidopsis thaliana. We used reverse transcription-polymerase chain reaction to assay 104 WG duplicates in six organ types and in plants grown under three abiotic stress treatments to detect organ- and stress-specific patterns of AS. Differences in splicing patterns in one or more organs, or under stress conditions, were found between the genes in a large majority of the duplicated pairs. In a few cases, AS patterns were the same between duplicates only under one or more abiotic stress treatments and not under normal growing conditions or vice versa. We also examined AS in 42 tandem duplicates and we found patterns of AS roughly comparable with the genes duplicated by polyploidy. The alternatively spliced forms in some of the genes created premature stop codons that would result in missing or partial functional domains if the transcripts are translated, which could affect gene function and cause functional divergence between duplicates. Our results indicate that AS patterns have diverged considerably after gene and genome duplication during the evolutionary history of the Arabidopsis lineage, sometimes in an organ- or stress-specific manner. AS divergence between duplicated genes may have contributed to gene functional evolution and led to preservation of some duplicated genes.