Global insights into duplicated gene expression and alternative splicing in polyploid Brassica napus under heat, cold, and drought stress.

Polyploidy has been a prevalent process during plant evolution and it has made a major impact on the structure and evolution of plant genomes. Many important crop plants are polyploid. There is considerable interest in expression patterns of duplicated genes in polyploids. Alternative splicing (AS) is a fundamental aspect of gene expression that produces multiple final transcript types from a single type of mRNAs. The effects of abiotic stress conditions on AS in polyploids has received little attention. We conducted a global transcriptome analysis of Brassica napus, an allotetraploid derived from B. rapa (AT ) and B. oleracea (CT ), by RNA-Seq of plants subjected to cold, heat, and drought stress treatments. Analyses of 27,360 pairs of duplicated genes revealed overall AT subgenome biases in gene expression and CT subgenome biases in the extent of alternative splicing under all three stress treatments. More genes increased in expression than decreased in response to the stresses. Negative correlations were found between expression levels and AS frequency for each type of AS. Cold stress produced the greatest changes in gene expression and AS. Cold-induced AS changes were more likely to be shared with those generated by drought than by heat stress. We used homeologs of FLC and CCA1 as case studies to show the dynamics of how duplicates in a polyploid respond to cold stress. Our results suggest that divergence in gene expression and AS patterns between duplicated genes may increase the flexibility of polyploids when responding to abiotic stressors.