Genome-wide detection of context-sensitive alternative splicing in Arabidopsis roots

To analyze context-sensitive changes in pre-mRNA splicing pattern and gene expression, we mapped the transcriptome of iron-deficient and iron-sufficient Arabidopsis roots using the RNA-seq technology. RNA-seq data were analyzed with a newly developed software package, RACKJ (Read Analysis & Comparison Kit in Java). Subsets of 460 and 1480 genes were found to be either differentially expressed or affected in their splicing patterns upon iron deficiency. The two groups showed a small, random overlap, indicating that alternative splicing and differential gene expression represent parallel, but potentially interacting regulatory mechanisms. The majority (~95%) of the context-sensitive alternative splicing events was due to differentially retained introns. Intron retention was mostly repressed in iron-deficient plants, while exon skipping did not show a clear trend in either direction. A comparison with a similar data set for phosphate-deficient plants supported stress-repressed intron retention and revealed nutrient-specific changes of splicing patterns. It is concluded that iron and phosphate deficiency increases splicing fidelity for a subset of transcripts, probably as a means of acclimation to nutrient shortage.