Abstract
Alternative splicing, which generates multiple transcripts from the same gene and potentially different protein isoforms, is a key posttranscriptional regulatory mechanism for expanding proteomic diversity and functional complexity in higher eukaryotes. The most recent estimates, based on whole transcriptome sequencing, indicate that about 95 % of human and 60 % of Arabidopsis multi-exon genes undergo alternative splicing, suggesting important roles for this mechanism in biological processes. However, while the misregulation of alternative splicing has been associated with many human diseases, its biological relevance in plant systems is just beginning to unfold. We review here the few plant genes for which the production of multiple splice isoforms has been reported to have a clear in vivo functional impact. These case studies implicate alternative splicing in the control of a wide range of physiological and developmental processes, including photosynthetic and starch metabolism, hormone signaling, seed germination, root growth and flowering, as well as in biotic and abiotic stress responses. Future functional characterization of alternative splicing events and identification of the transcripts targeted by major regulators of this versatile means of modulating gene expression should uncover the breadth of its physiological significance in higher plants.
Highlights
The majority of eukaryotic genes have their coding exonic regions interrupted by stretches of non-coding intronic sequences
This knockout insertion mutant is unable to germinate in the absence of sucrose due to a severe block in peroxisomal β-oxidation and displays insensitivity to Indole-3-Butyric Acid (IBA), which is converted in peroxisomes into the active auxin Indole-3-Acetic Acid (IAA) (Lee et al, 2006). Full rescue of these phenotypes was only observed upon complementation with OsPEX5L, which yeast twohybrid assays showed to be the sole isoform capable of interacting with PEX7. These results suggested that the long OsPEX5 isoform is involved in both PTS1 and PTS2 import, whereas the short isoform is only related to PTS1 import
With recent global transcriptome analyses indicating that the majority of genes encoded by higher plants undergo alternative splicing, a future major challenge will be to uncover the biological significance of this key posttranscriptional regulatory mechanism in plant systems
Summary
The majority of eukaryotic genes have their coding exonic regions interrupted by stretches of non-coding intronic sequences. Dinesh-Kumar and Baker (2000) later showed that the NL splice variant arises from retention of an alternative exon within intron 3, causing a change in the ORF that includes a PTC and leads to exclusion of most of the LRR domain Expression of both NS and NL transcripts, either independently or in combination, in TMV-susceptible tobacco plants indicated that both isoforms are required to yield fully resistant plants, and that the ratio between the two is fundamental in this defense response. Instead of interacting with the full-length R protein, the truncated versions could function as adaptor proteins for downstream signaling events (Gassmann, 2008)
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