| Summary: | <p>Abstract</p> <p>Background</p> <p>The proteasome subunit RPT5, which is essential for gametophyte development, is encoded by two genes in <it>Arabidopsis thaliana</it>; <it>RPT5a </it>and <it>RPT5b</it>. We showed previously that <it>RPT5a </it>and <it>RPT5b </it>are fully redundant in the Columbia (Col-0) accession, whereas in the Wassilewskia accession (Ws-4), <it>RPT5b </it>does not complement the effect of a strong <it>rpt5a </it>mutation in the male gametophyte, and only partially complements <it>rpt5a </it>mutation in the sporophyte. <it>RPT5b<sup>Col-0 </sup></it>and <it>RPT5b<sup>Ws-4 </sup></it>differ by only two SNPs, one located in the promoter and the other in the seventh intron of the gene.</p> <p>Results</p> <p>By exploiting natural variation at <it>RPT5b </it>we determined that the SNP located in <it>RPT5b </it>intron seven, rather than the promoter SNP, is the sole basis of this lack of redundancy. In Ws-4 this SNP is predicted to create a new splicing branchpoint sequence that induces a partial mis-splicing of the pre-mRNA, leading to the introduction of a Premature Termination Codon. We characterized 5 accessions carrying this A-to-T substitution in intron seven and observed a complete correlation between this SNP and both a 10 to 20% level of the <it>RPT5b </it>pre-mRNA mis-splicing and the lack of ability to complement an <it>rpt5a </it>mutant phenotype.</p> <p>Conclusion</p> <p>The accession-dependent unequal redundancy between <it>RPT5a </it>and <it>RPT5b </it>genes illustrates an example of evolutionary drifting between duplicated genes through alternative splicing.</p>
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