Abstract
In eukaryotes, alternative splicing of pre-mRNAs contributes significantly to the proper expression of the genome. However, the functions of many auxiliary spliceosomal proteins are still unknown. Here, we functionally characterized plant homologues of nematode suppressors of mec-8 and unc-52 (smu). We compared transcript profiles of maize (Zea mays) smu2 endosperm with those of wild-type plants and identified pre-mRNA splicing events that depend on the maize SMU2 protein. Consistent with a conserved role of plant SMU-2 homologues, Arabidopsis (Arabidopsis thaliana) smu2 mutants also show altered splicing of similar target pre-mRNAs. The Atsmu2 mutants occasionally show developmental phenotypes, including abnormal cotyledon numbers and higher seed weights. We identified AtSMU1 as one of the SMU2-interacting proteins, and Atsmu1 mutations cause similar developmental phenotypes with higher penetrance than Atsmu2. The AtSMU2 and AtSMU1 proteins are localized to the nucleus and highly prevalent in actively dividing tissues. Taken together, our data indicated that the plant SMU-1 and SMU-2 homologues appear to be involved in splicing of specific pre-mRNAs that affect multiple aspects of development.
Highlights
In eukaryotes, alternative splicing of pre-mRNAs contributes significantly to the proper expression of the genome
We identified an interaction of AtSMU2 with AtSMU1, the homologue of the nematode SMU-1 protein that was previously shown to interact with SMU-2 (Spartz et al, 2004)
We previously reported that an AtSMU2 protein with a glutathione-Stransferase (GST) tag showed strong cross-reaction with an antiserum prepared against ZmSMU2 (Chung et al, 2007)
Summary
Alternative splicing of pre-mRNAs contributes significantly to the proper expression of the genome. Consistent with a conserved role of plant SMU-2 homologues, Arabidopsis (Arabidopsis thaliana) smu mutants show altered splicing of similar target pre-mRNAs. The Atsmu mutants occasionally show developmental phenotypes, including abnormal cotyledon numbers and higher seed weights. A fraction of these proteins constitute the catalytic core components for pre-mRNA splicing, while the others are believed to be auxiliary factors. Some of these auxiliary proteins appear to be sequence-specific splicing factors (i.e. recruited to certain sets of pre-mRNAs) or their associated proteins and provide communication links between splicing and other processes in pre-mRNA and mRNA metabolism, such as transcription, capping, and 3# end formation (Jurica and Moore, 2003). SMU1 and SMU2 in Pre-mRNA Splicing and Simpson, 1998) and components of animal spliceosomes are conserved in plant genomes (Reddy, 2001). SR proteins and some spliceosomal proteins in plants appear to form a functional complex through their physical interactions (Reddy, 2004)
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