VISITING SPEAKER: Maturase proteins in higher-plants mitochondria group-II introns splicing

The expression of the mtDNA in plants is complex, particularly at the post-transcriptional level; RNA processing events which contribute to organellar genome expression include hundreds of RNA-editing events and the splicing of numerous group-II-type introns which lie within many protein-coding genes required in both respiration and organellar genome expression mediated functions. The splicing of the mt group-II introns is therefore essential for organellar function and is dependent upon different proteincous cofactors. While in non-plant systems, the splicing of group-II introns is mediated by proteins encoded within the introns themselves which are known as Maturases, only a single Maturase ORF (matR, encoded within the forth intron in nad1 gene) was retained in the mtDNA in plants; yet, its putative role(s) in the splicing of nad1 or additional organellar introns are yet to be established. Clues to other proteins are scarce, but these are likely to be encoded within the nucleus as beside MatR there are no obvious candidates among the remaining ORFs within the mtDNA. Intriguingly, in addition to matR, higher plants nuclear genomes also harbor four Maturase-related genes (nMat 1 to 4), which exist in the nucleus as self-standing ORFs out of the context of their “evolutionary related group-II introns hosts". These are all predicted to reside within the mitochondria and are therefore expected to function in the splicing of organellar introns. GFP-localization analyses indicated that the four nuc-Mats are localized to mitochondria in Arabidopsis. Analyses of the phenotypes associated with various Arabidopsis 'knock-out' mutants established the roles of the four nMats in the splicing of a different subset of mitochondrial introns.