Cis- and trans-splicing of group II introns in plant mitochondria

Mitochondrion ◽  
2008 ◽  
Vol 8 (1) ◽  
pp. 26-34 ◽  
Author(s):  
Linda Bonen
Keyword(s):  
Plant Mitochondria ◽  
Group Ii Introns ◽  
Trans Splicing ◽  
Group Ii ◽  
Cis And Trans

scholarly journals Nuclear Encoded RNA Splicing Factors in Plant Mitochondria

2009 ◽  
Author(s):  
Oren Ostersetzer-Biran ◽  
Alice Barkan
Keyword(s):  
Rna Splicing ◽  
Plant Mitochondria ◽  
Group Ii Intron ◽  
Nuclear Genes ◽  
Metabolic Energy ◽  
Splicing Factors ◽  
Group Ii Introns ◽  
Intron Splicing ◽  
Group Ii ◽  
Mitochondrial Introns

Mitochondria are the site of respiration and numerous other metabolic processes required for plant growth and development. Increased demands for metabolic energy are observed during different stages in the plants life cycle, but are particularly ample during germination and reproductive organ development. These activities are dependent upon the tight regulation of the expression and accumulation of various organellar proteins. Plant mitochondria contain their own genomes (mtDNA), which encode for a small number of genes required in organellar genome expression and respiration. Yet, the vast majority of the organellar proteins are encoded by nuclear genes, thus necessitating complex mechanisms to coordinate the expression and accumulation of proteins encoded by the two remote genomes. Many organellar genes are interrupted by intervening sequences (introns), which are removed from the primary presequences via splicing. According to conserved features of their sequences these introns are all classified as “group-II”. Their splicing is necessary for organellar activity and is dependent upon nuclear-encoded RNA-binding cofactors. However, to-date, only a tiny fraction of the proteins expected to be involved in these activities have been identified. Accordingly, this project aimed to identify nuclear-encoded proteins required for mitochondrial RNA splicing in plants, and to analyze their specific roles in the splicing of group-II intron RNAs. In non-plant systems, group-II intron splicing is mediated by proteins encoded within the introns themselves, known as maturases, which act specifically in the splicing of the introns in which they are encoded. Only one mitochondrial intron in plants has retained its maturaseORF (matR), but its roles in organellar intron splicing are unknown. Clues to other proteins required for organellar intron splicing are scarce, but these are likely encoded in the nucleus as there are no other obvious candidates among the remaining ORFs within the mtDNA. Through genetic screens in maize, the Barkan lab identified numerous nuclear genes that are required for the splicing of many of the introns within the plastid genome. Several of these genes are related to one another (i.e. crs1, caf1, caf2, and cfm2) in that they share a previously uncharacterized domain of archaeal origin, the CRM domain. The Arabidopsis genome contains 16 CRM-related genes, which contain between one and four repeats of the domain. Several of these are predicted to the mitochondria and are thus postulated to act in the splicing of group-II introns in the organelle(s) to which they are localized. In addition, plant genomes also harbor several genes that are closely related to group-II intron-encoded maturases (nMats), which exist in the nucleus as 'self-standing' ORFs, out of the context of their cognate "host" group-II introns and are predicted to reside within the mitochondria. The similarity with known group-II intron splicing factors identified in other systems and their predicted localization to mitochondria in plants suggest that nuclear-encoded CRM and nMat related proteins may function in the splicing of mitochondrial-encoded introns. In this proposal we proposed to (i) establish the intracellular locations of several CRM and nMat proteins; (ii) to test whether mutations in their genes impairs the splicing of mitochondrial introns; and to (iii) determine whether these proteins are bound to the mitochondrial introns in vivo.  

scholarly journals Group II Introns Generate Functional Chimeric Relaxase Enzymes with Modified Specificities through Exon Shuffling at Both the RNA and DNA Level

2020 ◽  
Author(s):  
Félix LaRoche-Johnston ◽  
Rafia Bosan ◽  
Benoit Cousineau
Keyword(s):  
Genetic Diversity ◽  
Insertion Site ◽  
Long Terminal Repeat Retrotransposons ◽  
Group Ii Introns ◽  
Gain Of Function ◽  
Intron Insertion ◽  
Spliceosomal Introns ◽  
Biologically Relevant ◽  
Trans Splicing ◽  
Group Ii

Abstract Group II introns are large self-splicing RNA enzymes with a broad but somewhat irregular phylogenetic distribution. These ancient retromobile elements are the proposed ancestors of approximately half the human genome, including the abundant spliceosomal introns and non-long terminal repeat retrotransposons. In contrast to their eukaryotic derivatives, bacterial group II introns have largely been considered as harmful selfish mobile retroelements that parasitize the genome of their host. As a challenge to this view, we recently uncovered a new intergenic trans-splicing pathway that generates an assortment of mRNA chimeras. The ability of group II introns to combine disparate mRNA fragments was proposed to increase the genetic diversity of the bacterial host by shuffling coding sequences. Here, we show that the Ll.LtrB and Ef.PcfG group II introns from Lactococcus lactis and Enterococcus faecalis respectively can both use the intergenic trans-splicing pathway to catalyze the formation of chimeric relaxase mRNAs and functional proteins. We demonstrated that some of these compound relaxase enzymes yield gain-of-function phenotypes, being significantly more efficient than their precursor wild-type enzymes at supporting bacterial conjugation. We also found that relaxase enzymes with shuffled functional domains are produced in biologically relevant settings under natural expression levels. Finally, we uncovered examples of lactococcal chimeric relaxase genes with junctions exactly at the intron insertion site. Overall, our work demonstrates that the genetic diversity generated by group II introns, at the RNA level by intergenic trans-splicing and at the DNA level by recombination, can yield new functional enzymes with shuffled exons, which can lead to gain-of-function phenotypes.

scholarly journals The Chloroplast Trans-Splicing RNA–Protein Supercomplex from the Green Alga Chlamydomonas reinhardtii

Cells ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 290
Author(s):  
Ulrich Kück ◽  
Olga Schmitt
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Green Alga ◽  
Evolutionary Relationship ◽  
Group Ii Introns ◽  
Discontinuous Group ◽  
Diverse Range ◽  
Ribonucleoprotein Complexes ◽  
Trans Splicing ◽  
In Trans ◽  
Group Ii

In eukaryotes, RNA trans-splicing is a significant RNA modification process for the end-to-end ligation of exons from separately transcribed primary transcripts to generate mature mRNA. So far, three different categories of RNA trans-splicing have been found in organisms within a diverse range. Here, we review trans-splicing of discontinuous group II introns, which occurs in chloroplasts and mitochondria of lower eukaryotes and plants. We discuss the origin of intronic sequences and the evolutionary relationship between chloroplast ribonucleoprotein complexes and the nuclear spliceosome. Finally, we focus on the ribonucleoprotein supercomplex involved in trans-splicing of chloroplast group II introns from the green alga Chlamydomonas reinhardtii. This complex has been well characterized genetically and biochemically, resulting in a detailed picture of the chloroplast ribonucleoprotein supercomplex. This information contributes substantially to our understanding of the function of RNA-processing machineries and might provide a blueprint for other splicing complexes involved in trans- as well as cis-splicing of organellar intron RNAs.

scholarly journals Bacterial group II introns generate genetic diversity by circularization and trans-splicing from a population of intron-invaded mRNAs

PLoS Genetics ◽  
2018 ◽  
Vol 14 (11) ◽  
pp. e1007792 ◽  
Author(s):  
Félix LaRoche-Johnston ◽  
Caroline Monat ◽  
Samy Coulombe ◽  
Benoit Cousineau
Keyword(s):  
Genetic Diversity ◽  
Group Ii Introns ◽  
Bacterial Group ◽  
Trans Splicing ◽  
Group Ii

scholarly journals Organellar Introns in Fungi, Algae, and Plants

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 2001
Author(s):  
Jigeesha Mukhopadhyay ◽  
Georg Hausner
Keyword(s):  
Gene Expression ◽  
Ribosomal Proteins ◽  
Heterologous Gene Expression ◽  
Group I Introns ◽  
Group Ii Introns ◽  
Homing Endonucleases ◽  
Organellar Genomes ◽  
Chloroplast Genomes ◽  
Group I ◽  
Group Ii

Introns are ubiquitous in eukaryotic genomes and have long been considered as ‘junk RNA’ but the huge energy expenditure in their transcription, removal, and degradation indicate that they may have functional significance and can offer evolutionary advantages. In fungi, plants and algae introns make a significant contribution to the size of the organellar genomes. Organellar introns are classified as catalytic self-splicing introns that can be categorized as either Group I or Group II introns. There are some biases, with Group I introns being more frequently encountered in fungal mitochondrial genomes, whereas among plants Group II introns dominate within the mitochondrial and chloroplast genomes. Organellar introns can encode a variety of proteins, such as maturases, homing endonucleases, reverse transcriptases, and, in some cases, ribosomal proteins, along with other novel open reading frames. Although organellar introns are viewed to be ribozymes, they do interact with various intron- or nuclear genome-encoded protein factors that assist in the intron RNA to fold into competent splicing structures, or facilitate the turn-over of intron RNAs to prevent reverse splicing. Organellar introns are also known to be involved in non-canonical splicing, such as backsplicing and trans-splicing which can result in novel splicing products or, in some instances, compensate for the fragmentation of genes by recombination events. In organellar genomes, Group I and II introns may exist in nested intronic arrangements, such as introns within introns, referred to as twintrons, where splicing of the external intron may be dependent on splicing of the internal intron. These nested or complex introns, with two or three-component intron modules, are being explored as platforms for alternative splicing and their possible function as molecular switches for modulating gene expression which could be potentially applied towards heterologous gene expression. This review explores recent findings on organellar Group I and II introns, focusing on splicing and mobility mechanisms aided by associated intron/nuclear encoded proteins and their potential roles in organellar gene expression and cross talk between nuclear and organellar genomes. Potential application for these types of elements in biotechnology are also discussed.

Self‐Splicing Group II Introns

Ribozymes ◽  
2021 ◽  
pp. 143-167
Author(s):  
Isabel Chillón ◽  
Marco Marcia
Keyword(s):  
Group Ii Introns ◽  
Group Ii ◽  
Self Splicing

scholarly journals Generalized bacterial genome editing using mobile group II introns and Cre‐ lox

2013 ◽  
Vol 9 (1) ◽  
pp. 685 ◽  
Author(s):  
Peter J Enyeart ◽  
Steven M Chirieleison ◽  
Mai N Dao ◽  
Jiri Perutka ◽  
Erik M Quandt ◽  
...  
Keyword(s):  
Genome Editing ◽  
Bacterial Genome ◽  
Group Ii Introns ◽  
Group Ii
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