Maturase proteins in organellar group-II intron splicing in plants

Group II introns are found in bacteria, mitochondria of yeast, and in larger numbers in plant organellar genomes, where they interrupt the coding sequences of essential genes required for genome expression, photosynthesis or respiration. Several group II introns have been shown to self-splice in vitro, i.e. are ribozymes. In vivo however, these introns are dependent upon protein cofactors for efficient splicing. Such proteins are clustered into two main groups: (i) maturase proteins recruited from their host genomes; (ii) proteins encoded within the introns themselves, the so-called maturases, which are the subject of our proposal. Our own previous studies have provided genetic, and for MatK and MatR also biochemical evidences, that maturases have ‘given-up’ intron-specificity and now serve multiple introns in trans. This is important from an evolutionary point of view, as group II introns are mechanistically and structurally related to nuclear introns and the spliceosome. It is widely accepted that group II introns are the ancestors of spliceosomal introns, which invaded the nucleus in eukaryotes via the organellar endosymbiosis. Moreover, maturases are related to the core spliceosomal factor Prp8. Therefore, maturases are an exciting model for a protein factor of an early, primitive spliceosome. In sum, organellar maturases are of general importance for two reasons: 1. They are essential for the biogenesis of plant mitochondria and chloroplasts, i.e. for two of the arguably most important biological processes: photosynthesis and respiration. 2. Plant organellar maturases and group II introns are a model for the evolution of the early nuclear spliceosome. We believe that a key for understanding the biological role of maturases is to determine their mechanistic impact on splicing. We hypothesize that all maturases are associating with multiple intron RNAs in vivo – this still needs to be demonstrated for four out of six maturase. We further hypothesize that organellar maturases have gained the ability to serve multiple introns by acquiring versatility in intron recognition and intron structure modification. We propose to test these hypotheses by studying all six plant organellar maturases in hitherto unprecedented mechanistic detail. We intend (i) to reduce the expression of all six maturases via mutations and thus test their impact on organellar splicing; (ii) to establish their protein partners and RNA-ligands in vivo, using immunoenrichment and subsequent protein mass spectrometry or highthroughput RNA analysis; and (iii) to characterize the specific mechanistic role of each organellar maturase in splicing of selected group II introns by footprinting techniques and complementing genetic analyses. In the end, we expect to understand how maturases mediate multiple splicing events at molecular resolution.

Principal Investigators
Schmitz-Linneweber, Christian Prof. Dr. (Details) (Genetics)

Financer
German Israel Foundation

Duration of Project
Start date: 01/2014
End date: 12/2017

Last updated on 2020-01-06 at 17:49