Bacterial group II introns encode maturase proteins required for splicing. In organelles of photosynthetic land plants, most of the group II introns have lost the reading frames for maturases. Here, we show that the plastidial maturase MatK not only interacts with its encoding intron within trnK -UUU, but also with six additional group II introns, all belonging to intron subclass IIA. Mapping analyses of RNA binding sites revealed MatK to recognize multiple regions within the trnK intron. Organellar group II introns are considered to be the ancestors of nuclear spliceosomal introns. That MatK associates with multiple intron ligands makes it an attractive model for an early trans -acting nuclear splicing activity.

Genes for pentatricopeptide repeat (PPR) proteins are found in all eukaryotic genomes analyzed but are particularly abundant in land plants. The majority of analyzed PPR proteins play a role in the processing or translation of organellar RNAs. Few PPR proteins have been studied in detail, and the functional repertoire and mechanisms of action of proteins in the PPR family are poorly understood. Here we analyzed a maize ortholog of the embryo-essential Arabidopsis thaliana gene AtPPR5. A genome-wide analysis of chloroplast RNAs that coimmunoprecipitate with Zea mays PPR5 (ZmPPR5) demonstrated that ZmPPR5 is bound in vivo to the unspliced precursor of trnG-UCC. Null and hypomorphic Zmppr5 insertion mutants are embryo viable but are deficient for chloroplast ribosomes and die as seedlings. These mutants show a dramatic decrease in both spliced and unspliced trnG-UCC RNAs, while the transcription of trnG-UCC is unaffected. These results, together with biochemical data documenting the sequence-specific binding of recombinant PPR5 to the trnG-UCC group II intron, suggest that PPR5 stabilizes the trnG-UCC precursor by directly binding and protecting an endonuclease-sensitive site. These findings add to the evidence that chloroplast-localized PPR proteins that are embryo essential in Arabidopsis typically function in the biogenesis of the plastid translation machinery.

Numerous studies highlighted the beneficial effects of the Mediterranean diet (MD) in maintaining health, especially during ageing. Even neurodegeneration, which is part of the natural ageing process, as well as the foundation of ageing-related neurodegenerative disorders like Alzheimer’s and Parkinson’s disease (PD), was successfully targeted by MD. In this regard, olive oil and its polyphenolic constituents have received increasing attention in the last years. Thus, this study focuses on two main olive oil polyphenols, hydroxytyrosol (HT) and oleuropein aglycone (OLE), and their effects on ageing symptoms with special attention to PD. In order to avoid long-lasting, expensive, and ethically controversial experiments, the established invertebrate model organism Caenorhabditis elegans was used to test HT and OLE treatments. Interestingly, both polyphenols were able to increase the survival after heat stress, but only HT could prolong the lifespan in unstressed conditions. Furthermore, in aged worms, HT and OLE caused improvements of locomotive behavior and the attenuation of autofluorescence as a marker for ageing. In addition, by using three different C. elegans PD models, HT and OLE were shown i) to enhance locomotion in worms suffering from α-synuclein-expression in muscles or rotenone exposure, ii) to reduce α-synuclein accumulation in muscles cells, and iii) to prevent neurodegeneration in α-synuclein-containing dopaminergic neurons. Hormesis, antioxidative capacities and an activity-boost of the proteasome & phase II detoxifying enzymes are discussed as potential underlying causes for these beneficial effects. Further biological and medical trials are indicated to assess the full potential of HT and OLE and to uncover their mode of action.

Chloroplast RNA metabolism is mediated by a multitude of nuclear encoded factors, many of which are highly specific for individual RNA processing events. In addition, a family of chloroplast ribonucleoproteins (cpRNPs) has been suspected to regulate larger sets of chloroplast transcripts. This together with their propensity for posttranslational modifications in response to external cues suggested a potential role of cpRNPs in the signal-dependent coregulation of chloroplast genes. We show here on a transcriptome-wide scale that the Arabidopsis thaliana cpRNPs CP31A and CP29A (for 31 kD and 29 kD chloroplast protein, respectively), associate with large, overlapping sets of chloroplast transcripts. We demonstrate that both proteins are essential for resistance of chloroplast development to cold stress. They are required to guarantee transcript stability of numerous mRNAs at low temperatures and under these conditions also support specific processing steps. Fine mapping of cpRNP–RNA interactions in vivo suggests multiple points of contact between these proteins and their RNA ligands. For CP31A, we demonstrate an essential function in stabilizing sense and antisense transcripts that span the border of the small single copy region and the inverted repeat of the chloroplast genome. CP31A associates with the common 3′-terminus of these RNAs and protects them against 3′-exonucleolytic activity.

Chloroplast RNA metabolism is controlled and excecuted by hundreds of nuclear-encoded, chloroplast-localized RNA binding proteins. Contrary to the nucleo-cytosolic compartment or bacteria, there is little evidence for non-coding RNAs that play a role as riboregulators of chloroplasts. We mined deep-sequencing datasets to identify short (16-28 nt) RNAs in the chloroplast genome and found 50 abundant small RNAs (sRNAs) represented by multiple, in some cases, thousands of sequencing reads, whereas reads are in general absent from the surrounding sequence space. Other than sRNAs representing the most highly abundant mRNAs, tRNAs and rRNAs, most sRNAs are located in non-coding regions and many are found a short distance upstream of start codons. By transcript end mapping we show that the 5' and 3' termini of chloroplast RNAs coincide with the ends of sRNAs. Sequences of sRNAs identified in Arabidopsis are conserved between different angiosperm species and in several cases, we identified putative orthologs in rice deep sequencing datasets. Recently, it was suggested that small chloroplast RNA fragments could result from the protective action of pentatricopeptide repeat (PPR) proteins against exonucleases, i.e. footprints of RNA binding proteins. Our data support this scenario on a transcriptome-wide level and suggest that a large number of sRNAs are in fact remnants of PPR protein targets.

Parkinson’s disease (PD) is the second most prevalent late-age onset neurodegenerative disorder, affecting 1% of the population after the age of about 60 years old and 4% of those over 80 years old, causing motor impairments and cognitive dysfunction. Increasing evidence indicates that Mediterranean diet (MD) exerts beneficial effects in maintaining health, especially during ageing and by the prevention of neurodegenerative disorders. In this regard, olive oil and its biophenolic constituents like hydroxytyrosol (HT) have received growing attention in the past years. Thus, in the current study we test the health-promoting effects of two hydroxytyrosol preparations, pure HT and Hidrox^® (HD), which is hydroxytyrosol in its “natural” environment, in the established invertebrate model organism Caenorhabditis elegans. HD exposure led to much stronger beneficial locomotion effects in wild type worms compared to HT in the same concentration. Consistent to this finding, in OW13 worms, a PD-model characterized by α-synuclein expression in muscles, HD exhibited a significant higher effect on α-synuclein accumulation and swim performance than HT, an effect partly confirmed also in swim assays with the UA44 strain, which features α-synuclein expression in DA-neurons. Interestingly, beneficial effects of HD and HT treatment with similar strength were detected in the lifespan and autofluorescence of wild-type nematodes, in the neuronal health of UA44 worms as well as in the locomotion of rotenone-induced PD-model. Thus, the hypothesis that HD features higher healthspan-promoting abilities than HT was at least partly confirmed. Our study demonstrates that HD polyphenolic extract treatment has the potential to partly prevent or even treat ageing-related neurodegenerative diseases and ageing itself. Future investigations including mammalian models and human clinical trials are needed to uncover the full potential of these olive compounds.