Reply: Does the polyubiquitination pathway operate inside intact chloroplasts to remove proteins?

The ubiquitin-proteasome system (UPS) is the pre-eminent proteolytic system in eukaryotic cells. Its components are abundant in the cytosol and nucleus, and it selectively targets many proteins in both of these compartments for degradation. However, its functions are not restricted to nucleocytosolic proteins as it is now very well established that the UPS also targets proteins in organelles. For example, endoplasmic reticulum (ER) proteins are commonly degraded by the cytosolic proteasome following their extraction (or retrotranslocation) from the organelle, in a process termed ER-associated protein degradation (ERAD). In recent years, it has emerged that even proteins in endosymbiotic organelles (mitochondria and chloroplasts) are processed by ERAD-analogous systems. Ubiquitin-dependent degradation of chloroplast-resident proteins was initially described as a regulatory mechanism governing the chloroplast protein import machinery. This so called chloroplast-associated protein degradation (CHLORAD) system was assumed to act only at the surface of the organelle owing to the physical barrier presented by the double envelope membrane. However, recent results suggested that the UPS may have a more extensive role in regulating chloroplast proteins, affecting even those located internally. Though somewhat surprising, these results were not entirely unpredictable given that there are numerous historical reports suggesting ubiquitin action in chloroplasts, and there is increasing evidence that the UPS acts on internal mitochondrial proteins. We review the relevant literature, address corresponding criticisms, and present additional data supporting the possibility of UPS action inside chloroplasts

Coping strategies and health-related quality of life in children and adolescents with type 1 diabetes

The aim of this study was to identify relationships between coping strategies and different aspects of health-related quality of life in children with type 1 diabetes measured with the Croatian translation of the PedsQL 4.0 Generic Core Scales and PedsQL Diabetes Module. The sample consisted of 199 schoolchildren: 47 patients with type 1 diabetes and 152 healthy children. Children health problems were rated with PedsQL 4.0 Generic Core Scale and with PedsQL Diabetes Module. Coping strategies were measured with The Coping Strategies Inventory for Children and Adolescents. The results showed that all subscales of the PedsQL 4.0 Generic Core Scales and the PedsQL Diabetes Module have satisfactory reliability with the majority of scales exceeding a Cronbach α of 0,70. Significant correlations were found between coping strategies and different aspects of health-related quality of life and those correlations were higher in girls than in boys. The findings of the present study suggest that child psychologists and clinicians treating children and adolescents suffering diabetes should address coping strategies related to specific health-related problems and assist them in developing more effective ways of coping

Genome-wide meta-analysis of muscle weakness identifies 15 susceptibility loci in older men and women.

Low muscle strength is an important heritable indicator of poor health linked to morbidity and mortality in older people. In a genome-wide association study meta-analysis of 256,523 Europeans aged 60 years and over from 22 cohorts we identify 15 loci associated with muscle weakness (European Working Group on Sarcopenia in Older People definition: n = 48,596 cases, 18.9% of total), including 12 loci not implicated in previous analyses of continuous measures of grip strength. Loci include genes reportedly involved in autoimmune disease (HLA-DQA1 p = 4 × 10-17), arthritis (GDF5 p = 4 × 10-13), cell cycle control and cancer protection, regulation of transcription, and others involved in the development and maintenance of the musculoskeletal system. Using Mendelian randomization we report possible overlapping causal pathways, including diabetes susceptibility, haematological parameters, and the immune system. We conclude that muscle weakness in older adults has distinct mechanisms from continuous strength, including several pathways considered to be hallmarks of ageing

Genome-wide meta-analysis of muscle weakness identifies 15 susceptibility loci in older men and women

Low muscle strength is an important heritable indicator of poor health linked to morbidity and mortality in older people. In a genome-wide association study meta-analysis of 256,523 Europeans aged 60 years and over from 22 cohorts we identify 15 loci associated with muscle weakness (European Working Group on Sarcopenia in Older People definition: n = 48,596 cases, 18.9% of total), including 12 loci not implicated in previous analyses of continuous measures of grip strength. Loci include genes reportedly involved in autoimmune disease (HLA-DQA1p = 4 × 10−17), arthritis (GDF5p = 4 × 10−13), cell cycle control and cancer protection, regulation of transcription, and others involved in the development and maintenance of the musculoskeletal system. Using Mendelian randomization we report possible overlapping causal pathways, including diabetes susceptibility, haematological parameters, and the immune system. We conclude that muscle weakness in older adults has distinct mechanisms from continuous strength, including several pathways considered to be hallmarks of ageing

Regulation of chloroplast protein import by the ubiquitin E3 ligase SP1 is important for stress tolerance in plants

Chloroplasts are the organelles responsible for photosynthesis in plants. The chloroplast proteome comprises ∼3,000 different proteins, including components of the photosynthetic apparatus, which are highly abundant. Most chloroplast proteins are nucleus-encoded and imported following synthesis in the cytosol. Such import is mediated by multiprotein complexes in the envelope membranes that surround each organelle. The translocon at the outer envelope membrane of chloroplasts (TOC) mediates client protein recognition and early stages of import. The TOC apparatus is regulated by the ubiquitin-proteasome system (UPS) in a process controlled by the envelope-localized ubiquitin E3 ligase SUPPRESSOR OF PPI1 LOCUS1 (SP1). Previous work showed that SP1-mediated regulation of chloroplast protein import contributes to the organellar proteome changes that occur during plant development (e.g., during de-etiolation). Here, we reveal a critical role for SP1 in plant responses to abiotic stress, which is a major and increasing cause of agricultural yield losses globally. Arabidopsis plants lacking SP1 are hypersensitive to salt, osmotic, and oxidative stresses, whereas plants overexpressing SP1 are considerably more stress tolerant than wild-type. We present evidence that SP1 acts to deplete the TOC apparatus under stress conditions to limit the import of photosynthetic apparatus components, which may attenuate photosynthetic activity and reduce the potential for reactive oxygen species production and photo-oxidative damage. Our results indicate that chloroplast protein import is responsive to environmental cues, enabling dynamic regulation of the organellar proteome, and suggest new approaches for improving stress tolerance in crops

Data from: Neofunctionalization within the Omp85 protein superfamily during chloroplast evolution

The Toc75 and OEP80 proteins reside in the chloroplast outer envelope membrane. Both are members of the Omp85 superfamily of β-barrel proteins, and both are essential in Arabidopsis plants with important roles throughout development. Toc75 forms the translocation channel of the TOC complex, which is responsible for importing nucleus-encoded proteins into chloroplasts, while the function of OEP80 remains uncertain. Deficiency of Toc75 in plants that have artificially reduced OEP80 levels suggests that the latter may be involved in the biogenesis of β-barrel proteins, in similar fashion to Omp85-related proteins in other systems. To elucidate the evolutionary relationship between the two proteins, we conducted a phylogenetic analysis using 48 sequences from diverse species. This indicated that Toc75 and OEP80 belong to sister groups in the Omp85 superfamily, and originate from a gene duplication in an ancient eukaryotic organism > 1.2 billion years ago. Our analysis also supports the notion that the Toc75 family has undergone a phase of neofunctionalization to accommodate the organelle’s newly acquired need to import proteins