RESUMEN
Twin-arginine translocation (Tat) pathways have been well-characterized in bacteria and chloroplasts. Genes encoding a TatC protein are found in almost all plant mitochondrial genomes but to date these have not been extensively investigated. For the first time it could be demonstrated that this mitochondrial-encoded TatC is a functional gene that is translated into a protein in the model plant Arabidopsis thaliana A TatB--like subunit localized to the inner membrane was also identified that is nuclear-encoded and is essential for plant growth and development, indicating that plants potentially require a Tat pathway for mitochondrial biogenesis.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Mitocondrias/metabolismo , Peptidil Transferasas/metabolismo , Subunidades de Proteína/metabolismo , Secuencia de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Proteínas de Escherichia coli/química , Genes Esenciales , Genes de Plantas , Genoma Mitocondrial , Proteínas Fluorescentes Verdes/metabolismo , Concentración de Iones de Hidrógeno , Membranas Mitocondriales/metabolismo , Proteínas Mitocondriales/química , Proteínas Mitocondriales/genética , Proteínas Mitocondriales/metabolismo , Peso Molecular , Peptidil Transferasas/química , Peptidil Transferasas/genética , Filogenia , Subunidades de Proteína/química , Subunidades de Proteína/genética , Alineación de SecuenciaRESUMEN
KEY MESSAGE: SLO4 is a mitochondrial PPR protein that is involved in editing nad4, possibly required for the efficient splicing of nad2 intron1. Pentatricopeptide repeat (PPR) proteins constitute a large protein family in flowering plants and are thought to be mostly involved in organellar RNA metabolism. The subgroup of PLS-type PPR proteins were found to be the main specificity factors of cytidine to uridine RNA editing. Identifying the targets of PLS-type PPR proteins can help in elucidating the molecular function of proteins encoded in the organellar genomes. In this study, plants lacking the SLOW GROWTH 4 PPR protein were characterized. Slo4 mutants were characterized as having restricted root growth, being late flowering and displaying an overall delayed growth phenotype. Protein levels and activity of mitochondrial complex I were decreased and putative complex I assembly intermediates accumulated in the mutant plants. An editing defect, leading to an amino acid change, in the mitochondrial nad4 transcript, encoding for a complex I subunit, was identified. Furthermore, the splicing efficiency of the first intron of nad2, encoding for another complex I subunit, was also decreased. The change in splicing efficiency could however not be linked to any editing defects in the nad2 transcript.
Asunto(s)
Proteínas de Arabidopsis/genética , Complejo I de Transporte de Electrón/genética , Proteínas Mitocondriales/genética , NADH Deshidrogenasa/genética , Secuencia de Aminoácidos , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Secuencia de Bases , Complejo I de Transporte de Electrón/metabolismo , Immunoblotting , Proteínas Mitocondriales/metabolismo , Mutación , NADH Deshidrogenasa/metabolismo , Fenotipo , Plantas Modificadas Genéticamente , Edición de ARN , Empalme del ARN , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido NucleicoRESUMEN
Sunlight represents the energy source for photosynthesis and plant growth. When growing in the field, plant photosynthesis has to manage strong fluctuations in light intensities. Regulation based on the thioredoxin (Trx) system is believed to ensure light-responsive control of photosynthetic reactions in the chloroplast. However, direct evidence for a role of this system in regulating dynamic acclimation of photosynthesis in fluctuating conditions is largely lacking. In this report we show that the ferredoxin-dependent Trxs m1 and m2 as well as the NADPH-dependent NTRC are both indispensable for photosynthetic acclimation in fluctuating light intensities. Arabidopsis mutants with combined deficiency in Trxs m1 and m2 show wild-type growth and photosynthesis under constant light condition, while photosynthetic parameters are strongly modified in rapidly alternating high and low light. Two independent trxm1m2 mutants show lower photosynthetic efficiency in high light, but surprisingly significantly higher photosynthetic efficiency in low light. Our data suggest that a main target of Trx m1 and m2 is the NADP-malate dehydrogenase involved in export of excess reductive power from the chloroplast. The decreased photosynthetic efficiency in the high-light peaks may thus be explained by a reduced capacity of the trxm1m2 mutants in the rapid light activation of this enzyme. In the ntrc mutant, dynamic responses of non-photochemical quenching of excitation energy and plastoquinone reduction state both were strongly attenuated in fluctuating light intensities, leading to a massive decrease in PSII quantum efficiency and a specific decrease in plant growth under these conditions. This is likely due to the decreased ability of the ntrc mutant to control the stromal NADP(H) redox poise. Taken together, our results indicate that NTRC is indispensable in ensuring the full range of dynamic responses of photosynthesis to optimize photosynthesis and maintain growth in fluctuating light, while Trxs m1 and m2 are indispensable for full activation of photosynthesis in the high-light periods but negatively affect photosynthetic efficiency in the low-light periods of fluctuating light.