Dynamique des protéines dans les premiers stades de la biogenèse des chloroplastes

Chloroplast biogenesis is a highly complex process. Upon illumination undifferentiated proplastids differentiate into green chloroplasts with thylakoid membranes and a functional photosynthetic apparatus. This transition process is very rapid and, therefore, difficult to dissect. So far the molecular regulation and the protein dynamics during this transition process is not understood. The Arabidopsis albino mutant pap7-1 is used as a genetic tool to understand the early chloroplast biogenesis process. This mutant exhibits an arrested chloroplast biogenesis and down-regulated plastid transcription. The PAP7/pTAC14 protein has been identified as a subunit of the PEP complex but its function is still elusive. In order to obtain insights into the role of PAP7/pTAC14 we determined the proteome of the homozygous albino mutants and compared it to those of light-and dark-grown wild-type plants. The mass spec data were complemented by a western-immuno-blot assays. The preliminary results show that the protein accumulation follows the transcript accumulation. Rubisco does not accumulate in the pap7-1 mutant. The majority of the nuclear-encoded antenna proteins (LHCB1, LHCB3, LHCA2) were completely absent in pap7-1 mutant. While the water-splitting complex protein PSBO accumulated to normal levels indicating that import into albino plastids is functional. The genetic blocks of the pap7-1 mutant did not affect the accumulation of mitochondrial proteins. Comparable results were obtained in the proteomic results, however in most cases the changes at the protein level were much stronger than those at the transcript level.La biogenèse des chloroplastes est un processus extrêmement complexe. Lors de l’éclairage, les proplastides non différenciés se différencient en chloroplastes verts avec des membranes thylacoïdiennes et un appareil photosynthétique fonctionnel. Ce processus de transition est très rapide et difficile à expliquer. Jusqu'à présent, la régulation moléculaire et la dynamique des protéines au cours de ce processus transitoire ne sont pas claires. Le mutant albino d'Arabidopsis pap7-1 a été utilisé comme outil génétique pour comprendre le processus précoce de biogenèse des chloroplastes. Ce mutant présente une biogenèse de chloroplaste arrêtée et une transcription plastidique faiblement régulée. La protéine PAP7 / pTAC14 a été identifiée comme une sous-unité du complexe PEP mais sa fonction n’est pas encore connue. Afin de mieux comprendre le rôle de PAP7 / pTAC14, nous avons déterminé le protéome des mutants albinos homozygotes et nous l'avons comparé à ceux des plantes sauvages cultivés à la lumière et à l'obscurité. Les données de spectrométrie de masse ont été complétés et validés par des tests de western-immuno-blot. Les résultats montrent que l'accumulation de protéines suit l'accumulation de transcrits. Rubisco ne s'accumule pas dans le mutant pap7-1. La majorité des protéines d'antenne à codage nucléaire (LHCB1, LHCB3, LHCA2) étaient complètement absentes dans le mutant pap7-1. Alors que le PSBO a presnté des niveaux d'accumulation comparable au controle indiquant que l'importation dans les plastides albinos est fonctionnelle. Les blocs génétiques du mutant pap7-1 n'affectent pas l'accumulation de protéines mitochondriales. Des résultats comparables ont été obtenus dans les résultats protéomiques, mais dans la plupart des cas, les modifications au niveau des protéines étaient beaucoup plus fortes que celles au niveau de l'expression de gène

Dynamique des protéines dans les premiers stades de la biogenèse des chloroplastes

Chloroplast biogenesis is a highly complex process. Upon illumination undifferentiated proplastids differentiate into green chloroplasts with thylakoid membranes and a functional photosynthetic apparatus. This transition process is very rapid and, therefore, difficult to dissect. So far the molecular regulation and the protein dynamics during this transition process is not understood. The Arabidopsis albino mutant pap7-1 is used as a genetic tool to understand the early chloroplast biogenesis process. This mutant exhibits an arrested chloroplast biogenesis and down-regulated plastid transcription. The PAP7/pTAC14 protein has been identified as a subunit of the PEP complex but its function is still elusive. In order to obtain insights into the role of PAP7/pTAC14 we determined the proteome of the homozygous albino mutants and compared it to those of light-and dark-grown wild-type plants. The mass spec data were complemented by a western-immuno-blot assays. The preliminary results show that the protein accumulation follows the transcript accumulation. Rubisco does not accumulate in the pap7-1 mutant. The majority of the nuclear-encoded antenna proteins (LHCB1, LHCB3, LHCA2) were completely absent in pap7-1 mutant. While the water-splitting complex protein PSBO accumulated to normal levels indicating that import into albino plastids is functional. The genetic blocks of the pap7-1 mutant did not affect the accumulation of mitochondrial proteins. Comparable results were obtained in the proteomic results, however in most cases the changes at the protein level were much stronger than those at the transcript level.La biogenèse des chloroplastes est un processus extrêmement complexe. Lors de l’éclairage, les proplastides non différenciés se différencient en chloroplastes verts avec des membranes thylacoïdiennes et un appareil photosynthétique fonctionnel. Ce processus de transition est très rapide et difficile à expliquer. Jusqu'à présent, la régulation moléculaire et la dynamique des protéines au cours de ce processus transitoire ne sont pas claires. Le mutant albino d'Arabidopsis pap7-1 a été utilisé comme outil génétique pour comprendre le processus précoce de biogenèse des chloroplastes. Ce mutant présente une biogenèse de chloroplaste arrêtée et une transcription plastidique faiblement régulée. La protéine PAP7 / pTAC14 a été identifiée comme une sous-unité du complexe PEP mais sa fonction n’est pas encore connue. Afin de mieux comprendre le rôle de PAP7 / pTAC14, nous avons déterminé le protéome des mutants albinos homozygotes et nous l'avons comparé à ceux des plantes sauvages cultivés à la lumière et à l'obscurité. Les données de spectrométrie de masse ont été complétés et validés par des tests de western-immuno-blot. Les résultats montrent que l'accumulation de protéines suit l'accumulation de transcrits. Rubisco ne s'accumule pas dans le mutant pap7-1. La majorité des protéines d'antenne à codage nucléaire (LHCB1, LHCB3, LHCA2) étaient complètement absentes dans le mutant pap7-1. Alors que le PSBO a presnté des niveaux d'accumulation comparable au controle indiquant que l'importation dans les plastides albinos est fonctionnelle. Les blocs génétiques du mutant pap7-1 n'affectent pas l'accumulation de protéines mitochondriales. Des résultats comparables ont été obtenus dans les résultats protéomiques, mais dans la plupart des cas, les modifications au niveau des protéines étaient beaucoup plus fortes que celles au niveau de l'expression de gène

Protein dynamics in early steps of chloroplast biogenesis

La biogenèse des chloroplastes est un processus extrêmement complexe. Lors de l’éclairage, les proplastides non différenciés se différencient en chloroplastes verts avec des membranes thylacoïdiennes et un appareil photosynthétique fonctionnel. Ce processus de transition est très rapide et difficile à expliquer. Jusqu'à présent, la régulation moléculaire et la dynamique des protéines au cours de ce processus transitoire ne sont pas claires. Le mutant albino d'Arabidopsis pap7-1 a été utilisé comme outil génétique pour comprendre le processus précoce de biogenèse des chloroplastes. Ce mutant présente une biogenèse de chloroplaste arrêtée et une transcription plastidique faiblement régulée. La protéine PAP7 / pTAC14 a été identifiée comme une sous-unité du complexe PEP mais sa fonction n’est pas encore connue. Afin de mieux comprendre le rôle de PAP7 / pTAC14, nous avons déterminé le protéome des mutants albinos homozygotes et nous l'avons comparé à ceux des plantes sauvages cultivés à la lumière et à l'obscurité. Les données de spectrométrie de masse ont été complétés et validés par des tests de western-immuno-blot. Les résultats montrent que l'accumulation de protéines suit l'accumulation de transcrits. Rubisco ne s'accumule pas dans le mutant pap7-1. La majorité des protéines d'antenne à codage nucléaire (LHCB1, LHCB3, LHCA2) étaient complètement absentes dans le mutant pap7-1. Alors que le PSBO a presnté des niveaux d'accumulation comparable au controle indiquant que l'importation dans les plastides albinos est fonctionnelle. Les blocs génétiques du mutant pap7-1 n'affectent pas l'accumulation de protéines mitochondriales. Des résultats comparables ont été obtenus dans les résultats protéomiques, mais dans la plupart des cas, les modifications au niveau des protéines étaient beaucoup plus fortes que celles au niveau de l'expression de gène.Chloroplast biogenesis is a highly complex process. Upon illumination undifferentiated proplastids differentiate into green chloroplasts with thylakoid membranes and a functional photosynthetic apparatus. This transition process is very rapid and, therefore, difficult to dissect. So far the molecular regulation and the protein dynamics during this transition process is not understood. The Arabidopsis albino mutant pap7-1 is used as a genetic tool to understand the early chloroplast biogenesis process. This mutant exhibits an arrested chloroplast biogenesis and down-regulated plastid transcription. The PAP7/pTAC14 protein has been identified as a subunit of the PEP complex but its function is still elusive. In order to obtain insights into the role of PAP7/pTAC14 we determined the proteome of the homozygous albino mutants and compared it to those of light-and dark-grown wild-type plants. The mass spec data were complemented by a western-immuno-blot assays. The preliminary results show that the protein accumulation follows the transcript accumulation. Rubisco does not accumulate in the pap7-1 mutant. The majority of the nuclear-encoded antenna proteins (LHCB1, LHCB3, LHCA2) were completely absent in pap7-1 mutant. While the water-splitting complex protein PSBO accumulated to normal levels indicating that import into albino plastids is functional. The genetic blocks of the pap7-1 mutant did not affect the accumulation of mitochondrial proteins. Comparable results were obtained in the proteomic results, however in most cases the changes at the protein level were much stronger than those at the transcript level

Dynamique des protéines dans les premiers stades de la biogenèse des chloroplastes

Chloroplast biogenesis is a highly complex process. Upon illumination undifferentiated proplastids differentiate into green chloroplasts with thylakoid membranes and a functional photosynthetic apparatus. This transition process is very rapid and, therefore, difficult to dissect. So far the molecular regulation and the protein dynamics during this transition process is not understood. The Arabidopsis albino mutant pap7-1 is used as a genetic tool to understand the early chloroplast biogenesis process. This mutant exhibits an arrested chloroplast biogenesis and down-regulated plastid transcription. The PAP7/pTAC14 protein has been identified as a subunit of the PEP complex but its function is still elusive. In order to obtain insights into the role of PAP7/pTAC14 we determined the proteome of the homozygous albino mutants and compared it to those of light-and dark-grown wild-type plants. The mass spec data were complemented by a western-immuno-blot assays. The preliminary results show that the protein accumulation follows the transcript accumulation. Rubisco does not accumulate in the pap7-1 mutant. The majority of the nuclear-encoded antenna proteins (LHCB1, LHCB3, LHCA2) were completely absent in pap7-1 mutant. While the water-splitting complex protein PSBO accumulated to normal levels indicating that import into albino plastids is functional. The genetic blocks of the pap7-1 mutant did not affect the accumulation of mitochondrial proteins. Comparable results were obtained in the proteomic results, however in most cases the changes at the protein level were much stronger than those at the transcript level.La biogenèse des chloroplastes est un processus extrêmement complexe. Lors de l’éclairage, les proplastides non différenciés se différencient en chloroplastes verts avec des membranes thylacoïdiennes et un appareil photosynthétique fonctionnel. Ce processus de transition est très rapide et difficile à expliquer. Jusqu'à présent, la régulation moléculaire et la dynamique des protéines au cours de ce processus transitoire ne sont pas claires. Le mutant albino d'Arabidopsis pap7-1 a été utilisé comme outil génétique pour comprendre le processus précoce de biogenèse des chloroplastes. Ce mutant présente une biogenèse de chloroplaste arrêtée et une transcription plastidique faiblement régulée. La protéine PAP7 / pTAC14 a été identifiée comme une sous-unité du complexe PEP mais sa fonction n’est pas encore connue. Afin de mieux comprendre le rôle de PAP7 / pTAC14, nous avons déterminé le protéome des mutants albinos homozygotes et nous l'avons comparé à ceux des plantes sauvages cultivés à la lumière et à l'obscurité. Les données de spectrométrie de masse ont été complétés et validés par des tests de western-immuno-blot. Les résultats montrent que l'accumulation de protéines suit l'accumulation de transcrits. Rubisco ne s'accumule pas dans le mutant pap7-1. La majorité des protéines d'antenne à codage nucléaire (LHCB1, LHCB3, LHCA2) étaient complètement absentes dans le mutant pap7-1. Alors que le PSBO a presnté des niveaux d'accumulation comparable au controle indiquant que l'importation dans les plastides albinos est fonctionnelle. Les blocs génétiques du mutant pap7-1 n'affectent pas l'accumulation de protéines mitochondriales. Des résultats comparables ont été obtenus dans les résultats protéomiques, mais dans la plupart des cas, les modifications au niveau des protéines étaient beaucoup plus fortes que celles au niveau de l'expression de gène

The role of plant growth promoting rhizobacteria in plant drought stress responses.

Climate change has exacerbated the effects of abiotic stresses on plant growth and productivity. Drought is one of the most important abiotic stress factors that interfere with plant growth and development. Plant selection and breeding as well as genetic engineering methods used to improve crop drought tolerance are expensive and time consuming. Plants use a myriad of adaptative mechanisms to cope with the adverse effects of drought stress including the association with beneficial microorganisms such as plant growth promoting rhizobacteria (PGPR). Inoculation of plant roots with different PGPR species has been shown to promote drought tolerance through a variety of interconnected physiological, biochemical, molecular, nutritional, metabolic, and cellular processes, which include enhanced plant growth, root elongation, phytohormone production or inhibition, and production of volatile organic compounds. Therefore, plant colonization by PGPR is an eco-friendly agricultural method to improve plant growth and productivity. Notably, the processes regulated and enhanced by PGPR can promote plant growth as well as enhance drought tolerance. This review addresses the current knowledge on how drought stress affects plant growth and development and describes how PGPR can trigger plant drought stress responses at the physiological, morphological, and molecular levels

The Impact of Pesticide Residues on Soil Health for Sustainable Vegetable Production in Arid Areas

The assessment of pesticide residues in agricultural soils is an essential prerogative in maintaining environmental health standards. Intensive vegetable cultivation is practiced in the Al-Kharj area of the eastern Najd region of Saudi Arabia, where excessive applications of agrochemicals are reported to pollute vegetable-growing soils, challenging the sustainable management of soils and groundwater resources. This study aimed to monitor the levels of thirty-two types of pesticide residues in the soils of vegetable fields and the estimated potential health risk for humans due to non-dietary exposure to pesticides in soils in the Al-Kharj region. Pesticide residues were evaluated at 0–10 cm and 10–20 cm depths at 20 sampling sites from Al-Kharj. Gas chromatograph-mass spectrometry, coupled with a quadrupole mass spectrometer with a GC column, was used in the analysis. The results indicated that agrochemical residues show prolonged soil pollution that may cause adverse impacts on human and environment. Herbicides Atrazine, Isoproturpon, and Linuron have been detected in the soils, and these pose many problematic environmental threats. Bromoxynil, Pendimetholin, and Diclofop-methyl could be used as per the recommendations to sustainably manage soil and water resources in the Al-Kharj area. Resmethrin, Methidathion, Ethoprophos, Tetramethrin, Bromophis-methyl, Bifenthion, Permethrin, Fenoxycarb, Cyfluthrin, Phosmet, and Azinophos-methyl can be used safely in the Al-Kharj agricultural area, maintaining sustainable soils and water resources. Applications of Carbaryl require sufficient care, while Endosulfan, Deltamethrin, Lindane, Chlorpyrifos, Chlorpyrifos-methly, Dimethoate, Heptachlor, and Mevinphos, which are detected in soils, require policy guidelines to limit the use to ensure sustainability. Policy interventions need to be formulated to increase the sustainability of soil management and groundwater resources in the Al-Kharj region to ensure the safety of people who are in direct contact with the agrochemicals used and to ensure the safety of agricultural products generated in this region

PAP8/pTAC6 Is Part of a Nuclear Protein Complex and Displays RNA Recognition Motifs of Viral Origin

International audienceChloroplast biogenesis depends on a complex transcriptional program involving coordinated expression of plastid and nuclear genes. In particular, photosynthesis-associated plastid genes are expressed by the plastid-encoded polymerase (PEP) that undergoes a structural rearrangement during chloroplast formation. The prokaryotic-type core enzyme is rebuilt into a larger complex by the addition of nuclear-encoded PEP-associated proteins (PAP1 to PAP12). Among the PAPs, some have been detected in the nucleus (PAP5 and PAP8), where they could serve a nuclear function required for efficient chloroplast biogenesis. Here, we detected PAP8 in a large nuclear subcomplex that may include other subunits of the plastid-encoded RNA polymerase. We have made use of PAP8 recombinant proteins in Arabidopsis thaliana to decouple its nucleus- and chloroplast-associated functions and found hypomorphic mutants pointing at essential amino acids. While the origin of the PAP8 gene remained elusive, we have found in its sequence a micro-homologous domain located within a large structural homology with a rhinoviral RNA-dependent RNA polymerase, highlighting potential RNA recognition motifs in PAP8. PAP8 in vitro RNA binding activity suggests that this domain is functional. Hence, we propose that the acquisition of PAPs may have occurred during evolution by different routes, including lateral gene transfer

Bradyrhizobium japonicum IRAT FA3 promotes salt tolerance through jasmonic acid priming in Arabidopsis thaliana

Abstract Background Plant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants’ responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress. Results The plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress. Conclusion Our data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance

Nucleo‐plastidic PAP 8/ pTAC 6 couples chloroplast formation with photomorphogenesis

International audienceThe initial greening of angiosperms involves light activation of photoreceptors that trigger photomorphogenesis, followed by the development of chloroplasts. In these semi-autonomous organelles, construction of the photosynthetic apparatus depends on the coordination of nuclear and plastid gene expression. Here, we show that the expression of PAP8, an essential subunit of the plastid-encoded RNA polymerase (PEP) in Arabidopsis thaliana, is under the control of a regulatory element recognized by the photomorphogenic factor HY5. PAP8 protein is localized and active in both plastids and the nucleus, and particularly required for the formation of late photobodies. In the pap8 albino mutant, phytochrome-mediated signalling is altered, degradation of the chloroplast development repressors PIF1/PIF3 is disrupted, HY5 is not stabilized, and the expression of the photomorphogenesis regulator GLK1 is impaired. PAP8 translocates into plastids via its targeting pre-sequence, interacts with the PEP and eventually reaches the nucleus, where it can interact with another PEP subunit pTAC12/HMR/PAP5. Since PAP8 is required for the phytochrome B-mediated signalling cascade and the reshaping of the PEP activity, it may coordinate nuclear gene expression with PEP-driven chloroplastic gene expression during chloroplast biogenesis