Expression du génome plastidial d'Arabidopsis thaliana pendant la formation des graines

Transcription of the plastid genome, one of the three genomes (nuclear, mitochondrial and plastidial) that co-exist in the plant cell, is performed by three ARN polymerases. Two NEPs (Nucleus-Encoded Plastid RNA polymerases) transcribe mainly housekeeping genes and one PEP (plastid-encoded RNA polymerase) transcribes principally photosynthesis related genes. PEP needs transcription factors of the sigma type that are nucleus-encoded. We have previously shown that all three RNA polymerases are present in dry seeds and are necessary for efficient germination. These findings raised the question of how theses RNA polymerases come into the dry seeds and what is the importance of plastid gene expression during seed formation. To answer this question my work consisted in the characterization of plastid gene expression profiles and the expression of the components of the plastid transcriptional machinery during the three phases of seed formation, i. e. embryogenesis, maturation (embryonic photosynthesis) and desiccation. The analysis of global plastid transcriptome patterns shows that mRNAs encoding proteins engaged in photosynthesis show the highest quantitative changes during seed formation. Highest mRNA levels are observed during maturation. During desiccation, photosynthesis related mRNA levels as well as the levels of the corresponding proteins strongly decrease. Concerning the expression of NEP and PEP components, we observe also a peak of protein accumulation during maturation that is followed by a strong diminution of the protein levels. On the other hand, the corresponding mRNAs increase continuously during desiccation. This means that these mRNAs accumulate without being translated. We conclude that the storage of mRNAs coding components of the plastid transcriptional machinery in dry seeds is important for efficient germination. Regarding the limited amount of biological material that is available for these types of studies, we have developed a new method for cDNA analyses on microchips that utilises quartz plates and TIRF microscopy. In this way we can visualise single molecules and the amount of necessary material is considerable diminished. Finally, we have also partially characterized the conditions under which embryonic photosynthesis is performed. These studies show that photosynthesis occurs in a special environment that is characterized by hypoxic atmosphere and green enriched light. However, the structure and functioning of the photosynthetic apparatus in seed chloroplasts seems to be very similar to that of chloroplasts in green leaves. This opens the question of how seed photosynthesis can be efficient. On the other hand we have shown that embryonic photosynthesis is indeed very important for efficient germination. Altogether, results provide new information on the functioning of plastid photosynthesis and transcription during seed formation. They underline the importance of the accumulation of NEP and PEP coding mRNAs in dry seeds. We suggest that embryonic photosynthesis influences seed germination not only by providing reserve compounds but also by producing NEP and PEP proteins. Although the majority of these proteins are degraded during desiccation, traces persist and are stored in dry seeds thus assuring immediate transcription of the plastid genome during imbibition/stratification. Our results explain how efficiency of germination is conditioned during seed formation.L'expression du génome plastidial, un des trois génomes (nucléaire, mitochondrial et plastidial) qui coexistent dans les cellules végétales, est assurée par trois ARN polymérases. Deux NEP (Nuclear-Encoded RNA Polymerase) transcrivent la plupart des gènes de ménage tandis que la PEP (Plastid-Encoded RNA Polymerase) transcrit principalement les gènes liés à la fonction photosynthétique en s'associant à des facteurs de transcription d'origine nucléaire (facteurs sigma) importés dans le plaste. De précédents travaux dans l'équipe ont montré que, contrairement aux observations généralement admises, les trois ARN polymérases sont nécessaires pour assurer une germination efficace des graines d'Arabidopsis. L'objectif de notre travail est de comprendre comment ces enzymes ont été mises en place au cours de la formation de la graine. Pour cela, nous avons analysé l'expression de l'appareil transcriptionnel et du transcriptome plastidial durant les trois phases de formation de la graine d'Arabidopsis thaliana, c'est à dire l'embryogenèse, la maturation (phase photosynthétique) et la dessiccation. L'expression globale du transcriptome plastidial montre que les changements quantitatifs des transcrits sont les plus élevés pour les transcrits des gènes liés à la fonction photosynthétique. Ils sont très fortement exprimés pendant la phase de la maturation et diminuent ensuite, comme leurs protéines correspondantes. Nous observons également une forte accumulation des protéines codant les NEP et les sous unités de la PEP pendant la période de maturation des graines, suivie d'une forte diminution pendant la dessiccation. Cependant, les ARNm correspondants augmentent pendant la dessiccation. Le stockage de ces ARNm codant l'appareil transcriptionnel constitue une étape cruciale pour l'efficacité de la germination de la graine. La quantité de matériel biologique disponible pour ces études étant très limitée, nous avons développé une nouvelle technique de détection des ADNc sur lame de quartz, utilisant la microscopie TIRF. Cette méthode augmente la résolution (elle permet la détection de molécules uniques) et diminue considérablement la quantité de matériel nécessaire à l'hybridation. Finalement, nous avons analysé les conditions sous lesquelles se déroule la photosynthèse embryonnaire. Ces études ont montré que la photosynthèse dans l'embryon se déroule dans un environnement particulier, hypoxique, et sous un éclairement enrichi en longueurs d'onde vertes. Cependant, la structure et le fonctionnement de l'appareil photosynthétique sont semblables à ceux d'une feuille. Nous avons également montré que l'étape transitoire de la photosynthèse embryonnaire est indispensable à la vigueur germinative des graines. Les résultats obtenus lors de ce travail apportent de nouvelles informations sur le fonctionnement de la transcription plastidiale au cours de la formation de la graine. L'importance de l'accumulation d'ARNm, de certaines protéines ainsi que celle de la photosynthèse embryonnaire dans la vigueur germinative ont été soulignées. Ces données permettent de comprendre comment l'efficacité de la germination est conditionnée par la phase de formation de la graine

Characterisation of gene expression in photoheterotrophic plastid during seed formation

L'expression du génome plastidial, un des trois génomes (nucléaire, mitochondrial et plastidial) qui coexistent dans les cellules végétales, est assurée par trois ARN polymérases. Deux NEP (Nuclear-Encoded RNA Polymerase) transcrivent la plupart des gènes de ménage tandis que la PEP (Plastid-Encoded RNA Polymerase) transcrit principalement les gènes liés à la fonction photosynthétique en s'associant à des facteurs de transcription d'origine nucléaire (facteurs sigma) importés dans le plaste. De précédents travaux dans l'équipe ont montré que, contrairement aux observations généralement admises, les trois ARN polymérases sont nécessaires pour assurer une germination efficace des graines d'Arabidopsis. L'objectif de notre travail est de comprendre comment ces enzymes ont été mises en place au cours de la formation de la graine. Pour cela, nous avons analysé l'expression de l'appareil transcriptionnel et du transcriptome plastidial durant les trois phases de formation de la graine d'Arabidopsis thaliana, c'est à dire l'embryogenèse, la maturation (phase photosynthétique) et la dessiccation. L'expression globale du transcriptome plastidial montre que les changements quantitatifs des transcrits sont les plus élevés pour les transcrits des gènes liés à la fonction photosynthétique. Ils sont très fortement exprimés pendant la phase de la maturation et diminuent ensuite, comme leurs protéines correspondantes. Nous observons également une forte accumulation des protéines codant les NEP et les sous unités de la PEP pendant la période de maturation des graines, suivie d'une forte diminution pendant la dessiccation. Cependant, les ARNm correspondants augmentent pendant la dessiccation. Le stockage de ces ARNm codant l'appareil transcriptionnel constitue une étape cruciale pour l'efficacité de la germination de la graine. La quantité de matériel biologique disponible pour ces études étant très limitée, nous avons développé une nouvelle technique de détection des ADNc sur lame de quartz, utilisant la microscopie TIRF. Cette méthode augmente la résolution (elle permet la détection de molécules uniques) et diminue considérablement la quantité de matériel nécessaire à l'hybridation. Finalement, nous avons analysé les conditions sous lesquelles se déroule la photosynthèse embryonnaire. Ces études ont montré que la photosynthèse dans l'embryon se déroule dans un environnement particulier, hypoxique, et sous un éclairement enrichi en longueurs d'onde vertes. Cependant, la structure et le fonctionnement de l'appareil photosynthétique sont semblables à ceux d'une feuille. Nous avons également montré que l'étape transitoire de la photosynthèse embryonnaire est indispensable à la vigueur germinative des graines. Les résultats obtenus lors de ce travail apportent de nouvelles informations sur le fonctionnement de la transcription plastidiale au cours de la formation de la graine. L'importance de l'accumulation d'ARNm, de certaines protéines ainsi que celle de la photosynthèse embryonnaire dans la vigueur germinative ont été soulignées. Ces données permettent de comprendre comment l'efficacité de la germination est conditionnée par la phase de formation de la graine.Transcription of the plastid genome, one of the three genomes (nuclear, mitochondrial and plastidial) that co-exist in the plant cell, is performed by three ARN polymerases. Two NEPs (Nucleus-Encoded Plastid RNA polymerases) transcribe mainly housekeeping genes and one PEP (plastid-encoded RNA polymerase) transcribes principally photosynthesis related genes. PEP needs transcription factors of the sigma type that are nucleus-encoded. We have previously shown that all three RNA polymerases are present in dry seeds and are necessary for efficient germination. These findings raised the question of how theses RNA polymerases come into the dry seeds and what is the importance of plastid gene expression during seed formation. To answer this question my work consisted in the characterization of plastid gene expression profiles and the expression of the components of the plastid transcriptional machinery during the three phases of seed formation, i. e. embryogenesis, maturation (embryonic photosynthesis) and desiccation. The analysis of global plastid transcriptome patterns shows that mRNAs encoding proteins engaged in photosynthesis show the highest quantitative changes during seed formation. Highest mRNA levels are observed during maturation. During desiccation, photosynthesis related mRNA levels as well as the levels of the corresponding proteins strongly decrease. Concerning the expression of NEP and PEP components, we observe also a peak of protein accumulation during maturation that is followed by a strong diminution of the protein levels. On the other hand, the corresponding mRNAs increase continuously during desiccation. This means that these mRNAs accumulate without being translated. We conclude that the storage of mRNAs coding components of the plastid transcriptional machinery in dry seeds is important for efficient germination. Regarding the limited amount of biological material that is available for these types of studies, we have developed a new method for cDNA analyses on microchips that utilises quartz plates and TIRF microscopy. In this way we can visualise single molecules and the amount of necessary material is considerable diminished. Finally, we have also partially characterized the conditions under which embryonic photosynthesis is performed. These studies show that photosynthesis occurs in a special environment that is characterized by hypoxic atmosphere and green enriched light. However, the structure and functioning of the photosynthetic apparatus in seed chloroplasts seems to be very similar to that of chloroplasts in green leaves. This opens the question of how seed photosynthesis can be efficient. On the other hand we have shown that embryonic photosynthesis is indeed very important for efficient germination. Altogether, results provide new information on the functioning of plastid photosynthesis and transcription during seed formation. They underline the importance of the accumulation of NEP and PEP coding mRNAs in dry seeds. We suggest that embryonic photosynthesis influences seed germination not only by providing reserve compounds but also by producing NEP and PEP proteins. Although the majority of these proteins are degraded during desiccation, traces persist and are stored in dry seeds thus assuring immediate transcription of the plastid genome during imbibition/stratification. Our results explain how efficiency of germination is conditioned during seed formation

Expression du génome plastidial d'Arabidopsis thaliana pendant la formation des graines

Transcription of the plastid genome, one of the three genomes (nuclear, mitochondrial and plastidial) that co-exist in the plant cell, is performed by three ARN polymerases. Two NEPs (Nucleus-Encoded Plastid RNA polymerases) transcribe mainly housekeeping genes and one PEP (plastid-encoded RNA polymerase) transcribes principally photosynthesis related genes. PEP needs transcription factors of the sigma type that are nucleus-encoded. We have previously shown that all three RNA polymerases are present in dry seeds and are necessary for efficient germination. These findings raised the question of how theses RNA polymerases come into the dry seeds and what is the importance of plastid gene expression during seed formation. To answer this question my work consisted in the characterization of plastid gene expression profiles and the expression of the components of the plastid transcriptional machinery during the three phases of seed formation, i. e. embryogenesis, maturation (embryonic photosynthesis) and desiccation. The analysis of global plastid transcriptome patterns shows that mRNAs encoding proteins engaged in photosynthesis show the highest quantitative changes during seed formation. Highest mRNA levels are observed during maturation. During desiccation, photosynthesis related mRNA levels as well as the levels of the corresponding proteins strongly decrease. Concerning the expression of NEP and PEP components, we observe also a peak of protein accumulation during maturation that is followed by a strong diminution of the protein levels. On the other hand, the corresponding mRNAs increase continuously during desiccation. This means that these mRNAs accumulate without being translated. We conclude that the storage of mRNAs coding components of the plastid transcriptional machinery in dry seeds is important for efficient germination. Regarding the limited amount of biological material that is available for these types of studies, we have developed a new method for cDNA analyses on microchips that utilises quartz plates and TIRF microscopy. In this way we can visualise single molecules and the amount of necessary material is considerable diminished. Finally, we have also partially characterized the conditions under which embryonic photosynthesis is performed. These studies show that photosynthesis occurs in a special environment that is characterized by hypoxic atmosphere and green enriched light. However, the structure and functioning of the photosynthetic apparatus in seed chloroplasts seems to be very similar to that of chloroplasts in green leaves. This opens the question of how seed photosynthesis can be efficient. On the other hand we have shown that embryonic photosynthesis is indeed very important for efficient germination. Altogether, results provide new information on the functioning of plastid photosynthesis and transcription during seed formation. They underline the importance of the accumulation of NEP and PEP coding mRNAs in dry seeds. We suggest that embryonic photosynthesis influences seed germination not only by providing reserve compounds but also by producing NEP and PEP proteins. Although the majority of these proteins are degraded during desiccation, traces persist and are stored in dry seeds thus assuring immediate transcription of the plastid genome during imbibition/stratification. Our results explain how efficiency of germination is conditioned during seed formation.L'expression du génome plastidial, un des trois génomes (nucléaire, mitochondrial et plastidial) qui coexistent dans les cellules végétales, est assurée par trois ARN polymérases. Deux NEP (Nuclear-Encoded RNA Polymerase) transcrivent la plupart des gènes de ménage tandis que la PEP (Plastid-Encoded RNA Polymerase) transcrit principalement les gènes liés à la fonction photosynthétique en s'associant à des facteurs de transcription d'origine nucléaire (facteurs sigma) importés dans le plaste. De précédents travaux dans l'équipe ont montré que, contrairement aux observations généralement admises, les trois ARN polymérases sont nécessaires pour assurer une germination efficace des graines d'Arabidopsis. L'objectif de notre travail est de comprendre comment ces enzymes ont été mises en place au cours de la formation de la graine. Pour cela, nous avons analysé l'expression de l'appareil transcriptionnel et du transcriptome plastidial durant les trois phases de formation de la graine d'Arabidopsis thaliana, c'est à dire l'embryogenèse, la maturation (phase photosynthétique) et la dessiccation. L'expression globale du transcriptome plastidial montre que les changements quantitatifs des transcrits sont les plus élevés pour les transcrits des gènes liés à la fonction photosynthétique. Ils sont très fortement exprimés pendant la phase de la maturation et diminuent ensuite, comme leurs protéines correspondantes. Nous observons également une forte accumulation des protéines codant les NEP et les sous unités de la PEP pendant la période de maturation des graines, suivie d'une forte diminution pendant la dessiccation. Cependant, les ARNm correspondants augmentent pendant la dessiccation. Le stockage de ces ARNm codant l'appareil transcriptionnel constitue une étape cruciale pour l'efficacité de la germination de la graine. La quantité de matériel biologique disponible pour ces études étant très limitée, nous avons développé une nouvelle technique de détection des ADNc sur lame de quartz, utilisant la microscopie TIRF. Cette méthode augmente la résolution (elle permet la détection de molécules uniques) et diminue considérablement la quantité de matériel nécessaire à l'hybridation. Finalement, nous avons analysé les conditions sous lesquelles se déroule la photosynthèse embryonnaire. Ces études ont montré que la photosynthèse dans l'embryon se déroule dans un environnement particulier, hypoxique, et sous un éclairement enrichi en longueurs d'onde vertes. Cependant, la structure et le fonctionnement de l'appareil photosynthétique sont semblables à ceux d'une feuille. Nous avons également montré que l'étape transitoire de la photosynthèse embryonnaire est indispensable à la vigueur germinative des graines. Les résultats obtenus lors de ce travail apportent de nouvelles informations sur le fonctionnement de la transcription plastidiale au cours de la formation de la graine. L'importance de l'accumulation d'ARNm, de certaines protéines ainsi que celle de la photosynthèse embryonnaire dans la vigueur germinative ont été soulignées. Ces données permettent de comprendre comment l'efficacité de la germination est conditionnée par la phase de formation de la graine

Photoreceptor-dependent regulation of photoprotection.

International audienceIn photosynthetic organisms, proteins in the light-harvesting complex (LHC) harvest light energy to fuel photosynthesis, whereas photoreceptor proteins are activated by the different wavelengths of the light spectrum to regulate cellular functions. Under conditions of excess light, blue-light photoreceptors activate chloroplast avoidance movements in sessile plants, and blue- and green-light photoreceptors cause motile algae to swim away from intense light. Simultaneously, LHCs switch from light-harvesting mode to energy-dissipation mode, which was thought to be independent of photoreceptor-signaling up until recently. Recent advances, however, indicate that energy dissipation in green algae is controlled by photoreceptors activated by blue and UV-B light, and new molecular links have been established between photoreception and photoprotection

Expression du génome plastidial d'Arabidopsis thaliana pendant la formation des graines

L'expression du génome plastidial, un des trois génomes (nucléaire, mitochondrial et plastidial) qui coexistent dans les cellules végétales, est assurée par trois ARN polymérases. Deux NEP (Nuclear-Encoded RNA Polymerase) transcrivent la plupart des gènes de ménage tandis que la PEP (Plastid-Encoded RNA Polymerase) transcrit principalement les gènes liés à la fonction photosynthétique en s'associant à des facteurs de transcription d'origine nucléaire (facteurs sigma) importés dans le plaste. De précédents travaux dans l'équipe ont montré que, contrairement aux observations généralement admises, les trois ARN polymérases sont nécessaires pour assurer une germination efficace des graines d'Arabidopsis. L'objectif de notre travail est de comprendre comment ces enzymes ont été mises en place au cours de la formation de la graine. Pour cela, nous avons analysé l'expression de l'appareil transcriptionnel et du transcriptome plastidial durant les trois phases de formation de la graine d'Arabidopsis thaliana, c'est à dire l'embryogenèse, la maturation (phase photosynthétique) et la dessiccation. L'expression globale du transcriptome plastidial montre que les changements quantitatifs des transcrits sont les plus élevés pour les transcrits des gènes liés à la fonction photosynthétique. Ils sont très fortement exprimés pendant la phase de la maturation et diminuent ensuite, comme leurs protéines correspondantes. Nous observons également une forte accumulation des protéines codant les NEP et les sous unités de la PEP pendant la période de maturation des graines, suivie d'une forte diminution pendant la dessiccation. Cependant, les ARNm correspondants augmentent pendant la dessiccation. Le stockage de ces ARNm codant l'appareil transcriptionnel constitue une étape cruciale pour l'efficacité de la germination de la graine. La quantité de matériel biologique disponible pour ces études étant très limitée, nous avons développé une nouvelle technique de détection des ADNc sur lame de quartz, utilisant la microscopie TIRF. Cette méthode augmente la résolution (elle permet la détection de molécules uniques) et diminue considérablement la quantité de matériel nécessaire à l'hybridation. Finalement, nous avons analysé les conditions sous lesquelles se déroule la photosynthèse embryonnaire. Ces études ont montré que la photosynthèse dans l'embryon se déroule dans un environnement particulier, hypoxique, et sous un éclairement enrichi en longueurs d'onde vertes. Cependant, la structure et le fonctionnement de l'appareil photosynthétique sont semblables à ceux d'une feuille. Nous avons également montré que l'étape transitoire de la photosynthèse embryonnaire est indispensable à la vigueur germinative des graines. Les résultats obtenus lors de ce travail apportent de nouvelles informations sur le fonctionnement de la transcription plastidiale au cours de la formation de la graine. L'importance de l'accumulation d'ARNm, de certaines protéines ainsi que celle de la photosynthèse embryonnaire dans la vigueur germinative ont été soulignées. Ces données permettent de comprendre comment l'efficacité de la germination est conditionnée par la phase de formation de la graine.Transcription of the plastid genome, one of the three genomes (nuclear, mitochondrial and plastidial) that co-exist in the plant cell, is performed by three ARN polymerases. Two NEPs (Nucleus-Encoded Plastid RNA polymerases) transcribe mainly housekeeping genes and one PEP (plastid-encoded RNA polymerase) transcribes principally photosynthesis related genes. PEP needs transcription factors of the sigma type that are nucleus-encoded. We have previously shown that all three RNA polymerases are present in dry seeds and are necessary for efficient germination. These findings raised the question of how theses RNA polymerases come into the dry seeds and what is the importance of plastid gene expression during seed formation. To answer this question my work consisted in the characterization of plastid gene expression profiles and the expression of the components of the plastid transcriptional machinery during the three phases of seed formation, i. e. embryogenesis, maturation (embryonic photosynthesis) and desiccation. The analysis of global plastid transcriptome patterns shows that mRNAs encoding proteins engaged in photosynthesis show the highest quantitative changes during seed formation. Highest mRNA levels are observed during maturation. During desiccation, photosynthesis related mRNA levels as well as the levels of the corresponding proteins strongly decrease. Concerning the expression of NEP and PEP components, we observe also a peak of protein accumulation during maturation that is followed by a strong diminution of the protein levels. On the other hand, the corresponding mRNAs increase continuously during desiccation. This means that these mRNAs accumulate without being translated. We conclude that the storage of mRNAs coding components of the plastid transcriptional machinery in dry seeds is important for efficient germination. Regarding the limited amount of biological material that is available for these types of studies, we have developed a new method for cDNA analyses on microchips that utilises quartz plates and TIRF microscopy. In this way we can visualise single molecules and the amount of necessary material is considerable diminished. Finally, we have also partially characterized the conditions under which embryonic photosynthesis is performed. These studies show that photosynthesis occurs in a special environment that is characterized by hypoxic atmosphere and green enriched light. However, the structure and functioning of the photosynthetic apparatus in seed chloroplasts seems to be very similar to that of chloroplasts in green leaves. This opens the question of how seed photosynthesis can be efficient. On the other hand we have shown that embryonic photosynthesis is indeed very important for efficient germination. Altogether, results provide new information on the functioning of plastid photosynthesis and transcription during seed formation. They underline the importance of the accumulation of NEP and PEP coding mRNAs in dry seeds. We suggest that embryonic photosynthesis influences seed germination not only by providing reserve compounds but also by producing NEP and PEP proteins. Although the majority of these proteins are degraded during desiccation, traces persist and are stored in dry seeds thus assuring immediate transcription of the plastid genome during imbibition/stratification. Our results explain how efficiency of germination is conditioned during seed formation.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Plastid gene expression during chloroplast differentiation and dedifferentiation into non-photosynthetic plastids during seed formation.

International audienceArabidopsis seed formation is coupled with two plastid differentiation processes. Chloroplast formation starts during embryogenesis and ends with the maturation phase. It is followed by chloroplast dedifferentiation/degeneration that starts at the end of the maturation phase and leads to the presence of small non-photosynthetic plastids in dry seeds. We have analysed mRNA and protein levels of nucleus- and plastid-encoded (NEP and PEP) components of the plastid transcriptional machinery, mRNA and protein levels of some plastid RNA polymerase target genes, changes in plastid transcriptome profiles and mRNA and protein levels of some selected nucleus-encoded plastid-related genes in developing seeds during embryogenesis, maturation and desiccation. As expected, most of the mRNAs and proteins increase in abundance during maturation and decrease during desiccation, when plastids dedifferentiate/degenerate. In contrast, mRNAs and proteins of components of the plastid transcriptional apparatus do not decrease or even still increase during the period of plastid dedifferentiation. Results suggest that proteins of the plastid transcriptional machinery are specifically protected from degradation during the desiccation period and conserved in dry seeds to allow immediate regain of plastid transcriptional activity during stratification/germination. In addition, results reveal accumulation and storage of mRNAs coding for RNA polymerase components and sigma factors in dry seeds. They should provide immediately-to-use templates for translation on cytoplasmic ribosomes in order to enhance RNA polymerase protein levels and to provide regulatory proteins for stored PEP to guaranty efficient plastid genome transcription during germination

Rna isolation from developing arabidopsis thaliana seeds suitable for gene expression analysis

International audienc

Rna isolation from developing arabidopsis thaliana seeds suitable for gene expression analysis

International audienc

An update on the regulation of photosynthesis by thylakoid ion channels and transporters in Arabidopsis.

International audienceIn natural variable environments, plants rapidly adjust photosynthesis for optimal balance between light absorption and utilization. There is increasing evidence suggesting that ion fluxes across the chloroplast thylakoid membrane play an important role in this regulation, by affecting the proton motive force, and consequently photosynthesis and thylakoid membrane ultrastructure. This minireview presents an update on the thylakoid ion channels and transporters characterized in Arabidopsis thaliana as being involved in these processes, as well as an outlook at the evolutionary conservation of their functions in other photosynthetic organisms. This is a contribution to shed light on the thylakoid network of ion fluxes and how they help plants to adjust photosynthesis in variable light environments

Global spectroscopic analysis to study the regulation of the photosynthetic proton motive force: A critical reappraisal

International audienceIn natural variable environments, plants rapidly adjust photosynthesis for optimum balance between photochemistry and photoprotection. These adjustments mainly occur via changes in their proton motive force (pmf). Recent studies based on time resolved analysis of the Electro Chromic Signal (ECS) bandshift of photosynthetic pigments in the model plant Arabidopsis thaliana have suggested an active role of ion fluxes across the thylakoid membranes in the regulation of the pmf. Among the different channels and transporters possibly involved in this phenomenon, we previously identified the TPK3 potassium channel. Plants silenced for TPK3 expression displayed light stress signatures, with reduced Non Photochemical Quenching (NPQ) capacity and sustained anthocyanin accumulation, even at moderate intensities. In this work we re-examined the role of this protein in pmf regulation, starting from the observation that both TPK3 knock-down (TPK3 KD) and WT plants display enhanced anthocyanin accumulation in the light under certain growth conditions, especially in old leaves. We thus compared the pmf features of young "green" (without anthocyanins) and old "red" (with anthocyanins) leaves in both genotypes using a global fit analysis of the ECS. We found that the differences in the ECS profile measured between the two genotypes reflect not only differences in TPK3 expression level, but also a modified photosynthetic activity of stressed red leaves, which are present in a larger amounts in the TPK3 KD plants