RESUMEN
In photosynthetic eukaryotes, thousands of proteins are translated in the cytosol and imported into the chloroplast through the concerted action of two translocons-termed TOC and TIC-located in the outer and inner membranes of the chloroplast envelope, respectively. The degree to which the molecular composition of the TOC and TIC complexes is conserved over phylogenetic distances has remained controversial. Here, we combine transcriptomic, biochemical, and genetic tools in the green alga Chlamydomonas (Chlamydomonas reinhardtii) to demonstrate that, despite a lack of evident sequence conservation for some of its components, the algal TIC complex mirrors the molecular composition of a TIC complex from Arabidopsis thaliana. The Chlamydomonas TIC complex contains three nuclear-encoded subunits, Tic20, Tic56, and Tic100, and one chloroplast-encoded subunit, Tic214, and interacts with the TOC complex, as well as with several uncharacterized proteins to form a stable supercomplex (TIC-TOC), indicating that protein import across both envelope membranes is mechanistically coupled. Expression of the nuclear and chloroplast genes encoding both known and uncharacterized TIC-TOC components is highly coordinated, suggesting that a mechanism for regulating its biogenesis across compartmental boundaries must exist. Conditional repression of Tic214, the only chloroplast-encoded subunit in the TIC-TOC complex, impairs the import of chloroplast proteins with essential roles in chloroplast ribosome biogenesis and protein folding and induces a pleiotropic stress response, including several proteins involved in the chloroplast unfolded protein response. These findings underscore the functional importance of the TIC-TOC supercomplex in maintaining chloroplast proteostasis.
Asunto(s)
Chlamydomonas reinhardtii/metabolismo , Cloroplastos/genética , Complejos Multiproteicos/genética , Proteínas de Plantas/genética , Compartimento Celular , Chlamydomonas reinhardtii/genética , Cloroplastos/metabolismo , Evolución Molecular , Regulación de la Expresión Génica de las Plantas , Complejos Multiproteicos/metabolismo , Proteínas de Plantas/metabolismo , Transporte de Proteínas , Homología de Secuencia de AminoácidoRESUMEN
Symbiotic nitrogen fixation between legumes and rhizobia involves a coordinated expression of many plant and bacterial genes as well as finely tuned metabolic activities of micro- and macrosymbionts. In spite of such complex interactions, symbiotic proficiency remains a resilient process, with host plants apparently capable of compensating for some deficiencies in rhizobia. What controls nodule homeostasis is still poorly understood and probably varies between plant species. In this respect, the promiscuous Sinorhizobium (Ensifer) fredii strain NGR234 has become a model to assess the relative contribution of single gene products to many symbioses. Here, we describe how a deletion in nifQ of NGR234 (strain NGRΔnifQ) makes nodules of Vigna unguiculata, V. radiata, and Macroptilium atropurpureum but not of the mimisoid tree Leucaena leucocephala, purple-red. This peculiar dark-nodule phenotype did not necessarily correlate with a decreased proficiency of NGRΔnifQ but coincided with a 20-fold or more accumulation of coproporphyrin III and uroporphyrin III in V. unguiculata nodules. Porphyrin accumulation was not restricted to plant cells infected with bacteroids but also extended to the nodule cortex. Nodule metal-homeostasis was altered but not sufficiently to prevent assembly and functioning of nitrogenase. Although the role of NifQ in donating molybdenum during assembly of nitrogenase cofactor FeMo-co makes it essential in free-living diazotrophs, our results highlight the dispensability of NifQ in many legume species.
Asunto(s)
Proteínas Bacterianas , Metales , Nitrógeno , Porfirinas , Simbiosis , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Homeostasis , Metales/metabolismo , Nitrógeno/metabolismo , Fijación del Nitrógeno , Porfirinas/metabolismoRESUMEN
Thiamine (vitamin B1) is ubiquitous and essential for cell energy supply in all organisms as a vital metabolic cofactor, known for over a century. In plants, it is established that biosynthesis de novo is taking place predominantly in green tissues and is furthermore limited to plastids. Therefore, transport mechanisms are required to mediate the movement of this polar metabolite from source to sink tissue to activate key enzymes in cellular energy generating pathways but are currently unknown. Similar to thiamine, polyamines are an essential set of charged molecules required for diverse aspects of growth and development, the homeostasis of which necessitates long-distance transport processes that have remained elusive. Here, a yeast-based screen allowed us to identify Arabidopsis (Arabidopsis thaliana) PUT3 as a thiamine transporter. A combination of biochemical, physiological, and genetic approaches permitted us to show that PUT3 mediates phloem transport of both thiamine and polyamines. Loss of function of PUT3 demonstrated that the tissue distribution of these metabolites is altered with growth and developmental consequences. The pivotal role of PUT3 mediated thiamine and polyamine homeostasis in plants, and its importance for plant fitness is revealed through these findings.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas de Transporte de Catión/metabolismo , Poliaminas/metabolismo , Tiamina/metabolismo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Transporte Biológico , Proteínas de Transporte de Catión/genética , Floema/genética , Floema/metabolismo , Raíces de Plantas/genética , Raíces de Plantas/metabolismo , Brotes de la Planta/genética , Brotes de la Planta/metabolismo , Plantas Modificadas Genéticamente , Saccharomyces cerevisiae/genéticaRESUMEN
Plastid protein homeostasis is critical during chloroplast biogenesis and responses to changes in environmental conditions. Proteases and molecular chaperones involved in plastid protein quality control are encoded by the nucleus except for the catalytic subunit of ClpP, an evolutionarily conserved serine protease. Unlike its Escherichia coli ortholog, this chloroplast protease is essential for cell viability. To study its function, we used a recently developed system of repressible chloroplast gene expression in the alga Chlamydomonas reinhardtii. Using this repressible system, we have shown that a selective gradual depletion of ClpP leads to alteration of chloroplast morphology, causes formation of vesicles, and induces extensive cytoplasmic vacuolization that is reminiscent of autophagy. Analysis of the transcriptome and proteome during ClpP depletion revealed a set of proteins that are more abundant at the protein level, but not at the RNA level. These proteins may comprise some of the ClpP substrates. Moreover, the specific increase in accumulation, both at the RNA and protein level, of small heat shock proteins, chaperones, proteases, and proteins involved in thylakoid maintenance upon perturbation of plastid protein homeostasis suggests the existence of a chloroplast-to-nucleus signaling pathway involved in organelle quality control. We suggest that this represents a chloroplast unfolded protein response that is conceptually similar to that observed in the endoplasmic reticulum and in mitochondria.
RESUMEN
Reversible protein phosphorylation plays a major role in the acclimation of the photosynthetic apparatus to changes in light. Two paralogous kinases phosphorylate subsets of thylakoid membrane proteins. STATE TRANSITION7 (STN7) phosphorylates LHCII, the light-harvesting antenna of photosystem II (PSII), to balance the activity of the two photosystems through state transitions. STN8, which is mainly involved in phosphorylation of PSII core subunits, influences folding of the thylakoid membranes and repair of PSII after photodamage. The rapid reversibility of these acclimatory responses requires the action of protein phosphatases. In a reverse genetic screen, we identified the chloroplast PP2C phosphatase, PHOTOSYSTEM II CORE PHOSPHATASE (PBCP), which is required for efficient dephosphorylation of PSII proteins. Its targets, identified by immunoblotting and mass spectrometry, largely coincide with those of the kinase STN8. The recombinant phosphatase is active in vitro on a synthetic substrate or on isolated thylakoids. Thylakoid folding is affected in the absence of PBCP, while its overexpression alters the kinetics of state transitions. PBCP and STN8 form an antagonistic kinase and phosphatase pair whose substrate specificity and physiological functions are distinct from those of STN7 and the counteracting phosphatase PROTEIN PHOSPHATASE1/THYLAKOID-ASSOCIATED PHOSPHATASE38, but their activities may overlap to some degree.
Asunto(s)
Aclimatación , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Fosfoproteínas Fosfatasas/metabolismo , Complejo de Proteína del Fotosistema II/metabolismo , Proteínas de Arabidopsis/genética , Cloroplastos/metabolismo , Regulación de la Expresión Génica de las Plantas , Luz , Complejos de Proteína Captadores de Luz/metabolismo , Datos de Secuencia Molecular , Mutación , Fosfoproteínas Fosfatasas/genética , Fosforilación , Proteínas Quinasas/genética , Proteínas Quinasas/metabolismo , Proteína Fosfatasa 2C , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas de las Membranas de los Tilacoides/genética , Proteínas de las Membranas de los Tilacoides/metabolismoRESUMEN
BACKGROUND AND AIMS: Sexual dimorphism, at both the flower and plant level, is widespread in the palm family (Arecaceae), in contrast to the situation in angiosperms as a whole. The tribe Chamaedoreeae is of special interest for studies of the evolution of sexual expression since dioecy appears to have evolved independently twice in this group from a monoecious ancestor. In order to understand the underlying evolutionary pathways, it is important to obtain detailed information on flower structure and development in each of the main clades. METHODS: Dissection and light and scanning electron microscopy were performed on developing flowers of Gaussia attenuata, a neotropical species belonging to one of the three monoecious genera of the tribe. KEY RESULTS: Like species of the other monoecious genera of the Chamaedoreeae (namely Hyophorbe and Synechanthus), G. attenuata produces a bisexual flower cluster known as an acervulus, consisting of a row of male flowers with a basal female flower. Whereas the sterile androecium of female flowers terminated its development at an early stage of floral ontogeny, the pistillode of male flowers was large in size but with no recognizable ovule, developing for a longer period of time. Conspicuous nectary differentiation in the pistillode suggested a possible role in pollinator attraction. CONCLUSIONS: Gaussia attenuata displays a number of floral characters that are likely to be ancestral to the tribe, notably the acervulus flower cluster, which is conserved in the other monoecious genera and also (albeit in a unisexual male form) in the dioecious genera (Wendlandiella and a few species of Chamaedorea). Comparison with earlier data from other genera suggests that large nectariferous pistillodes and early arrest in staminode development might also be regarded as ancestral characters in this tribe.
Asunto(s)
Arecaceae/crecimiento & desarrollo , Flores/crecimiento & desarrollo , Arecaceae/anatomía & histología , Arecaceae/genética , Evolución Biológica , Flores/anatomía & histología , Flores/genética , Microscopía Electrónica de Rastreo , Óvulo Vegetal/anatomía & histología , Óvulo Vegetal/genética , Óvulo Vegetal/crecimiento & desarrollo , Filogenia , Reproducción , Especificidad de la EspecieRESUMEN
Vitamin B6 is an essential nutrient in the human diet derived primarily from plant sources. While it is well established as a cofactor for numerous metabolic enzymes, more recently, vitamin B6 has been implicated as a potent antioxidant. The de novo vitamin B6 biosynthesis pathway in plants has recently been unraveled and involves only two proteins, PDX1 and PDX2. To provide more insight into the effect of the compound on plant development and its role as an antioxidant, we have overexpressed the PDX proteins in Arabidopsis, generating lines with considerably higher levels of the vitamin in comparison with other recent attempts to achieve this goal. Interestingly, it was possible to increase the level of only one of the two catalytically active PDX1 proteins at the protein level, providing insight into the mechanism of vitamin B6 homeostasis in planta. Vitamin B6 enhanced lines have considerably larger vegetative and floral organs and although delayed in pre-reproductive development, do not have an altered overall morphology. The vitamin was observed to accumulate in seeds and the enhancement of its levels was correlated with an increase in their size and weight. This phenotype is predominantly a consequence of embryo enlargement as reflected by larger cells. Furthermore, plants that overaccumulate the vitamin have an increased tolerance to oxidative stress providing in vivo evidence for the antioxidant functionality of vitamin B6. In particular, the plants show an increased resistance to paraquat and photoinhibition, and they attenuate the cell death response observed in the conditional flu mutant.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Transferasas de Grupos Nitrogenados/metabolismo , Estrés Oxidativo , Vitamina B 6/metabolismo , Antioxidantes/metabolismo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Liasas de Carbono-Nitrógeno , Regulación de la Expresión Génica de las Plantas , Metaboloma , Transferasas de Grupos Nitrogenados/genética , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Plantas Modificadas Genéticamente/metabolismo , Semillas/crecimiento & desarrollo , Semillas/metabolismoRESUMEN
Cupriavidus taiwanensis forms proficient symbioses with a few Mimosa species. Inactivation of a type III protein secretion system (T3SS) had no effect on Mimosa pudica but allowed C. taiwanensis to establish chronic infections and fix nitrogen in Leucaena leucocephala. Unlike what was observed for other rhizobia, glutamate rather than plant flavonoids mediated transcriptional activation of this atypical T3SS.
Asunto(s)
Sistemas de Secreción Bacterianos , Cupriavidus/fisiología , Fabaceae/microbiología , Simbiosis , Cupriavidus/metabolismo , Técnicas de Inactivación de Genes , Glutamatos/metabolismo , Proteínas , Transcripción Genética , Activación TranscripcionalRESUMEN
Photosynthetic thylakoid membranes in plants contain highly folded membrane layers enriched in photosystem II, which uses light energy to oxidize water and produce oxygen. The sunlight also causes quantitative phosphorylation of major photosystem II proteins. Analysis of the Arabidopsis thaliana stn7xstn8 double mutant deficient in thylakoid protein kinases STN7 and STN8 revealed light-independent phosphorylation of PsbH protein and greatly reduced N-terminal phosphorylation of D2 protein. The stn7xstn8 and stn8 mutants deficient in light-induced phosphorylation of photosystem II had increased thylakoid membrane folding compared with wild-type and stn7 plants. Significant enhancement in the size of stacked thylakoid membranes in stn7xstn8 and stn8 accelerated gravity-driven sedimentation of isolated thylakoids and was observed directly in plant leaves by transmission electron microscopy. Increased membrane folding, caused by the loss of light-induced protein phosphorylation, obstructed lateral migration of the photosystem II reaction center protein D1 and of processing protease FtsH between the stacked and unstacked membrane domains, suppressing turnover of damaged D1 in the leaves exposed to high light. These findings show that the high level of photosystem II phosphorylation in plants is required for adjustment of macroscopic folding of large photosynthetic membranes modulating lateral mobility of membrane proteins and sustained photosynthetic activity.
Asunto(s)
Arabidopsis/metabolismo , Fotosíntesis , Complejo de Proteína del Fotosistema II/metabolismo , Tilacoides/ultraestructura , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Luz , Microscopía Electrónica de Transmisión , Mutación , Fosforilación , Pliegue de Proteína , Proteínas Quinasas/genética , Proteínas Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas , Tilacoides/metabolismoRESUMEN
Soil flooding is an environmental constraint that is increasingly important for forest ecosystems, affecting tree growth and regeneration. As a result, selection pressure will alter forest diversity and distribution by favouring tree species tolerant of soil oxygen deprivation. Sessile and pedunculate oaks are the most abundant oak species and they exhibit a strong differential tolerance to waterlogging. In order to gain some understanding of the mechanisms of tolerance of both species to hypoxia, we undertook the characterization of the physiological, morphological, cellular and molecular responses of both species to flooding stress. Our results indicate that pedunculate oak, the more tolerant species, succeeded in maintaining its growth, water status and photosynthetic activity at a higher level than sessile oak. Furthermore, pedunculate oak developed aerenchyma in its root cortex as well as adventitious roots. The later exhibited a strong accumulation of class1 non-symbiotic haemoglobin localized by in situ hybridization in the protoderm and in some cortical cells. In conclusion, the higher tolerance of pedunculate oak to flooding was associated with an enhanced capacity to maintain photosynthesis and water homeostasis, coupled with the development of adaptive features (aerenchyma, adventitious roots) and with a higher expression of non-symbiotic haemoglobin in the roots.
Asunto(s)
Adaptación Fisiológica , Hemoglobinas/metabolismo , Proteínas de Plantas/metabolismo , Raíces de Plantas/fisiología , Quercus/fisiología , Estrés Fisiológico , Biomasa , Ecosistema , Inundaciones , Perfilación de la Expresión Génica , Genes de Plantas , Hemoglobinas/genética , Fotoperiodo , Fotosíntesis , Proteínas de Plantas/genética , Raíces de Plantas/anatomía & histología , Raíces de Plantas/genética , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/fisiología , Estomas de Plantas/fisiología , Quercus/genética , Quercus/crecimiento & desarrollo , Agua/metabolismo , Xilema/fisiologíaRESUMEN
Lotus japonicus, a model legume, develops an efficient, nitrogen-fixing symbiosis with Mesorhizobium loti that promotes plant growth. Lotus japonicus also forms functional nodules with Rhizobium sp. NGR234 and R. etli. Yet, in a plant defence-like reaction, nodules induced by R. etli quickly degenerate, thus limiting plant growth. In contrast, nodules containing NGR234 are long-lasting. It was found that NGR234 initiates nodule formation in a similar way to M. loti MAFF303099, but that the nodules which develop on eleven L. japonicus ecotypes are less efficient in fixing nitrogen. Detailed examination of nodulation of L. japonicus cultivar MG-20 revealed that symbiosomes formed four weeks after inoculation by NGR234 are enlarged in comparison with MAFF303099 and contain multiple bacteroids. Nevertheless, nodules formed by NGR234 fix sufficient nitrogen to avoid rejection by the plant. With time, these nodules develop into fully efficient organs containing bacteroids tightly enclosed in symbiosome membranes, just like those formed by M. loti MAFF303099. This work demonstrates the usefulness of using the well-characterized micro-symbiont NGR234 to study symbiotic signal exchange in the later stages of rhizobia-legume symbioses, especially given the large range of bacterial (NGR234) and plant (L. japonicus) mutants that are available.
Asunto(s)
Lotus/crecimiento & desarrollo , Lotus/microbiología , Rhizobium/fisiología , Nódulos de las Raíces de las Plantas/crecimiento & desarrollo , Nódulos de las Raíces de las Plantas/microbiología , Simbiosis , Lotus/citología , Lotus/ultraestructura , Rhizobium/citología , Nódulos de las Raíces de las Plantas/citología , Nódulos de las Raíces de las Plantas/ultraestructuraRESUMEN
Aquaporins (AQPs) belong to the Major Intrinsic Protein family that conducts water and other small solutes across biological membranes. This study aimed to identify and characterize AQP genes in the primary root axis of two oak species, Quercus petraea and Quercus robur. Nine putative AQP genes were cloned, and their expression was profiled in different developmental root zones by real-time PCR. A detailed examination of the predicted amino acid sequences and subsequent phylogenetic analysis showed that the isolated AQPs could be divided into two subfamilies, which included six plasma membrane intrinsic proteins (PIPs) and three tonoplast intrinsic proteins (TIPs). We characterized the anatomical features of the roots and defined three developmental root zones: the immature, transition and mature zones. Expression analysis of the AQPs was performed according to these root developmental stages. Our results showed that the expression of PIP2;3 and TIP1 was significantly higher in Quercus petraea compared with Quercus robur in the three root zones. However, PIP2;1 and TIP2;1 were found to be differentially expressed in the mature zone of the two oak species. Of the nine AQP genes identified and analyzed, we highlighted four genes that might facilitate a deeper understanding of how these two closely related tree species adapted to different environments.
Asunto(s)
Acuaporinas/genética , Raíces de Plantas/genética , Quercus/genética , Secuencia de Aminoácidos , Clonación Molecular , Datos de Secuencia Molecular , Filogenia , Raíces de Plantas/química , Quercus/clasificación , ARN Mensajero/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de AminoácidoRESUMEN
The cellular and molecular adaptations of non-model woody species to environmental changes are still poorly understood. We have cloned and characterised a novel non-symbiotic hemoglobin from oak roots (QpHb1) which exhibits a specific cellular distribution in the root. The QpHb1 gene is strongly expressed in the protoderm and the protoxylem cells in two Quercus species (Q. petraea and Q. robur) with contrasting adaptive potential to drought and flooding. The constitutive expression of QpHb1 in both oak species in specific root tissues combined with the reported presence of nitric oxide in the same tissues and its potential for protein S-nitrosylation could support a role for non-symbiotic hemoglobins in signalling changes in the root environment and/or in controlling some aspects of root development.
RESUMEN
This study presents the isolation and characterization of a novel nonsymbiotic Hb gene from sessile oak (Quercus petraea) seedlings, herein designated QpHb1. The cellular and tissue expression of QpHb1 was analysed by Northern blotting and in situ hybridization. The encoded protein was predicted to consist of 161 amino acid residues, and shares 71 and 51% amino acid sequence identity with the Arabidopsis class 1 and 2 nonsymbiotic Hb, respectively. Northern blot analysis revealed that QpHb1 was strongly expressed in roots. Spatial expression analysis of QpHb1 in the root apical region of sessile oak by in situ hybridization indicated that transcripts were mostly abundant in protoxylem cell initials, some cortical cells and the protoderm. In addition, when comparing the expression profile of QpHb1 in sessile and pedunculate oak (Quercus robur), two species with contrasted hypoxia tolerance, the transcript level of QpHb1 rose early in the most flood-tolerant species, pedunculate oak, during root submergence. The spatial-temporal expression of QpHb1 suggests that this gene could participate in perception and signalling during hypoxia.
Asunto(s)
Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Hemoglobinas/genética , Proteínas de Plantas/genética , Quercus/citología , Quercus/genética , Secuencia de Aminoácidos , Clonación Molecular , Hemoglobinas/metabolismo , Hibridación in Situ , Datos de Secuencia Molecular , Especificidad de Órganos , Oxígeno/metabolismo , Filogenia , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Raíces de Plantas/citología , Raíces de Plantas/genética , Raíces de Plantas/metabolismo , Brotes de la Planta/metabolismo , Quercus/metabolismo , ARN de Planta/genética , ARN de Planta/metabolismo , Agua/metabolismoRESUMEN
The respective distribution of superoxide (O(2) (.-)) and hydrogen peroxide (H(2)O(2)), two reactive oxygen species (ROS) involved in root growth and differentiation, was determined within the Arabidopsis root tip. We investigated the effect of changing the levels of these ROS on root development and the possible interactions with peroxidases. H(2)O(2) was detected by confocal laser-scanning microscopy using hydroxyphenyl fluorescein (HPF). Both O(2) (.-) accumulation and peroxidase distribution were assessed by light microscopy, using nitroblue tetrazolium (NBT) and o-dianisidine, respectively. Root length and root hair length and density were also quantified following ROS scavenging. O(2) (.-) was predominantly located in the apoplast of cell elongation zone, whereas H(2)O(2) accumulated in the differentiation zone and the cell wall of root hairs in formation. Treatments that decrease O(2) (.-) concentration reduced root elongation and root hair formation, while scavenging H(2)O(2) promoted root elongation and suppressed root hair formation. The results allow to precise the respective role of O(2) (.-) and H(2)O(2) in root growth and development. The consequences of their distinct accumulation sites within the root tip are discussed, especially in relation to peroxidases.
Asunto(s)
Arabidopsis/metabolismo , Peróxido de Hidrógeno/metabolismo , Peroxidasas/metabolismo , Raíces de Plantas/metabolismo , Superóxidos/metabolismo , Arabidopsis/enzimología , Arabidopsis/crecimiento & desarrollo , Raíces de Plantas/enzimología , Raíces de Plantas/crecimiento & desarrollo , Plantones/enzimología , Plantones/crecimiento & desarrollo , Plantones/metabolismoRESUMEN
Plastid translational control depends to a large extent on the light conditions, and is presumably mediated by nucleus-encoded proteins acting on organelle gene expression. However, the molecular mechanisms of light signalling involved in translation are still poorly understood. We investigated the role of the Arabidopsis ortholog of Tab2, a nuclear gene specifically required for translation of the PsaB photosystem I subunit in the unicellular alga Chlamydomonas. Inactivation of ATAB2 strongly affects Arabidopsis development and thylakoid membrane biogenesis and leads to an albino phenotype. Moreover the rate of synthesis of the photosystem reaction center subunits is decreased and the association of their mRNAs with polysomes is affected. ATAB2 is a chloroplast A/U-rich RNA-binding protein that presumably functions as an activator of translation with at least two targets, one for each photosystem. During early seedling development, ATAB2 blue-light induction is lowered in photoreceptor mutants, notably in those lacking cryptochromes. Considering its role in protein synthesis and its photoreceptor-mediated expression, ATAB2 represents a novel factor in the signalling pathway of light-controlled translation of photosystem proteins during early plant development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Luz , Complejo de Proteína del Fotosistema I/biosíntesis , Complejo de Proteína del Fotosistema II/biosíntesis , Proteínas de Unión al ARN/metabolismo , Transducción de Señal , Animales , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/genética , Chlamydomonas , Cloroplastos/efectos de la radiación , Cloroplastos/ultraestructura , Exones/genética , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Mutagénesis Insercional , Proteínas Mutantes/metabolismo , Mutación/genética , Fenotipo , Células Fotorreceptoras/metabolismo , Hojas de la Planta/efectos de la radiación , Hojas de la Planta/ultraestructura , Plantas Modificadas Genéticamente , Poli A-U/metabolismo , Polirribosomas/efectos de la radiación , Biosíntesis de Proteínas/efectos de la radiación , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas de Unión al ARN/genética , Plantones/crecimiento & desarrollo , Plantones/efectos de la radiación , Transcripción Genética/efectos de la radiaciónRESUMEN
Proteins of the YidC/Oxa1p/ALB3 family play an important role in inserting proteins into membranes of mitochondria, bacteria, and chloroplasts. In Chlamydomonas reinhardtii, one member of this family, Albino3.1 (Alb3.1), was previously shown to be mainly involved in the assembly of the light-harvesting complex. Here, we show that a second member, Alb3.2, is located in the thylakoid membrane, where it is associated with large molecular weight complexes. Coimmunoprecipitation experiments indicate that Alb3.2 interacts with Alb3.1 and the reaction center polypeptides of photosystem I and II as well as with VIPP1, which is involved in thylakoid formation. Moreover, depletion of Alb3.2 by RNA interference to 25 to 40% of wild-type levels leads to a reduction in photosystems I and II, indicating that the level of Alb3.2 is limiting for the assembly and/or maintenance of these complexes in the thylakoid membrane. Although the levels of several photosynthetic proteins are reduced under these conditions, other proteins are overproduced, such as VIPP1 and the chloroplast chaperone pair Hsp70/Cdj2. These changes are accompanied by a large increase in vacuolar size and, after a prolonged period, by cell death. We conclude that Alb3.2 is required directly or indirectly, through its impact on thylakoid protein biogenesis, for cell survival.
Asunto(s)
Chlamydomonas/citología , Chlamydomonas/metabolismo , Complejo de Proteína del Fotosistema I/metabolismo , Complejo de Proteína del Fotosistema II/metabolismo , Proteínas de Plantas/metabolismo , Animales , Muerte Celular , Supervivencia Celular , Células Cultivadas , Chlamydomonas/ultraestructura , Cloroplastos/metabolismo , Membranas Intracelulares/metabolismo , Datos de Secuencia Molecular , Complejos Multiproteicos/metabolismo , Péptidos/metabolismo , Unión Proteica , Transporte de Proteínas , Interferencia de ARN , Tilacoides/metabolismoRESUMEN
Cells from a green normal (dependent on exogenous hormones) callus and from an achlorophyllous fully habituated (independent from exogenous hormones) callus, both generated from the same sugarbeet strain more than twenty years ago, were reexamined cytologically, ten years after the first comparative description. Cells from the habituated callus, already considered as neoplastic cells, because terminating a neoplastic progression where the organogenic totipotency was lost, still showed nuclear invaginations, polynucleolation, vacuolation of nucleoli and incomplete cell walls, nevertheless at a higher degree. The present study particularly shows that, compared to their previous description, normal cells have started to acquire some features (polynucleolation, nuclear invaginations.) that are typical of the neoplastic cells. This suggests that normal cells, on the long term, also entered a neoplastic progression, which should explain the known progressive loss of regeneration capacity of too long subcultured hormone-dependent calli.