RESUMEN
Plant BZR1-BAM transcription factors contain a ß-amylase (BAM)-like domain, characteristic of proteins involved in starch breakdown. The enzyme-derived domains appear to be noncatalytic, but they determine the function of the two Arabidopsis thaliana BZR1-BAM isoforms (BAM7 and BAM8) during transcriptional initiation. Removal or swapping of the BAM domains demonstrates that the BAM7 BAM domain restricts DNA binding and transcriptional activation, while the BAM8 BAM domain allows both activities. Furthermore, we demonstrate that BAM7 and BAM8 interact on the protein level and cooperate during transcriptional regulation. Site-directed mutagenesis of residues in the BAM domain of BAM8 shows that its function as a transcriptional activator is independent of catalysis but requires an intact substrate binding site, suggesting it may bind a ligand. Microarray experiments with plants overexpressing truncated versions lacking the BAM domain indicate that the pseudo-enzymatic domain increases selectivity for the preferred cis-regulatory element BBRE (BZR1-BAM Responsive Element). Side specificity toward the G-box may allow crosstalk to other signaling networks. This work highlights the importance of the enzyme-derived domain of BZR1-BAMs, supporting their potential role as metabolic sensors.
RESUMEN
Environmental stress often leads to an increased production of reactive oxygen species that are involved in plastid-to-nucleus retrograde signaling. Soon after the release of singlet oxygen ((1)O(2)) in chloroplasts of the flu mutant of Arabidopsis, reprogramming of nuclear gene expression reveals a rapid transfer of signals from the plastid to the nucleus. We have identified extraplastidic signaling constituents involved in (1)O(2)-initiated plastid-to-nucleus signaling and nuclear gene activation after mutagenizing a flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second-site mutations that lead to a constitutive up-regulation of the reporter gene or abrogate its (1)O(2)-dependent up-regulation. One of these mutants, caa39, turned out to be a weak mutant allele of the Topoisomerase VI (Topo VI) A-subunit gene with a single amino acid substitution. Transcript profile analysis of flu and flu caa39 mutants revealed that Topo VI is necessary for the full activation of AAA-ATPase and a set of (1)O(2)-responsive transcripts in response to (1)O(2). Topo VI binds to the promoter of the AAA-ATPase and other (1)O(2)-responsive genes, and hence could directly regulate their expression. Under photoinhibitory stress conditions, which enhance the production of (1)O(2) and H(2)O(2), Topo VI regulates (1)O(2)-responsive and H(2)O(2)-responsive genes in a distinct manner. These results suggest that Topo VI acts as an integrator of multiple signals generated by reactive oxygen species formed in plants under adverse environmental conditions.
Asunto(s)
Arabidopsis/enzimología , Proteínas Arqueales/metabolismo , ADN-Topoisomerasas de Tipo II/metabolismo , Regulación de la Expresión Génica de las Plantas/fisiología , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/fisiología , Estrés Fisiológico/fisiología , Proteínas de Arabidopsis/genética , Núcleo Celular/metabolismo , Inmunoprecipitación de Cromatina , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas/genética , Luciferasas , Análisis por Micromatrices , Mutación/genética , Plastidios/metabolismo , Reacción en Cadena en Tiempo Real de la Polimerasa , Oxígeno Singlete/metabolismoRESUMEN
Plants contain ß-amylase-like proteins (BAMs; enzymes usually associated with starch breakdown) present in the nucleus rather than targeted to the chloroplast. They possess BRASSINAZOLE RESISTANT1 (BZR1)-type DNA binding domains--also found in transcription factors mediating brassinosteroid (BR) responses. The two Arabidopsis thaliana BZR1-BAM proteins (BAM7 and BAM8) bind a cis-regulatory element that both contains a G box and resembles a BR-responsive element. In protoplast transactivation assays, these BZR1-BAMs activate gene expression. Structural modeling suggests that the BAM domain's glucan binding cleft is intact, but the recombinant proteins are at least 1000 times less active than chloroplastic ß-amylases. Deregulation of BZR1-BAMs (the bam7bam8 double mutant and BAM8-overexpressing plants) causes altered leaf growth and development. Of the genes upregulated in plants overexpressing BAM8 and downregulated in bam7bam8 plants, many carry the cis-regulatory element in their promoters. Many genes that respond to BRs are inversely regulated by BZR1-BAMs. We propose a role for BZR1-BAMs in controlling plant growth and development through crosstalk with BR signaling. Furthermore, we speculate that BZR1-BAMs may transmit metabolic signals by binding a ligand in their BAM domain, although diurnal changes in the concentration of maltose, a candidate ligand produced by chloroplastic ß-amylases, do not influence their transcription factor function.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Arabidopsis/crecimiento & desarrollo , Brotes de la Planta/crecimiento & desarrollo , Factores de Transcripción/metabolismo , beta-Amilasa/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/química , Secuencia de Bases , Regulación de la Expresión Génica de las Plantas , Genes de Plantas/genética , Glucanos/metabolismo , Hidrólisis , Modelos Biológicos , Datos de Secuencia Molecular , Proteínas Mutantes/aislamiento & purificación , Proteínas Mutantes/metabolismo , Mutación/genética , Proteínas Nucleares/metabolismo , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Brotes de la Planta/enzimología , Unión Proteica , Estructura Terciaria de Proteína , Elementos de Respuesta/genética , Transactivadores/metabolismo , Factores de Transcripción/química , beta-Amilasa/químicaRESUMEN
Retrograde plastid-to-nucleus signaling tightly controls and coordinates the nuclear and plastid gene expression that is required for plastid biogenesis and chloroplast activity. As chloroplasts act as sensors of environmental changes, plastid-derived signaling also modulates stress responses of plants by transferring stress-related signals and altering nuclear gene expression. Various mutant screens have been undertaken to identify constituents of plastid signaling pathways. Almost all mutations identified in these screens target plastid-specific but not extraplastidic functions. They have been suggested to define either genuine constituents of retrograde signaling pathways or components required for the synthesis of plastid signals. Here we report the characterization of the constitutive activator of AAA-ATPase (caa33) mutant, which reveals another way of how mutations that affect plastid functions may modulate retrograde plastid signaling. caa33 disturbs a plastid-specific function by impeding plastid division, and thereby perturbing plastid homeostasis. This results in preconditioning plants by activating the expression of stress genes, enhancing pathogen resistance and attenuating the capacity of the plant to respond to plastid signals. Our study reveals an intimate link between chloroplast activity and the susceptibility of the plant to stress, and emphasizes the need to consider the possible impact of preconditioning on retrograde plastid-to-nucleus signaling.
Asunto(s)
Aclimatación/fisiología , Proteínas de Arabidopsis/genética , Arabidopsis/fisiología , Núcleo Celular/fisiología , Cloroplastos/fisiología , Transducción de Señal/fisiología , Adenosina Trifosfatasas/genética , Adenosina Trifosfatasas/metabolismo , Adenosina Trifosfato/metabolismo , Alelos , Arabidopsis/enzimología , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Muerte Celular , Núcleo Celular/genética , Cloroplastos/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Homeostasis , Luz , Células del Mesófilo/fisiología , Mutación , Fenotipo , Oxígeno Singlete/metabolismo , Estrés Fisiológico/fisiologíaRESUMEN
Here, we describe the snowy cotyledon3 (sco3-1) mutation, which impairs chloroplast and etioplast development in Arabidopsis thaliana seedlings. SCO3 is a member of a largely uncharacterized protein family unique to the plant kingdom. The sco3-1 mutation alters chloroplast morphology and development, reduces chlorophyll accumulation, impairs thylakoid formation and photosynthesis in seedlings, and results in photoinhibition under extreme CO(2) concentrations in mature leaves. There are no readily apparent changes to chloroplast biology, such as transcription or assembly that explain the disruption to chloroplast biogenesis. Indeed, SCO3 is actually targeted to another organelle, specifically to the periphery of peroxisomes. However, impaired chloroplast development cannot be attributed to perturbed peroxisomal metabolic processes involving germination, fatty acid ß-oxidation or photorespiration, though there are so far undescribed changes in low and high CO(2) sensitivity in seedlings and young true leaves. Many of the chloroplasts are bilobed, and some have persistent membranous extensions that encircle other cellular components. Significantly, there are changes to the cytoskeleton in sco3-1, and microtubule inhibitors have similar effects on chloroplast biogenesis as sco3-1 does. The localization of SCO3 to the periphery of the peroxisomes was shown to be dependent on a functional microtubule cytoskeleton. Therefore, the microtubule and peroxisome-associated SCO3 protein is required for chloroplast development, and sco3-1, along with microtubule inhibitors, demonstrates an unexpected role for the cytoskeleton and peroxisomes in chloroplast biogenesis.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Cloroplastos/fisiología , Citoesqueleto/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Mutagénesis Insercional , Peroxisomas/metabolismo , Filogenia , Hojas de la Planta/crecimiento & desarrollo , Plantones/crecimiento & desarrolloRESUMEN
Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts, changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Extensive genetic screens aimed at identifying constituents involved in (1)O(2)-mediated plastid-to-nucleus signaling have failed to identify extraplastidic signaling components. This finding suggests that (1)O(2)-mediated signals are not translocated to the nucleus via a single linear pathway, but rather through a signaling network that is difficult to block by single mutations. The complexity of this signaling network has been tackled by mutagenizing a transgenic flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second site mutants that constitutively express the reporter gene at a high level. One of the mutants was shown by map-based cloning and sequencing to contain a single amino acid change in the PLEIOTROPIC RESPONSE LOCUS 1 (PRL1) protein. PRL1 suppresses the expression of AAA-ATPase and other (1)O(2)-responsive genes. PRL1 seems to play a major role in modulating responses of plants to environmental changes by interconnecting (1)O(2)-mediated retrograde signaling with other signaling pathways.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas Portadoras/metabolismo , Proteínas Nucleares/metabolismo , Transducción de Señal , Oxígeno Singlete/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas Portadoras/genética , Clonación Molecular , Regulación de la Expresión Génica de las Plantas , Prueba de Complementación Genética , Mutagénesis , Proteínas Nucleares/genética , Complejo de Proteína del Fotosistema II , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , ARN de Planta/genética , Estrés FisiológicoRESUMEN
Shortly after the release of singlet oxygen ((1)O(2)) in chloroplasts drastic changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Factors involved in this retrograde signaling were identified by mutagenizing a transgenic flu line expressing a (1)O(2)-responsive reporter gene. The reporter gene consisted of the luciferase open reading frame and the promoter of an AAA-ATPase gene (At3g28580) that was selectively activated by (1)O(2) but not by superoxide or hydrogen peroxide. A total of eight second-site mutants were identified that either constitutively activate the reporter gene and the endogenous AAA-ATPase irrespectively of whether (1)O(2) was generated or not (constitutive activators of AAA-ATPase, caa) or abrogated the (1)O(2)-dependent up-regulation of these genes as seen in the transgenic parental flu line (non-activators of AAA-ATPase, naa). The characterization of the mutants strongly suggests that (1)O(2)-signaling does not operate as an isolated linear pathway but rather forms an integral part of a signaling network that is modified by other signaling routes and impacts not only stress responses of plants but also their development.
Asunto(s)
Arabidopsis/genética , Mutación , Transducción de Señal/fisiología , Oxígeno Singlete/metabolismo , Adaptación Fisiológica/genética , Adaptación Fisiológica/fisiología , Adenosina Trifosfatasas/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Peróxido de Hidrógeno/farmacología , Luciferasas/genética , Luciferasas/metabolismo , Oxidantes/farmacología , Plantas Modificadas Genéticamente , Regiones Promotoras Genéticas/genética , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Rosa Bengala/farmacología , Transducción de Señal/genéticaRESUMEN
Undoubtedly, biotechnology has a tremendous impact on our daily lives. As a result of this and in parallel to the advancement of knowledge in this field of applied research, consumer awareness of the potential benefits and risks of this technology has steadily increased, leading to a thorough investigation of the public perception of biotechnology in the past years. Indeed, it has become clear that it is in the general interest of science and especially of applied research to inform the public of its advances. A promising next step is to strengthen biotechnology communication in scholastic institutions. In this paper, we investigate the perception of biotechnology in a specific target group, namely high-school students in the 16-20-year-old age range. We conducted a questionnaire-based survey on a total of 1410 students in six European countries to investigate students' perception, concern, scientific knowledge, and awareness. Our data revealed some unexpected patterns of acceptance and concern about biotechnology. Knowledge analysis indicated that pupils lack specific knowledge about biotechnological applications and their interest in biotechnology appeared to be linked to knowledge. Analysis of specific questions about teaching practices at schools suggests that a better targeted choice in media as vehicles for information together with selected speakers could be instrumental in increasing students' interest in science and more specifically in biotechnology.