RESUMEN

[This corrects the article DOI: 10.1371/journal.pgen.1010541.].

RESUMEN

Plants often adapt to adverse conditions via differential growth, whereby limited resources are discriminately allocated to optimize the growth of one organ at the expense of another. Little is known about the decision-making processes that underly differential growth. In this study, we developed a screen to identify decision making mutants by deploying two tools that have been used in decision theory: a well-defined yet limited budget, as well as conflict-of-interest scenarios. A forward genetic screen that combined light and water withdrawal was carried out. This identified BRASSINOSTEROID INSENSITIVE 2 (BIN2) alleles as decision mutants with "confused" phenotypes. An assessment of organ and cell length suggested that hypocotyl elongation occurred predominantly via cellular elongation. In contrast, root growth appeared to be regulated by a combination of cell division and cell elongation or exit from the meristem. Gain- or loss- of function bin2 mutants were most severely impaired in their ability to adjust cell geometry in the hypocotyl or cell elongation as a function of distance from the quiescent centre in the root tips. This study describes a novel paradigm for root growth under limiting conditions, which depends not only on hypocotyl-versus-root trade-offs in the allocation of limited resources, but also on an ability to deploy different strategies for root growth in response to multiple stress conditions.

Asunto(s)

Proteínas de Arabidopsis , Arabidopsis , Brasinoesteroides , Plantones , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Hipocótilo , Regulación de la Expresión Génica de las Plantas , Proteínas Quinasas/metabolismo

RESUMEN

Biogenesis of plastid ribosomes is facilitated by auxiliary factors that process and modify ribosomal RNAs (rRNAs) or are involved in ribosome assembly. In comparison with their bacterial and mitochondrial counterparts, the biogenesis of plastid ribosomes is less well understood, and few auxiliary factors have been described so far. In this study, we report the functional characterization of CONSERVED ONLY IN THE GREEN LINEAGE20 (CGL20) in Arabidopsis (Arabidopsis thaliana; AtCGL20), which is a Pro-rich, ∼10-kD protein that is targeted to mitochondria and chloroplasts. In Arabidopsis, CGL20 is encoded by segmentally duplicated genes of high sequence similarity (AtCGL20A and AtCGL20B). Inactivation of these genes in the atcgl20ab mutant led to a visible virescent phenotype and growth arrest at low temperature. The chloroplast proteome, pigment composition, and photosynthetic performance were significantly affected in atcgl20ab mutants. Loss of AtCGL20 impaired plastid translation, perturbing the formation of a hidden break in the 23S rRNA and causing abnormal accumulation of 50S ribosomal subunits in the high-molecular-mass fraction of chloroplast stromal extracts. Moreover, AtCGL20A-eGFP fusion proteins comigrated with 50S ribosomal subunits in Suc density gradients, even after RNase treatment of stromal extracts. Therefore, we propose that AtCGL20 participates in the late stages of the biogenesis of 50S ribosomal subunits in plastids, a role that presumably evolved in the green lineage as a consequence of structural divergence of plastid ribosomes.

Asunto(s)

Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Ribosomas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Cloroplastos/genética , Cloroplastos/metabolismo , Regulación de la Expresión Génica de las Plantas , ARN Ribosómico/genética , ARN Ribosómico/metabolismo , Ribosomas/genética

RESUMEN

Phytochrome A (phyA) mediates different photoresponses what may be connected with the existence of its two types, phyA' and phyA'', differing by spectroscopic, photochemical and functional properties. We investigated a role of phyA phosphorylation in their formation turning to transgenic Arabidopsis thaliana (L. Heynh.) phyA or phyAphyB mutants overexpressing rice wild-type phyA (phyA WT) or mutant phyA (phyA SA) with the first 10 serines substituted by alanines. This prevents phyA phosphorylation at these sites and modifies photoresponses. Etiolated seedlings were employed and phyA parameters were evaluated with the use of low temperature fluorescence spectroscopy and photochemistry. Germination of seeds was induced by white light (WL) pre-treatment for 15min or 3h. Emission spectra of rice phyA WT and phyA SA were similar and their total content was comparable. However, the phyA'/phyA'' proportion in phyA WT was high and varied with the duration of the WL pre-treatment, whereas in phyA SA it was substantially shifted towards phyA'' and did not depend on the pre-illumination. This suggests that phyA SA comprises primarily or exclusively the phyA'' pool and supports the notion that the two phyA types differ by the state of serine phosphorylation. phyA'' was also found to be much more effective in the germination induction than phyA'.

RESUMEN

Senescence is a highly regulated process characterized by the active breakdown of cells, which ultimately leads to the death of plant organs or whole plants. In annual plants such as Arabidopsis thaliana senescence can be observed in each individual leaf. Whether deficiencies in photosynthesis promote the induction of senescence was investigated by monitoring chlorophyll degradation, photosynthetic parameters, and reactive oxygen species accumulation in photosynthetic mutants. Several mutations affecting components of the photosynthetic apparatus, including psal-2, psan-2, and psbs, were found to lead to premature or faster senescence, as did simultaneous inactivation of the STN7 and STN8 kinases. Premature senescence is apparently not directly linked to an overall reduction in photosynthesis but to perturbations in specific aspects of the process. Dark-induced senescence is accelerated in mutants affected in linear electron flow, especially psad2-1, psan-2, and pete2-1, as well as in stn7 and stn8 mutants and STN7 and STN8 overexpressor lines. Interestingly, no direct link with ROS production could be observed.

Asunto(s)

Arabidopsis/metabolismo , Fotosíntesis , Complejo de Proteína del Fotosistema I/metabolismo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Transporte de Electrón , Mutación , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo

RESUMEN

Owing to duplication events in its progenitor, more than 90% of the genes in the Arabidopsis thaliana genome are members of multigene families. A set of 2108 gene families, each consisting of precisely two unlinked paralogous genes, was identified in the nuclear genome of A. thaliana on the basis of sequence similarity. A systematic method for the creation of double knock-out lines for such gene pairs, designated as DUPLO lines, was established and 200 lines are now publicly available. Their initial phenotypic characterisation led to the identification of seven lines with defects that emerge only in the adult stage. A further six lines display seedling lethality and 23 lines were lethal before germination. Another 14 lines are known to show phenotypes under non-standard conditions or at the molecular level. Knock-out of gene pairs with very similar coding sequences or expression profiles is more likely to produce a mutant phenotype than inactivation of gene pairs with dissimilar profiles or sequences. High coding sequence similarity and highly similar expression profiles are only weakly correlated, implying that promoter and coding regions of these gene pairs display different degrees of diversification.

Asunto(s)

Proteínas de Arabidopsis/genética , Arabidopsis/genética , Familia de Multigenes/genética , Alelos , Cartilla de ADN/genética , Duplicación de Gen , Técnicas de Inactivación de Genes , Inflorescencia/genética , Mutación , Sistemas de Lectura Abierta/genética , Fenotipo , Hojas de la Planta/genética , Plantas Modificadas Genéticamente , Plantones/genética , Transcriptoma

RESUMEN

Photoreceptors, especially the far-red light-absorbing phytochrome A, play a crucial role in early seedling development, triggering the transition from etiolated to photomorphogenic growth. Here, we describe the biological functions of two GRAS proteins from Arabidopsis (Arabidopsis thaliana), SCARECROW-LIKE21 (SCL21) and PHYTOCHROME A SIGNAL TRANSDUCTION1 (PAT1), which are specifically involved in phytochrome A signal transduction. Loss-of-function mutants show an elongated hypocotyl under far-red light and are impaired in other far-red high-irradiance responses. The SCL21 transcript itself is down-regulated by far-red light in a phytochrome A- and PAT1-dependent manner. Our results demonstrate that both SCL21 and PAT1 are positive regulators of phytochrome A signal transduction for several high-irradiance responses. Genetic and biochemical evidence suggest a direct interaction of the two proteins.

Asunto(s)

Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas , Fitocromo A/metabolismo , Fitocromo/metabolismo , Transducción de Señal , Secuencia de Aminoácidos , Arabidopsis/genética , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/genética , Núcleo Celular/genética , Núcleo Celular/metabolismo , Epistasis Genética , Prueba de Complementación Genética , Hipocótilo/crecimiento & desarrollo , Hipocótilo/efectos de la radiación , Luz , Datos de Secuencia Molecular , Fenotipo , Fotorreceptores de Plantas/genética , Fotorreceptores de Plantas/metabolismo , Filogenia , Fitocromo/genética , Fitocromo A/genética , Mapeo de Interacción de Proteínas , Interferencia de ARN , ARN Mensajero/genética , ARN Mensajero/metabolismo

RESUMEN

To sense ambient light conditions in order to optimize their growth and development, plants employ a battery of photoreceptors responsive to light quality and quantity. Essential for the sensing of red and far-red (FR) light is the phytochrome family of photoreceptors. Among them, phytochrome A is special because it mediates responses to different light conditions, including both very low fluences (very low fluence response [VLFR]) and high irradiances (high irradiance response [HIR]). In contrast with the FR-HIR signaling pathway, in which several intermediates of the signaling pathway have been identified, specific components of the VLFR pathway remain unknown. Here, we describe owl1 (for orientation under very low fluences of light), a mutant that is specific for the VLFR, suggesting that VLFR and HIR pathways are genetically distinct, although some common mechanisms can be observed. OWL1 codes for a ubiquitous J-domain protein essential for germination, cotyledon opening, hypocotyl elongation, and deviation of the direction of hypocotyl growth from the vertical under very low light conditions. Additionally, we observed a flowering phenotype suggesting a role for the VLFR during the whole life cycle of a plant. OWL1 interacts with the basic helix-loop-helix HFR1 (LONG HYPOCOTYL IN FAR-RED) transcription factor, previously characterized as a component of the FR-HIR pathway. Both proteins are involved in the agravitropic response under FR light. We propose a central function of OWL1 in the VLFR pathway, which is essential for plant survival under unfavorable light conditions.

Asunto(s)

Proteínas de Arabidopsis/fisiología , Arabidopsis/metabolismo , Arabidopsis/efectos de la radiación , Luz , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Unión al ADN/metabolismo , Flores/metabolismo , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Immunoblotting , Datos de Secuencia Molecular , Mutación , Proteínas Nucleares/metabolismo , Hojas de la Planta/metabolismo , Raíces de Plantas/metabolismo , Tallos de la Planta/metabolismo , Unión Proteica , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/genética , Transducción de Señal/efectos de la radiación , Técnicas del Sistema de Dos Híbridos

RESUMEN

The disruption or modulation of signal transduction pathways does not always lead to drastic changes in plant growth and development. Therefore, many loss- or gain-of-function lines do not exhibit an obvious phenotype under normal greenhouse conditions. To be able to assign biological functions to these genes, the mutants need to be evaluated with a broad spectrum of assays to uncover conditional phenotypes.Here we provide an overview on how to evaluate plants in their development and their response to abiotic factors such as light, hormones, and different stressors. The assessment of the behavior of a plant under these conditions can be used to correlate a biological role with a genotype. This phenotypic analysis can be used for profiling of mutants.

Asunto(s)

Arabidopsis/genética , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Reguladores del Crecimiento de las Plantas/farmacología , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Frío , Regulación del Desarrollo de la Expresión Génica/efectos de la radiación , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Genotipo , Calor , Luz , Fenotipo

RESUMEN

With the completion of the Arabidopsis thaliana genome sequencing project the next major challenge is the assignment of biological functions to the more than 25,000 genes. Reverse genetics is a powerful tool to elucidate gene function in Arabidopsis. Increasingly sophisticated genetic approaches are being developed for reverse genetics with the long-term goal of understanding how the coordinated activity of all proteins rises to a complex organism. Identification of a biological function for each gene is often doomed to fail as many loss- or gain-of-function lines exhibit no obvious phenotypes under normal propagation conditions . Here we provide an overview on how to phenotype plants during their development. This phenotypic streamlined analysis is based on a series of defined growth stages (germination, seedling, vegetative, and reproductive stages), which can be used for the profiling of mutants.

Asunto(s)

Arabidopsis/crecimiento & desarrollo , Arabidopsis/genética , Eliminación de Gen , Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas , Fenotipo , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Plantas Modificadas Genéticamente/metabolismo

RESUMEN

The phytochrome (phy)A and phyB photoreceptors mediate three photobiological response modes in plants; whereas phyA can mediate the very-low-fluence response (VLFR), the high-irradiance response (HIR) and, to some extent, the low fluence response (LFR), phyB and other type II phytochromes only mediate the LFR. To investigate to what level a rice phyA can complement for Arabidopsis phyA or phyB function and to evaluate the role of the serine residues in the first 20 amino acids of the N-terminus of phyA, we examined VLFR, LFR, and HIR responses in phyB and phyAphyB mutant plants transformed with rice PHYA cDNA or a mutant rice PHYA cDNA in which the first 10 serine residues were mutated to alanines (phyA SA). Utilizing mutants without endogenous phyB allowed the evaluation of red-light-derived responses sensed by the rice phyA. In summary, the WT rice phyA could complement VLFR and LFR responses such as inhibition of hypocotyl elongation under pulses of FR or continuous R light, induction of flowering and leaf expansion, whereas the phyA SA was more specific for HIR responses (e.g. inhibition of hypocotyl elongation and anthocyanin accumulation under continuous far-red light). As the N-terminal serines can no longer be phosphorylated in the phyA SA mutant, this suggests a role for phosphorylation discriminating between the different phyA-dependent responses. The efficacy of the rice phyA expressed in Arabidopsis was dependent upon the developmental age of the plants analyzed and on the physiological response, suggesting a stage-dependent downstream modulation of phytochrome signaling.

Asunto(s)

Arabidopsis/genética , Luz , Oryza/genética , Fitocromo A/genética , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/efectos de la radiación , Cotiledón/genética , Cotiledón/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Regulación de la Expresión Génica de las Plantas , Germinación/genética , Hipocótilo/efectos de la radiación , Datos de Secuencia Molecular , Mutación , Fosforilación , Fitocromo A/química , Fitocromo A/metabolismo , Fitocromo A/efectos de la radiación , Fitocromo B/química , Fitocromo B/genética , Fitocromo B/efectos de la radiación , Alineación de Secuencia , Homología de Secuencia de Aminoácido

RESUMEN

Phytochrome photoreceptors enable plants to perceive divergent light signals leading to adaptive changes in response to differing environmental conditions. However, the mechanism of light signal transduction is not fully understood. Here we report the identification of a new signaling intermediate from Arabidopsis thaliana, Scarecrow-like (SCL)13, which serves as a positive regulator of continuous red light signals downstream of phytochrome B (phyB). SCL13 antisense lines exhibit reduced sensitivity towards red light, but only a distinct subset of phyB-mediated responses is affected, indicating that SCL13 executes its major role in hypocotyl elongation during de-etiolation. Genetic evidence suggests that SCL13 is also needed to modulate phytochrome A (phyA) signal transduction in a phyB-independent way. The SCL13 protein is localized in the cytoplasm, but can also be detected in the nucleus. Overexpression of both a nuclear and cytoplasmic localized SCL13 protein leads to a hypersensitive phenotype under red light indicating that SCL13 is biologically active in both compartments. SCL13 is a member of the plant-specific GRAS protein family, which is involved in various different developmental and signaling pathways. A previously identified phytochrome A signaling intermediate, PAT1, belongs to the same subbranch of GRAS proteins as SCL13. Although both proteins are involved in phytochrome signaling, each is specific for a different light condition and regulates a different subset of responses.

Asunto(s)

Proteínas de Arabidopsis/metabolismo , Arabidopsis/efectos de la radiación , Fitocromo A/metabolismo , Transducción de Señal/fisiología , Secuencia de Aminoácidos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Núcleo Celular/metabolismo , Citoplasma/metabolismo , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas/fisiología , Germinación , Hipocótilo/genética , Hipocótilo/crecimiento & desarrollo , Luz , Datos de Secuencia Molecular , Fitocromo/genética , Fitocromo/metabolismo , Fitocromo B/metabolismo , Plantas Modificadas Genéticamente , ARN de Planta/genética , Homología de Secuencia de Aminoácido

RESUMEN

GRAS proteins are a recently discovered family of plant-specific proteins named after GAI, RGA and SCR, the first three of its members isolated. Although the Arabidopsis genome encodes at least 33 GRAS protein family members only a few GRAS proteins have been characterized so far. However, it is becoming clear that GRAS proteins exert important roles in very diverse processes such as signal transduction, meristem maintenance and development. Here we present a survey of the different GRAS proteins and review the current knowledge of the function of individual members of this protein family.

Asunto(s)

Arabidopsis/fisiología , Proteínas de Plantas/fisiología , Transducción de Señal/fisiología , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/fisiología , Mutación , Filogenia , Proteínas de Plantas/genética , Transducción de Señal/genética , Factores de Transcripción/genética , Factores de Transcripción/fisiología

RESUMEN

Far-red light regulates many aspects of seedling development, such as inhibition of hypocotyl elongation and the promotion of greening, acting in part through phytochrome A (phyA). The RING motif protein COP1 is also important because cop1 mutants exhibit constitutive photomorphogenesis in darkness. COP1 is present in the nucleus in darkness but is gradually relocated to the cytoplasm upon illumination. Here we show that COP1 functions as an E3 ligase ubiquitinating both itself and the myb transcription activator LAF1, which is required for complete phyA responses. In transgenic plants, inducible COP1 overexpression leads to a decrease in LAF1 concentrations, but is blocked by the proteasome inhibitor MG132. The coiled-coil domain of SPA1, a negative regulator of phyA signalling, has no effect on COP1 auto-ubiquitination but facilitates LAF1 ubiquitination at low COP1 concentrations. These results indicate that, in darkness, COP1 functions as a repressor of photomorphogenesis by promoting the ubiquitin-mediated proteolysis of a subset of positive regulators, including LAF1. After the activation of phyA, SPA1 stimulates the E3 activity of residual nuclear COP1 to ubiquitinate LAF1, thereby desensitizing phyA signals.

Asunto(s)

Proteínas de Arabidopsis/fisiología , Proteínas Nucleares/fisiología , Transactivadores/fisiología , Ubiquitina/metabolismo , Secuencias de Aminoácidos , Ligasas/metabolismo , Morfogénesis , Fotoquímica , Fitocromo/fisiología , Fitocromo A , Plantas Modificadas Genéticamente , Proteínas Recombinantes de Fusión/metabolismo , Ubiquitina-Proteína Ligasas