RESUMEN
Proteolysis, including post-translational proteolytic processing as well as protein degradation and amino acid recycling, is an essential component of the growth and development of living organisms. In this article, experts in plant proteolysis pose and discuss compelling open questions in their areas of research. Topics covered include the role of proteolysis in the cell cycle, DNA damage response, mitochondrial function, the generation of N-terminal signals (degrons) that mark many proteins for degradation (N-terminal acetylation, the Arg/N-degron pathway, and the chloroplast N-degron pathway), developmental and metabolic signaling (photomorphogenesis, abscisic acid and strigolactone signaling, sugar metabolism, and postharvest regulation), plant responses to environmental signals (endoplasmic-reticulum-associated degradation, chloroplast-associated degradation, drought tolerance, and the growth-defense trade-off), and the functional diversification of peptidases. We hope these thought-provoking discussions help to stimulate further research.
Asunto(s)
Proteínas de Plantas , Plantas , Proteolisis , Proteínas de Plantas/metabolismo , Proteínas de Plantas/genética , Plantas/metabolismo , Plantas/genética , Transducción de Señal , Procesamiento Proteico-PostraduccionalRESUMEN
In Arabidopsis (Arabidopsis thaliana), the F-box protein F-BOX-LIKE17 (FBL17) was previously identified as an important cell-cycle regulatory protein. FBL17 is required for cell division during pollen development and for normal cell-cycle progression and endoreplication during the diploid sporophyte phase. FBL17 was reported to control the stability of the CYCLIN-DEPENDENT KINASE inhibitor KIP-RELATED PROTEIN (KRP), which may underlie the drastic reduction in cell division activity in both shoot and root apical meristems observed in fbl17 loss-of-function mutants. However, whether FBL17 has other substrates and functions besides degrading KRPs remains poorly understood. Here we show that mutation of FBL17 leads not only to misregulation of cell cycle genes, but also to a strong upregulation of genes involved in DNA damage and repair processes. This phenotype is associated with a higher frequency of DNA lesions in fbl17 and increased cell death in the root meristem, even in the absence of genotoxic stress. Notably, the constitutive activation of DNA damage response genes is largely SOG1-independent in fbl17 In addition, through analyses of root elongation, accumulation of cell death, and occurrence of γH2AX foci, we found that fbl17 mutants are hypersensitive to DNA double-strand break-induced genotoxic stress. Notably, we observed that the FBL17 protein is recruited at nuclear foci upon double-strand break induction and colocalizes with γH2AX, but only in the presence of RETINOBLASTOMA RELATED1. Altogether, our results highlight a role for FBL17 in DNA damage response, likely by ubiquitylating proteins involved in DNA-damage signaling or repair.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Daño del ADN , ADN de Plantas/metabolismo , Proteínas F-Box/metabolismo , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Bleomicina/farmacología , Núcleo Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Roturas del ADN de Doble Cadena/efectos de los fármacos , Reparación del ADN/efectos de los fármacos , Reparación del ADN/genética , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Mutación/genética , Factores de Transcripción/metabolismo , Transcriptoma/genética , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/genéticaRESUMEN
Due to their sessile lifestyle, plants are especially exposed to various stresses, including genotoxic stress, which results in altered genome integrity. Upon the detection of DNA damage, distinct cellular responses lead to cell cycle arrest and the induction of DNA repair mechanisms. Interestingly, it has been shown that some cell cycle regulators are not only required for meristem activity and plant development but are also key to cope with the occurrence of DNA lesions. In this review, we first summarize some important regulatory steps of the plant cell cycle and present a brief overview of the DNA damage response (DDR) mechanisms. Then, the role played by some cell cycle regulators at the interface between the cell cycle and DNA damage responses is discussed more specifically.
Asunto(s)
Ciclo Celular , Daño del ADN , ADN de Plantas/metabolismo , Plantas/metabolismo , ADN de Plantas/genética , Plantas/genéticaRESUMEN
The plant cell cycle is tightly regulated by factors that integrate endogenous cues and environmental signals to adapt plant growth to changing conditions. Under drought, cell division in young leaves is blocked by an active mechanism, reducing the evaporative surface and conserving energy resources. The molecular function of cyclin-dependent kinase-inhibitory proteins (CKIs) in regulating the cell cycle has already been well studied, but little is known about their involvement in cell cycle regulation under adverse growth conditions. In this study, we show that the transcript of the CKI gene SIAMESE-RELATED1 (SMR1) is quickly induced under moderate drought in young Arabidopsis (Arabidopsis thaliana) leaves. Functional characterization further revealed that SMR1 inhibits cell division and affects meristem activity, thereby restricting the growth of leaves and roots. Moreover, we demonstrate that SMR1 is a short-lived protein that is degraded by the 26S proteasome after being ubiquitinated by a Cullin-RING E3 ubiquitin ligase. Consequently, overexpression of a more stable variant of the SMR1 protein leads to a much stronger phenotype than overexpression of the native SMR1. Under moderate drought, both the SMR1 transcript and SMR1 protein accumulate. Despite this induction, smr1 mutants do not show overall tolerance to drought stress but do show less growth inhibition of young leaves under drought. Surprisingly, the growth-repressive hormone ethylene promotes SMR1 induction, but the classical drought hormone abscisic acid does not.
Asunto(s)
Proteínas de Arabidopsis/genética , Sequías , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Proteínas Nucleares/genética , Hojas de la Planta/genética , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Ciclo Celular/genética , Meristema/genética , Meristema/crecimiento & desarrollo , Meristema/metabolismo , Mutación , Proteínas Nucleares/metabolismo , Fenotipo , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Plantas Modificadas GenéticamenteRESUMEN
A key step of the cell cycle is the entry into the DNA replication phase that typically commits cells to divide. However, little is known about the molecular mechanisms regulating this transition in plants. Here, we investigated the function of FBL17 (F BOX-LIKE17), an Arabidopsis thaliana F-box protein previously shown to govern the progression through the second mitosis during pollen development. Our work reveals that FBL17 function is not restricted to gametogenesis. FBL17 transcripts accumulate in both proliferating and postmitotic cell types of Arabidopsis plants. Loss of FBL17 function drastically reduces plant growth by altering cell division activity in both shoot and root apical meristems. In fbl17 mutant plants, DNA replication is severely impaired and endoreplication is fully suppressed. At the molecular level, lack of FBL17 increases the stability of the CDK (CYCLIN-DEPENDENT KINASE) inhibitor KIP-RELATED PROTEIN2 known to switch off CDKA;1 kinase activity. Despite the strong inhibition of cell proliferation in fbl17, some cells are still able to enter S phase and eventually to divide, but they exhibit a strong DNA damage response and often missegregate chromosomes. Altogether, these data indicate that the F-box protein FBL17 acts as a master cell cycle regulator during the diploid sporophyte phase of the plant.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Diferenciación Celular , Endorreduplicación , Proteínas F-Box/genética , Arabidopsis/citología , Arabidopsis/crecimiento & desarrollo , Arabidopsis/fisiología , Proteínas de Arabidopsis/metabolismo , Ciclo Celular , División Celular , Proteínas Inhibidoras de las Quinasas Dependientes de la Ciclina/genética , Proteínas Inhibidoras de las Quinasas Dependientes de la Ciclina/metabolismo , Replicación del ADN , Proteínas F-Box/metabolismo , Regulación de la Expresión Génica de las Plantas , Meristema/genética , Mitosis , Mutación , Fase SRESUMEN
Phytohormones regulate plant growth from cell division to organ development. Jasmonates (JAs) are signaling molecules that have been implicated in stress-induced responses. However, they have also been shown to inhibit plant growth, but the mechanisms are not well understood. The effects of methyl jasmonate (MeJA) on leaf growth regulation were investigated in Arabidopsis (Arabidopsis thaliana) mutants altered in JA synthesis and perception, allene oxide synthase and coi1-16B (for coronatine insensitive1), respectively. We show that MeJA inhibits leaf growth through the JA receptor COI1 by reducing both cell number and size. Further investigations using flow cytometry analyses allowed us to evaluate ploidy levels and to monitor cell cycle progression in leaves and cotyledons of Arabidopsis and/or Nicotiana benthamiana at different stages of development. Additionally, a novel global transcription profiling analysis involving continuous treatment with MeJA was carried out to identify the molecular players whose expression is regulated during leaf development by this hormone and COI1. The results of these studies revealed that MeJA delays the switch from the mitotic cell cycle to the endoreduplication cycle, which accompanies cell expansion, in a COI1-dependent manner and inhibits the mitotic cycle itself, arresting cells in G1 phase prior to the S-phase transition. Significantly, we show that MeJA activates critical regulators of endoreduplication and affects the expression of key determinants of DNA replication. Our discoveries also suggest that MeJA may contribute to the maintenance of a cellular "stand-by mode" by keeping the expression of ribosomal genes at an elevated level. Finally, we propose a novel model for MeJA-regulated COI1-dependent leaf growth inhibition.
Asunto(s)
Acetatos/farmacología , Arabidopsis/citología , Arabidopsis/genética , Ciclopentanos/farmacología , Endorreduplicación/efectos de los fármacos , Oxilipinas/farmacología , Hojas de la Planta/citología , Hojas de la Planta/crecimiento & desarrollo , Arabidopsis/efectos de los fármacos , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Recuento de Células , Núcleo Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Tamaño del Núcleo Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Tamaño de la Célula/efectos de los fármacos , Análisis por Conglomerados , Cotiledón/efectos de los fármacos , Cotiledón/crecimiento & desarrollo , Replicación del ADN/efectos de los fármacos , ADN de Plantas/metabolismo , Regulación hacia Abajo/efectos de los fármacos , Endorreduplicación/genética , Perfilación de la Expresión Génica , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Meristema/citología , Meristema/efectos de los fármacos , Mitosis/efectos de los fármacos , Mitosis/genética , Modelos Biológicos , Fenotipo , Hojas de la Planta/efectos de los fármacos , Proteínas Ribosómicas/genética , Proteínas Ribosómicas/metabolismoRESUMEN
Root architecture and growth patterns are plant features that are still poorly understood. When grown under in vitro conditions, seedlings with mutations in Arabidopsis thaliana genes MLO4 or MLO11 exhibit aberrant root growth patterns upon contact with hard surfaces, exemplified as tight root spirals. We used a set of physiological assays and genetic tools to characterize this thigmomorphogenic defect in detail. We observed that the mlo4/mlo11-associated root curling phenotype is not recapitulated in a set of mutants with altered root growth patterns or architecture. We further found that mlo4/mlo11-conditioned root curling is not dependent upon light and endogenous flavonoids, but is pH-sensitive and affected by exogenous calcium levels. Based upon the latter two characteristics, mlo4-associated root coiling appears to be mechanistically different from the natural strong root curvature of the Arabidopsis ecotype Landsberg erecta. Gravistimulation reversibly overrides the aberrant thigmomorphogenesis of mlo4 seedlings. Mutants with dominant negative defects in α-tubulin modulate the extent and directionality of mlo4/mlo11-conditioned root coils, whereas mutants defective in polar auxin transport (axr4, aux1) or gravitropism (pgm1) completely suppress the mlo4 root curling phenotype. Our data implicate a joint contribution of calcium signalling, pH regulation, microtubular function, polar auxin transport and gravitropism in root thigmomorphogenesis.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Arabidopsis/fisiología , Genes de Plantas/genética , Morfogénesis/genética , Mutación/genética , Raíces de Plantas/crecimiento & desarrollo , Arabidopsis/efectos de los fármacos , Proteínas de Arabidopsis/metabolismo , Transporte Biológico/efectos de los fármacos , Calcio/farmacología , Oscuridad , Ecotipo , Ácido Egtácico/farmacología , Flavonoides/biosíntesis , Genes Supresores , Gravitación , Concentración de Iones de Hidrógeno , Ácidos Indolacéticos/metabolismo , Microtúbulos/efectos de los fármacos , Microtúbulos/metabolismo , Fenotipo , Raíces de Plantas/genética , TactoRESUMEN
Plant growth control has become a major focus due to economic reasons and results from a balance of cell proliferation in meristems and cell elongation that occurs during differentiation. Research on plant cell proliferation over the last two decades has revealed that the basic cell-cycle machinery is conserved between human and plants, although specificities exist. While many regulatory circuits control each step of the cell cycle, the ubiquitin proteasome system (UPS) appears in fungi and metazoans as a major player. In particular, the UPS promotes irreversible proteolysis of a set of regulatory proteins absolutely required for cell-cycle phase transitions. Not unexpectedly, work over the last decade has brought the UPS to the forefront of plant cell-cycle research. In this review, we will summarize our knowledge of the function of the UPS in the mitotic cycle and in endoreduplication, and also in meiosis in higher plants.
Asunto(s)
Ciclo Celular , Proteínas de Plantas/metabolismo , Desarrollo de la Planta , ProteolisisRESUMEN
Most cellular proteins involved in genome replication are conserved in all eukaryotic lineages including yeast, plants and animals. However, the mechanisms controlling their availability during the cell cycle are less well defined. Here we show that the Arabidopsis genome encodes for two ORC1 proteins highly similar in amino acid sequence and that have partially overlapping expression domains but with distinct functions. The ancestral ORC1b gene, present before the partial duplication of the Arabidopsis genome, has retained the canonical function in DNA replication. ORC1b is expressed in both proliferating and endoreplicating cells, accumulates during G1 and is rapidly degraded upon S-phase entry through the ubiquitin-proteasome pathway. In contrast, the duplicated ORC1a gene has acquired a specialized function in heterochromatin biology. ORC1a is required for efficient deposition of the heterochromatic H3K27me1 mark by the ATXR5/6 histone methyltransferases. The distinct roles of the two ORC1 proteins may be a feature common to other organisms with duplicated ORC1 genes and a major difference with animal cells.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Proteínas de Ciclo Celular , Secuencia de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Ciclo Celular/genética , Metiltransferasas , Complejo de Reconocimiento del Origen/genética , Fase S/genéticaRESUMEN
Powdery mildews are phytopathogens whose growth and reproduction are entirely dependent on living plant cells. The molecular basis of this life-style, obligate biotrophy, remains unknown. We present the genome analysis of barley powdery mildew, Blumeria graminis f.sp. hordei (Blumeria), as well as a comparison with the analysis of two powdery mildews pathogenic on dicotyledonous plants. These genomes display massive retrotransposon proliferation, genome-size expansion, and gene losses. The missing genes encode enzymes of primary and secondary metabolism, carbohydrate-active enzymes, and transporters, probably reflecting their redundancy in an exclusively biotrophic life-style. Among the 248 candidate effectors of pathogenesis identified in the Blumeria genome, very few (less than 10) define a core set conserved in all three mildews, suggesting that most effectors represent species-specific adaptations.
Asunto(s)
Ascomicetos/genética , Eliminación de Gen , Genes Fúngicos , Genoma Fúngico , Hordeum/microbiología , Enfermedades de las Plantas/microbiología , Adaptación Fisiológica , Ascomicetos/crecimiento & desarrollo , Ascomicetos/metabolismo , Ascomicetos/patogenicidad , Metabolismo de los Hidratos de Carbono , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Enzimas/genética , Enzimas/metabolismo , Evolución Molecular , Proteínas Fúngicas/química , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Interacciones Huésped-Patógeno/genética , Redes y Vías Metabólicas/genética , Anotación de Secuencia Molecular , Retroelementos , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
Conidiospores are the asexual propagation units of many plant-pathogenic fungi. In this article, we report an annotated proteome map of ungerminated conidiospores of the ascomycete barley powdery mildew pathogen, Blumeria graminis f.sp. hordei. Using a combination of two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, we have identified the proteins in 180 spots, which probably represent at least 123 distinct fungal gene products. Most of the identified proteins have a predicted function in carbohydrate, lipid or protein metabolism, indicating that the spore is equipped for the catabolism of storage compounds as well as for protein biosynthesis and folding on germination.
Asunto(s)
Ascomicetos/metabolismo , Proteómica , Esporas Fúngicas/metabolismo , Ascomicetos/ultraestructura , Proteínas Fúngicas/análisis , Péptidos/metabolismo , Enfermedades de las Plantas/microbiología , Isoformas de Proteínas/metabolismo , Proteoma/análisis , Esporas Fúngicas/ultraestructuraRESUMEN
Directional root expansion is governed by nutrient gradients, positive gravitropism and hydrotropism, negative phototropism and thigmotropism, as well as endogenous oscillations in the growth trajectory (circumnutation). Null mutations in phylogenetically related Arabidopsis thaliana genes MILDEW RESISTANCE LOCUS O 4 (MLO4) and MLO11, encoding heptahelical, plasma membrane-localized proteins predominantly expressed in the root tip, result in aberrant root thigmomorphogenesis. mlo4 and mlo11 mutant plants show anisotropic, chiral root expansion manifesting as tightly curled root patterns upon contact with solid surfaces. The defect in mlo4 and mlo11 mutants is nonadditive and dependent on light and nutrients. Genetic epistasis experiments demonstrate that the mutant phenotype is independently modulated by the Gbeta subunit of the heterotrimeric G-protein complex. Analysis of expressed chimeric MLO4/MLO2 proteins revealed that the C-terminal domain of MLO4 is necessary but not sufficient for MLO4 action in root thigmomorphogenesis. The expression of the auxin efflux carrier fusion, PIN1-green fluorescent protein, the pattern of auxin-induced gene expression, and acropetal as well as basipetal auxin transport are altered at the root tip of mlo4 mutant seedlings. Moreover, addition of auxin transport inhibitors or the loss of EIR1/AGR1/PIN2 function abolishes root curling of mlo4, mlo11, and wild-type seedlings. These results demonstrate that the exaggerated root curling phenotypes of the mlo4 and mlo11 mutants depend on auxin gradients and suggest that MLO4 and MLO11 cofunction as modulators of touch-induced root tropism.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Arabidopsis/crecimiento & desarrollo , Proteínas de la Membrana/fisiología , Raíces de Plantas/crecimiento & desarrollo , Apomorfina/análogos & derivados , Apomorfina/farmacología , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Transporte Biológico/efectos de los fármacos , Transporte Biológico/genética , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Ácidos Indolacéticos/metabolismo , Proteínas de la Membrana/genética , Proteínas de Transporte de Membrana/genética , Proteínas de Transporte de Membrana/fisiología , Microscopía Confocal , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/genética , Raíces de Plantas/metabolismo , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Estructura Terciaria de Proteína/genética , Estructura Terciaria de Proteína/fisiología , Plantones/efectos de los fármacos , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/metabolismoRESUMEN
The male gametophyte (or pollen) plays an obligatory role during sexual reproduction of higher plants. The extremely reduced complexity of this organ renders pollen a valuable experimental system for studying fundamental aspects of plant biology such as cell fate determination, cell-cell interactions, cell polarity, and tip-growth. Here, we present the first reference map of the mature pollen proteome of the dicotyledonous model plant species, Arabidopsis thaliana. Based on two-dimensional gel electrophoresis, matrix-assisted laser desorption/ionization time-of-flight, and electrospray quadrupole time-of-flight mass spectrometry, we reproducibly identified 121 different proteins in 145 individual spots. The presence, subcellular localization, and functional classification of the identified proteins are discussed in relation to the pollen transcriptome and the full protein complement encoded by the nuclear Arabidopsis genome.