RESUMO
Although life-history trade-offs are central to life-history evolution, their mechanistic basis is often unclear. Traditionally, trade-offs are understood in terms of competition for limited resources among traits within an organism, which could be mediated by signal transduction pathways at the level of cellular metabolism. Nevertheless, trade-offs are also thought to be produced as a consequence of the performance of one activity generating negative consequences for other traits, or the result of genes or pathways that simultaneously regulate two life-history traits in opposite directions (antagonistic pleiotropy), independent of resource allocation. Yet examples of genes with antagonistic effects on life-history traits are limited. This study provides direct evidence for a gene-RLS1, that is involved in increasing survival in nutrient-limiting environments at a cost to immediate reproduction in the single-celled photosynthetic alga, Chlamydomonas reinhardtii. Specifically, we show that RLS1 mutants are unable to properly suppress their reproduction in phosphate-deprived conditions. Although these mutants have an immediate reproductive advantage relative to the parental strain, their long-term survival is negatively affected. Our data suggest that RLS1 is a bona fide life-history trade-off gene that suppresses immediate reproduction and ensures survival by downregulating photosynthesis in limiting environments, as part of the general acclimation response to nutrient deprivation in photosynthetic organisms.
Assuntos
Reprodução , Fenótipo , Reprodução/fisiologiaRESUMO
Phosphate deprivation compromises plant productivity and modulates immunity. DAMP signalling by extracellular ATP (eATP) could be compromised under phosphate deprivation by the lowered production of cytosolic ATP and the need to salvage eATP as a nutritional phosphate source. Phosphate-starved roots of Arabidopsis can still sense eATP, indicating robustness in receptor function. However, the resultant cytosolic free Ca2+ signature is impaired, indicating modulation of downstream components. This perspective on DAMP signalling by extracellular ATP (eATP) addresses the salvage of eATP under phosphate deprivation and its promotion of immunity, how Ca2+ signals are generated and how the Ca2+ signalling pathway could be overcome to allow beneficial fungal root colonization to fulfill phosphate demands. Safe passage for an endophytic fungus allowing root colonization could be achieved by its down-regulation of the Ca2+ channels that act downstream of the eATP receptors and by also preventing ROS accumulation, thus further impairing DAMP signalling.
RESUMO
KEY MESSAGE: The role of the root cap in the plant response to phosphate deprivation has been scarcely investigated. Here we describe early structural, physiological and molecular changes prior to the determinate growth program of the primary roots under low Pi and unveil a critical function of the transcription factor SOMBRERO in low Pi sensing. Mineral nutrient distribution in the soil is uneven and roots efficiently adapt to improve uptake and assimilation of sparingly available resources. Phosphate (Pi) accumulates in the upper layers and thus short and branched root systems proliferate to better exploit organic and inorganic Pi patches. Here we report an early adaptive response of the Arabidopsis primary root that precedes the entrance of the meristem into the determinate developmental program that is a hallmark of the low Pi sensing mechanism. In wild-type seedlings transferred to low Pi medium, the quiescent center domain in primary root tips increases as an early response, as revealed by WOX5:GFP expression and this correlates with a thicker root tip with extra root cap cell layers. The halted primary root growth in WT seedlings could be reversed upon transfer to medium supplemented with 250 µM Pi. Mutant and gene expression analysis indicates that auxin signaling negatively affects the cellular re-specification at the root tip and enabled identification of the transcription factor SOMBRERO as a critical element that orchestrates both the formation of extra root cap layers and primary root growth under Pi scarcity. Moreover, we provide evidence that low Pi-induced root thickening or the loss-of-function of SOMBRERO is associated with expression of phosphate transporters at the root tip. Our data uncover a developmental window where the root tip senses deprivation of a critical macronutrient to improve adaptation and surveillance.
Assuntos
Proteínas de Arabidopsis/fisiologia , Ácidos Indolacéticos/metabolismo , Fosfatos/deficiência , Reguladores de Crescimento de Plantas/fisiologia , Coifa/crescimento & desenvolvimento , Fatores de Transcrição/fisiologia , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Arabidopsis/fisiologia , Regulação da Expressão Gênica de Plantas , Meristema/crescimento & desenvolvimento , Meristema/metabolismo , Meristema/fisiologia , Coifa/citologia , Coifa/metabolismo , Transdução de SinaisAssuntos
Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas , Nitratos/metabolismo , Nitrogênio/metabolismo , Nutrientes , Fosfatos , Raízes de Plantas/genética , Raízes de Plantas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Inorganic phosphate (Pi) is an essential macronutrient required for many fundamental processes in plants, including photosynthesis and respiration, as well as nucleic acid, protein, and membrane phospholipid synthesis. The huge use of Pi-containing fertilizers in agriculture demonstrates that the soluble Pi levels of most soils are suboptimal for crop growth. This review explores recent advances concerning the understanding of adaptive metabolic processes that plants have evolved to alleviate the negative impact of nutritional Pi deficiency. Plant Pi starvation responses arise from complex signaling pathways that integrate altered gene expression with post-transcriptional and post-translational mechanisms. The resultant remodeling of the transcriptome, proteome, and metabolome enhances the efficiency of root Pi acquisition from the soil, as well as the use of assimilated Pi throughout the plant. We emphasize how the up-regulation of high-affinity Pi transporters and intra- and extracellular Pi scavenging and recycling enzymes, organic acid anion efflux, membrane remodeling, and the remarkable flexibility of plant metabolism and bioenergetics contribute to the survival of Pi-deficient plants. This research field is enabling the development of a broad range of innovative and promising strategies for engineering phosphorus-efficient crops. Such cultivars are urgently needed to reduce inputs of unsustainable and non-renewable Pi fertilizers for maximum agronomic benefit and long-term global food security and ecosystem preservation.
Assuntos
Ecossistema , Fósforo , Adaptação Fisiológica , Fertilizantes , Fosfatos , Raízes de PlantasRESUMO
The benefit of chemotherapy as a constituent of transcatheter arterial chemoembolization (TACE) is still in debate. Recently we have developed arsenic trioxide nanoparticle prodrug (ATONP) as a new anticancer drug, but its systemic toxicity is a big issue. In this preclinical TACE study, ATONP emulsified in lipiodol behaved as drug-eluting bead manner. Sustained release of arsenic from ATONP within occluded tumor caused very low arsenic level in plasma, avoiding the "rushing out" effect as ATO did. Correspondingly, intratumoral arsenic accumulation and inorganic phosphate deprivation were simultaneously observed, and arsenic concentration was much higher as ATONP was transarterially administered than ATO, or intravenously injected. Tumor necrosis and apoptosis were remarkably more severe in ATONP group than ATO, but no significant hepatic and renal toxicity was perceived. In brief, ATONP alleviated arsenic toxicity and boosted the therapeutic effect of TACE via Pi-activated drug sustainable release.
Assuntos
Trióxido de Arsênio , Quimioembolização Terapêutica , Neoplasias Hepáticas Experimentais/terapia , Pró-Fármacos , Animais , Trióxido de Arsênio/farmacocinética , Trióxido de Arsênio/farmacologia , Preparações de Ação Retardada/farmacocinética , Preparações de Ação Retardada/farmacologia , Óleo Etiodado/química , Óleo Etiodado/farmacocinética , Óleo Etiodado/farmacologia , Neoplasias Hepáticas Experimentais/metabolismo , Neoplasias Hepáticas Experimentais/patologia , Pró-Fármacos/farmacocinética , Pró-Fármacos/farmacologia , CoelhosRESUMO
Chloroplasts contain high amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) and low levels of the anionic lipids sulfoquinovosyldiacylglycerol (SQDG), phosphatidylglycerol (PG), and glucuronosyldiacylglycerol (GlcADG). The mostly extraplastidial lipid phosphatidylcholine is found only in the outer envelope. Chloroplasts are the major site for fatty acid synthesis. In Arabidopsis, a certain proportion of glycerolipids is entirely synthesized in the chloroplast (prokaryotic lipids). Fatty acids are also exported to the endoplasmic reticulum and incorporated into lipids that are redistributed to the chloroplast (eukaryotic lipids). MGDG, DGDG, SQDG, and PG establish the thylakoid membranes and are integral constituents of the photosynthetic complexes. Phosphate deprivation induces phospholipid degradation accompanied by the increase in DGDG, SQDG, and GlcADG. During freezing and drought stress, envelope membranes are stabilized by the conversion of MGDG into oligogalactolipids. Senescence and chlorotic stress lead to lipid and chlorophyll degradation and the deposition of acyl and phytyl moieties as fatty acid phytyl esters.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Cloroplastos , Lipídeos , TilacoidesRESUMO
Low phosphate (Pi) availability is an important limiting factor affecting soybean production. However, the underlying molecular mechanisms responsible for low Pi stress response and tolerance remain largely unknown, especially for the early signaling events under low Pi stress. Here, a genome-wide transcriptomic analysis in soybean leaves treated with a short-term Pi-deprivation (24 h) was performed through high-throughput RNA sequencing (RNA-seq) technology. A total of 533 loci were found to be differentially expressed in response to Pi deprivation, including 36 mis-annotated loci and 32 novel loci. Among the differentially expressed genes (DEGs), 303 were induced and 230 were repressed by Pi deprivation. To validate the reliability of the RNA-seq data, 18 DEGs were randomly selected and analyzed by quantitative RT-PCR (reverse transcription polymerase chain reaction), which exhibited similar fold changes with RNA-seq. Enrichment analyses showed that 29 GO (Gene Ontology) terms and 8 KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways were significantly enriched in the up-regulated DEGs and 25 GO terms and 16 KEGG pathways were significantly enriched in the down-regulated DEGs. Some DEGs potentially involved in Pi sensing and signaling were up-regulated by short-term Pi deprivation, including five SPX-containing genes. Some DEGs possibly associated with water and nutrient uptake, hormonal and calcium signaling, protein phosphorylation and dephosphorylation and cell wall modification were affected at the early stage of Pi deprivation. The cis-elements of PHO (phosphatase) element, PHO-like element and P responsive element were present more frequently in promoter regions of up-regulated DEGs compared to that of randomly-selected genes in the soybean genome. Our transcriptomic data showed an intricate network containing transporters, transcription factors, kinases and phosphatases, hormone and calcium signaling components is involved in plant responses to early Pi deprivation.
Assuntos
Glycine max/genética , Fosfatos/deficiência , Folhas de Planta/metabolismo , Estresse Fisiológico , Transcriptoma , Regulação da Expressão Gênica de Plantas , Folhas de Planta/genética , Glycine max/metabolismoRESUMO
Photosynthetic organelles in plants and algae are characterized by the high abundance of glycolipids, including the galactolipids mono- and digalactosyldiacylglycerol (MGDG, DGDG) and the sulfolipid sulfoquinovosyldiacylglycerol (SQDG). Glycolipids are crucial to maintain an optimal efficiency of photosynthesis. During phosphate limitation, the amounts of DGDG and SQDG increase in the plastids of plants, and DGDG is exported to extraplastidial membranes to replace phospholipids. Algae often use betaine lipids as surrogate for phospholipids. Glucuronosyldiacylglycerol (GlcADG) is a further glycolipid that accumulates under phosphate deprived conditions. In contrast to plants, a number of eukaryotic algae contain very long chain polyunsaturated fatty acids of 20 or more carbon atoms in their glycolipids. The pathways and genes for galactolipid and sulfolipid synthesis are largely conserved between plants, Chlorophyta, Rhodophyta and algae with complex plastids derived from secondary or tertiary endosymbiosis. However, the relative contribution of the endoplasmic reticulum- and plastid-derived lipid pathways for glycolipid synthesis varies between plants and algae. The genes for glycolipid synthesis encode precursor proteins imported into the photosynthetic organelles. While most eukaryotic algae contain the plant-like galactolipid (MGD1, DGD1) and sulfolipid (SQD1, SQD2) synthases, the red alga Cyanidioschyzon harbors a cyanobacterium-type DGDG synthase (DgdA), and the amoeba Paulinella, derived from a more recent endosymbiosis event, contains cyanobacterium-type enzymes for MGDG and DGDG synthesis (MgdA, MgdE, DgdA).
Assuntos
Galactolipídeos/metabolismo , Glicolipídeos/metabolismo , Microalgas/metabolismo , Plantas/metabolismo , Galactolipídeos/química , Glicolipídeos/química , Estrutura MolecularRESUMO
Growing agricultural demands in the face of impending inorganic phosphate (Pi) shortages underscore a need for a better understanding of plant development under conditions of Pi deprivation. Pi is an essential nutrient that is a major component of fertilizer. Plants have evolved strategies to improve the acquisition of this nutrient by altering root development under shortage conditions. We show that signaling peptides thought to act redundantly in Arabidopsis thaliana development have distinct functions in response to Pi deprivation. Using microscopy and confocal imaging, roots were analyzed for growth rate and cellular composition. Using expression microarrays, genes influencing development in response to phosphate deprivation were identified. ROOT GROWTH FACTOR1 (RGF1) and RGF2 influenced different aspects of root development under conditions of Pi deprivation. We found that RGF2 influenced the longitudinal growth rate in the primary root in response to Pi deprivation, whereas RGF1 affected circumferential cell number in the root meristem. These data suggest that the mechanisms controlling adaptive development can depend on disparate functions of genes thought to act redundantly, thus elucidating new functions for important developmental regulators.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Peptídeos/metabolismo , Fosfatos/deficiência , Raízes de Plantas/crescimento & desenvolvimento , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Contagem de Células , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas , Meristema/anatomia & histologia , Meristema/efeitos dos fármacos , Meristema/genética , Proteínas Mutantes/metabolismo , Peptídeos/genética , Fosfatos/farmacologia , Epiderme Vegetal/efeitos dos fármacos , Epiderme Vegetal/genética , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genéticaRESUMO
Induction and secretion of acid phosphatases (APases) is thought to be an adaptive mechanism that helps plants survive and grow under phosphate (Pi) deprivation. In Arabidopsis, there are 29 purple acid phosphatase (AtPAP) genes. To systematically investigate the roles of different AtPAPs, we first identified knockout or knock-down T-DNA lines for all 29 AtPAP genes. Using these atpap mutants combined with in-gel and quantitative APase enzyme assays, we demonstrated that AtPAP12 and AtPAP26 are two major intracellular and secreted APases in Arabidopsis while AtPAP10 is mainly a secreted APase. On Pi-deficient (P-) medium or P- medium supplemented with the organophosphates ADP and fructose-6-phosphate (Fru-6-P), growth of atpap10 was significantly reduced whereas growth of atpap12 was only moderately reduced, and growth of atpap26 was nearly equal to that of the wild type (WT). Overexpression of the AtPAP12 or AtPAP26 gene, however, caused plants to grow better on P- or P- medium supplemented with ADP or Fru-6-P. Interestingly, Pi levels are essentially the same for the WT and overexpressing lines, although these two types of plants have significantly different growth phenotypes. These results suggest that the APases may have other roles besides enhancing internal Pi recycling or releasing Pi from external organophosphates for plant uptake.