RESUMO
Phosphorus (as phosphate, Pi) and iron (Fe) are critical nutrients in plants that are often poorly available in the soil and can be microbially affected. This work aimed to evaluate how plant-rhizobacteria interaction changes due to different Pi or Fe nutritional scenarios and to study the underlying molecular mechanisms of the microbial modulation of these nutrients in plants. Thus, three proteobacteria (Paraburkholderia phytofirmans PsJN, Azospirillum brasilense Sp7, and Pseudomonas putida KT2440) were used to inoculate Arabidopsis seeds. Additionally, the seeds were exposed to a nutritional factor with the following levels for each nutrient: sufficient (control) or low concentrations of a highly soluble source or sufficient concentrations of a low solubility source. Then, the effects of the combinatorial factors were assessed in plant growth, nutrition, and genetic regulation. Interestingly, some bacterial effects in plants depended on the nutrient source (e.g., increased aerial zones induced by the strains), and others (e.g., decreased primary roots induced by Sp7 or KT2440) occurred regardless of the nutritional treatment. In the short-term, PsJN had detrimental effects on plant growth in the presence of the low-solubility Fe compound, but this was not observed in later stages of plant development. A thorough regulation of the phosphorus content was detected in plants independent of the nutritional treatment. Nevertheless, inoculation with KT2440 increased P content by 29% Pi-deficiency exposed plants. Conversely, the inoculation tended to decrease the Fe content in plants, suggesting a competition for this nutrient in the rhizosphere. The P-source also affected the effects of the PsJN strain in a double mutant of the phosphate starvation response (PSR). Furthermore, depending on the nutrient source, PsJN and Sp7 strains differentially regulated PSR and IAA- associated genes, indicating a role of these pathways in the observed differential phenotypical responses. In the case of iron, PsJN and SP7 regulated iron uptake-related genes regardless of the iron source, which may explain the lower Fe content in inoculated plants. Overall, the plant responses to these proteobacteria were not only influenced by the nutrient concentrations but also by their availabilities, the elapsed time of the interaction, and the specific identities of the beneficial bacteria. Graphical AbstractThe effects of the different nutritional and inoculation treatments are indicated for plant growth parameters (A), gene regulation (B) and phosphorus and iron content (C). Figures created with BioRender.com with an academic license.
RESUMO
Abortion of fertilized ovaries at the tip of the ear can generate significant yield losses in maize crops. To investigate the mechanisms involved in this process, 2 maize hybrids were grown in field crops at 2 sowing densities and under 3 irrigation regimes (well-watered control, drought before pollination, and drought during pollination), in all possible combinations. Samples of ear tips were taken 2-6 days after synchronous hand pollination and used for the analysis of gene expression and sugars. Glucose and fructose levels increased in kernels with high abortion risk. Several FASCICLIN-LIKE ARABINOGALACTAN PROTEIN (FLA) genes showed negative correlation with abortion. The expression of ZmFLA7 responded to drought only at the tip of the ear. The abundance of arabinogalactan protein (AGP) glycan epitopes decreased with drought and pharmacological treatments that reduce AGP activity enhanced the abortion of fertilized ovaries. Drought also reduced the expression of AthFLA9 in the siliques of Arabidopsis thaliana. Gain- and loss-of-function mutants of Arabidopsis showed a negative correlation between AthFLA9 and seed abortion. On the basis of gene expression patterns, pharmacological, and genetic evidence, we propose that stress-induced reductions in the expression of selected FLA genes enhance abortion of fertilized ovaries in maize and Arabidopsis.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Mucoproteínas/genética , Proteínas de Plantas/genética , Sementes/fisiologia , Zea mays/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/metabolismo , Quimera , Secas , Glucosídeos/farmacologia , Mucoproteínas/metabolismo , Óvulo Vegetal/genética , Óvulo Vegetal/fisiologia , Floroglucinol/análogos & derivados , Floroglucinol/farmacologia , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Polinização , Sementes/genética , Zea mays/efeitos dos fármacos , Zea mays/fisiologiaRESUMO
Root hair polar growth is endogenously controlled by auxin and sustained by oscillating levels of reactive oxygen species (ROS). These cells extend several hundred-fold their original size toward signals important for plant survival. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown. Here we show that ROS production is controlled by the transcription factor RSL4, which in turn is transcriptionally regulated by auxin through several auxin response factors (ARFs). In this manner, auxin controls ROS-mediated polar growth by activating RSL4, which then up-regulates the expression of genes encoding NADPH oxidases (also known as RESPIRATORY BURST OXIDASE HOMOLOG proteins) and class III peroxidases, which catalyze ROS production. Chemical or genetic interference with ROS balance or peroxidase activity affects root hair final cell size. Overall, our findings establish a molecular link between auxin and ROS-mediated polar root hair growth.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas de Arabidopsis/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Regulação da Expressão Gênica de Plantas , NADPH Oxidases/metabolismo , Peroxidases/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Bryopsis sp. from a restricted area of the rocky shore of Mar del Plata (Argentina) on the Atlantic coast was identified as Bryopsis plumosa (Hudson) C. Agardh (Bryopsidales, Chlorophyta) based on morphological characters and rbcL and tufA DNA barcodes. To analyze the cell wall polysaccharides of this seaweed, the major room temperature (B1) and 90°C (X1) water extracts were studied. By linkage analysis and NMR spectroscopy, the structure of a sulfated galactan was determined, and putative sulfated rhamnan structures and furanosidic nonsulfated arabinan structures were also found. By anion exchange chromatography of X1, a fraction (F4), comprising a sulfated galactan as major structure was isolated. Structural analysis showed a linear backbone constituted of 3-linked ß-d-galactose units, partially sulfated on C-6 and partially substituted with pyruvic acid forming an acetal linked to O-4 and O-6. This galactan has common structural features with those of green seaweeds of the genus Codium (Bryopsidales, Chlorophyta), but some important differences were also found. This is the first report about the structure of the water-soluble polysaccharides biosynthesized by seaweeds of the genus Bryopsis. These sulfated galactans and rhamnans were in situ localized mostly in two layers, one close to the plasma membrane and the other close to the apoplast, leaving a middle amorphous, unstained cell wall zone. In addition, fibrillar polysaccharides, comprising (1â3)-ß-d-xylans and cellulose, were obtained by treatment of the residue from the water extractions with an LiCl/DMSO solution at high temperature. These polymers were also localized in a bilayer arrangement.
RESUMO
ß-(1â4)-d-Mannans constitute the major component of the cell wall of seaweeds of the genus Codium and replace cellulose as the major fibrillar component. They were found as major constituents of the hot water extracts of green seaweed Codium vermilara. By anion exchange chromatography of the first hot water extract, a pure sulfated mannan with a molar ratio carbohydrates:sulfate of 2.7:1 was isolated. The sulfate groups are linked to C-2 of 23% of the mannose units, while most of these units are not substituted. This degree of sulfation would explain the higher solubility of the polymer, compared to that of the non-sulfated fibrillar mannan. Taking into account that the fibrillar polysaccharides form two external layers in the cell wall, while the sulfated polymers are forming an amorphous central layer, it is postulated that these sulfated mannans could act as an interphase region between the neutral and acidic layers.
RESUMO
Snakin-1 (SN1) is an antimicrobial cysteine-rich peptide isolated from potato (Solanum tuberosum) that was classified as a member of the Snakin/Gibberellic Acid Stimulated in Arabidopsis protein family. In this work, a transgenic approach was used to study the role of SN1 in planta. Even when overexpressing SN1, potato lines did not show remarkable morphological differences from the wild type; SN1 silencing resulted in reduced height, which was accompanied by an overall reduction in leaf size and severe alterations of leaf shape. Analysis of the adaxial epidermis of mature leaves revealed that silenced lines had 70% to 90% increases in mean cell size with respect to wild-type leaves. Consequently, the number of epidermal cells was significantly reduced in these lines. Confocal microscopy analysis after agroinfiltration of Nicotiana benthamiana leaves showed that SN1-green fluorescent protein fusion protein was localized in plasma membrane, and bimolecular fluorescence complementation assays revealed that SN1 self-interacted in vivo. We further focused our study on leaf metabolism by applying a combination of gas chromatography coupled to mass spectrometry, Fourier transform infrared spectroscopy, and spectrophotometric techniques. These targeted analyses allowed a detailed examination of the changes occurring in 46 intermediate compounds from primary metabolic pathways and in seven cell wall constituents. We demonstrated that SN1 silencing affects cell division, leaf primary metabolism, and cell wall composition in potato plants, suggesting that SN1 has additional roles in growth and development beyond its previously assigned role in plant defense.
Assuntos
Parede Celular/química , Proteínas de Plantas/genética , Solanum tuberosum/genética , Solanum tuberosum/metabolismo , Divisão Celular , Membrana Celular/metabolismo , Parede Celular/genética , Parede Celular/metabolismo , Cromatografia Gasosa-Espectrometria de Massas , Regulação da Expressão Gênica de Plantas , Inativação Gênica , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Dados de Sequência Molecular , Epiderme Vegetal/citologia , Epiderme Vegetal/genética , Folhas de Planta/genética , Folhas de Planta/fisiologia , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Solanaceae/genética , Solanum tuberosum/citologia , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Cell wall chemistry in the coencocytic green seaweed Codium vermilara (Olivi) Delle Chiaje (Bryopsidales, Chlorophyta) is well understood. These cell walls are composed of major amounts of neutral ß-(1â4)-D-mannans (Mn), sulfated polysaccharides (SPs), which include pyranosic arabinan sulfates (ArpS), pyruvylated galactan sulfates (pGaS), and mannan sulfates (MnS); also minor amounts of O-glycoproteins are present. In this study, cell wall samples of C. vermilara were investigated with regard to their monosaccharide composition and infrared spectra (using Fourier transform infrared spectroscopy coupled to principal component [FTIR-PC] analysis). Samples from three different populations of C. vermilara from the Argentine coast showed: (i) an important variation in the relative arabinan content, which increases from north to south, and (ii) a measurable degree of cell wall variability in the sulfate distribution between the different sulfated polysaccharides, independent of the amount of each polysaccharide present and of total sulfate content. When cell wall composition was analyzed over three consecutive years in a single geographic location, the quantity of Mn and overall sulfate content on SPs remained constant, whereas the pGaS:ArpS molar ratio changed over the time. Besides, similar cell wall composition was found between actively growing and resting zones of the thallus, suggesting that cell wall composition is independent of growth stage and development. Overall, these results suggest that C. vermilara has developed a mechanism to adjust the total level of cell wall sulfation by modulating the ArpS:pGaS:MnS molar ratio and also by adjusting the sulfation level in each type of polymer, whereas nonsulfated Mn, as the main structural polysaccharide, did not change over the time or growing stage.
RESUMO
Codium fragile and Codium vermilara biosynthesize water-soluble sulfated arabinans and galactans (and/or sulfated arabinogalactans), alpha(1-->4)-D-glucans and beta(1-->4)-D-mannans. The former polysaccharides are composed by 3-linked beta-D-galactopyranose and beta-L-arabinopyranose residues, they are highly sulfated and substituted with pyruvic acid ketals. For both seaweeds, they have the same main structural units, but in different percentages. All the room-temperature water extracts from both seaweeds showed a dual haemostatic effect: they prevented coagulation, but they induced platelet aggregation. Anticoagulant activity and platelet aggregation were higher in the samples with polysaccharides richer in sulfate, mainly in those from C. vermilara, which have a higher degree of sulfation and arabinose content.