The NAC transcription factor ANAC017 regulates aluminum tolerance by regulating the cell wall-modifying genes

Aluminum (Al) toxicity is one of the key factors limiting crop production in acid soils; however, little is known about its transcriptional regulation in plants. In this study, we characterized the role of a NAM, ATAF1/2, and cup-shaped cotyledon 2 (NAC) transcription factors (TFs), ANAC017, in the regulation of Al tolerance in Arabidopsis (Arabidopsis thaliana). ANAC017 was localized in the nucleus and exhibited constitutive expression in the root, stem, leaf, flower, and silique, although its expression and protein accumulation were repressed by Al stress. Loss of function of ANAC017 enhanced Al tolerance when compared with wild-type Col-0 and was accompanied by lower root and root cell wall Al content. Furthermore, both hemicellulose and xyloglucan content decreased in the anac017 mutants, indicating the possible interaction between ANAC017 and xyloglucan endotransglucosylase/hydrolase (XTH). Interestingly, the expression of XTH31, which is responsible for xyloglucan modification, was downregulated in the anac017 mutants regardless of Al supply, supporting the possible interaction between ANAC017 and XTH31. Yeast one-hybrid, dual-luciferase reporter assay, and chromatin immunoprecipitation-quantitative PCR analysis revealed that ANAC017 positively regulated the expression of XTH31 through directly binding to the XTH31 promoter region, and overexpression of XTH31 in the anac017 mutant background rescued its Al-tolerance phenotype. In conclusion, we identified that the tTF ANAC017 acts upstream of XTH31 to regulate Al tolerance in Arabidopsis.

[Exploring and bioinformatics analysis of differentially expressed genes in bronchial asthma]

Objective: To screen core differentially expressed genes of bronchial asthma and conduct bioinformatics analysis. Methods: Macrophage microarray data GSE22528 from asthma patients were downloaded from gene expression database (GEO). The dataset included transcriptome information from 10 human alveolar lavage fluid samples, and five of them were from allergic asthmatic subjects and five from control subjects. Differential expression genes (DEGs) were screened by R 4.0.4 software. Gene ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed to select DEGs using DAVID 6.8 database. Protein interaction network (PPI) was constructed from DEGs encoded proteins using STRING online database. Cytoscape software was used to construct core modules and determine core DEGs. Results: Alveolar lavage fluid samples were all collected from Caucasian Canadians, with age range as (20, 37) and (18, 36) years, respectively, including 3 males for each group. In asthmatic patients, 449 genes were up-regulated and 47 down-regulated. GO analysis showed that the up-regulated genes in asthmatic patients were mainly involved in biological processes such as response to folded proteins, and the molecular function was focused on binding of folded proteins and growth factors. Down-regulated genes were mainly involved in biological processes such as histone deacetylation and ubiquitin-mediated protein degradation, and their molecular functions focused on histone deacetylation activity. KEGG pathway enrichment analysis showed that pathways were mainly enriched by up-regulation genes, involving Hippo signaling pathway, hypertrophic cardiomyopathy, estrogen signaling pathway, arrhythmogenic right ventricular cardiomyopathy, basal cell carcinoma, neuro-activated receptor ligand interaction, dilated cardiomyopathy and adhesion and connection signaling pathways. Two core modules were obtained by PPI analysis, and 14 core DEGs were screened out. They were pro-melanin concentrating hormone (PMCH), prepronociceptin (PNOC), Sphingosinol-1-phosphate receptor 2 (S1PR2), Sphingosinol-1-phosphate receptor 5 (S1PR5), CC-type chemokine ligand 21 (CCL21), Kelch-like protein 25 (KLHL25), ubiquitin binding enzyme E2V2 (UBE2V2), F-box protein 17 (FBXO17), taste receptor type 2 member 3 (TAS2R3), somatostatin receptor 2 (SSTR2), metabolic glutamate receptor 2 (GRM2), Lister E3 ubiquitin protein ligase 1 (LTN1), LIM domain specific protein 7 (LMO7) and ring finger protein 19A gene(RNF19A), in which LTN1 and UBE2V2 were down-regulated and the rest were up-regulated. Conclusion: DEGs was found in macrophages of asthmatic and control individuals. PMCH, PNOC, S1PR2, S1PR5 and CCL21 might be the core genes in the pathological process of asthma.

[Human bone marrow mesenchymal stem cells improve steroid resistance of human airway epithelial BEAS-2B cells in vitro]

Objective: To explore the effect of human bone marrow mesenchymal stem cells(MSC) on the steroid resistance of human airway epithelial cells. Methods: Ovalbumin (OVA)/lipopolysaccharide (LPS) were used to construct steroid resistant BEAS-2B cells, which were then co-cultured with MSC. Groups were set as follows: blank group, model group, Glucocorticoid group, MSC group, MSC+Glucocorticoid group (MSC+bud group). The expression of interleukin (IL)-8 in the cell supernatant was detected by enzyme-linked immunosorbent assay (ELISA); the expression of reactive oxygen species (ROS) in the cells was detected by flow cytometry; the expression of glucocorticoid receptor α (GRα) and histone deacetylase 2 (HDAC2) protein in the cell was detected by Western blotting; and the expression of GRα and HDAC2 mRNA was detected by reverse transcription-polymerase chain reaction (RTPCR). Results: The expression level of IL-8 in the MSC group was significantly lower than that in the Glucocorticoid group (31.7±0.7 vs. 49.8±3.6, P<0.01). The expression of ROS in the MSC group was significantly lower than that in the Glucocorticoid group (2754±154 vs.4624±228, P<0.05). The expression level of HDAC2 mRNA in the MSC group was significantly higher than that in the Glucocorticoid group(1.749±0.005 vs. 1.283±0.098, P<0.05). The expression level of GRα mRNA in the MSC group was significantly higher than that in the Glucocorticoid group (1.623±0.079 vs.1.047±0.220, P<0.01). The expression of HDAC2 protein in the MSC group was significantly higher than that in the Glucocorticoid group (1.067±0.100 vs. 0.620±0.083, P<0.01). The expression of GRα protein in the MSC group was significantly higher than that in the Glucocorticoid group (0.834±0.053 vs. 0.579±0.017, P<0.01). ROS was positively correlated with the IL-8 expression (r=0.796, P<0.01) and negatively correlated with the HDAC2 and GRα mRNA expression (r=-0.893 3, P<0.01; r=0.931 4, P<0.01, respectively), as well as the HDAC2 and GRα Protein expression (r=-0.929 5, P<0.01;r=-0.864 3, P<0.01, respectively). Conclusions: Human MSC can improve steroid resistance of airway epithelial cells in an exocrine manner. The mechanism may be related to the down-regulation of ROS and up-regulation of HDAC2, which lead to GRα overexpression. In addition, MSC may improve the steroid resistance by reducing the expression of IL-8.

PARVUS affects aluminium sensitivity by modulating the structure of glucuronoxylan in Arabidopsis thaliana

Glucuronoxylan (GX), an important component of hemicellulose in the cell wall, appears to affect aluminium (Al) sensitivity in plants. To investigate the role of GX in cell-wall-localized xylan, we examined the Arabidopsis thaliana parvus mutant in detail. This mutant lacks α-D-glucuronic acid (GlcA) side chains in GX and has greater resistance to Al stress than wild-type (WT) plants. The parvus mutant accumulated lower levels of Al in its roots and cell walls than WT despite having cell wall pectin content and pectin methylesterase (PME) activity similar to those of WT. Our results suggest that the altered properties of hemicellulose in the mutant contribute to its decreased Al accumulation. Although we observed almost no differences in hemicellulose content between parvus and WT under control conditions, less Al was retained in parvus hemicellulose than in WT. This observation is consistent with the finding that GlcA substitutions in WT GX, but not mutant GX, were increased under Al stress. Taken together, these results suggest that the modulation of GlcA levels in GX affects Al resistance by influencing the Al binding capacity of the root cell wall in Arabidopsis.

Pectin enhances rice (Oryza sativa) root phosphorus remobilization

Plants growing in phosphorus (P)-deficient conditions can either increase their exploration of the environment (hence increasing P uptake) or can solubilize and reutilize P from established tissue sources. However, it is currently unclear if P stored in root cell wall can be reutilized. The present study shows that culture of the rice cultivars 'Nipponbare' (Nip) and 'Kasalath' (Kas) in P-deficient conditions results in progressive reductions in root soluble inorganic phosphate (Pi). However, Nip consistently maintains a higher level of soluble Pi and lower relative cell wall P content than does Kas, indicating that more cell wall P is released in Nip than in Kas. P-deficient Nip has a greater pectin and hemicellulose 1 (HC1) content than does P-deficient Kas, consistent with the significant positive relationship between pectin and root-soluble Pi levels amongst multiple rice cultivars. These observations suggest that increased soluble Pi might result from increased pectin content during P starvation. In vitro experiments showed that pectin releases Pi from insoluble FePO4. Furthermore, an Arabidopsis thaliana mutant with reduced pectin levels (qua1-2), has less root soluble Pi and is more sensitive to P deficiency than the wild type (WT) Col-0, whereas NaCl-treated WT plants exhibit both an increased root pectin content and an elevated soluble Pi content during P-starvation. These observations indicate that pectin can facilitate the remobilization of P deposited in the cell wall. This is a previously unknown mechanism for the reutilization of P in P-starved plants.

TRICHOME BIREFRINGENCE-LIKE27 affects aluminum sensitivity by modulating the O-acetylation of xyloglucan and aluminum-binding capacity in Arabidopsis

Xyloglucan (XyG) has been reported to contribute to the aluminum (Al)-binding capacity of the cell wall in Arabidopsis (Arabidopsis thaliana). However, the influence of O-acetylation of XyG, accomplished by the putative O-acetyltransferase TRICHOME BIREFRINGENCE-LIKE27 (TBL27 [AXY4]), on its Al-binding capacity is not known. In this study, we found that the two corresponding TBL27 mutants, axy4-1 and axy4-3, were more Al sensitive than wild-type Columbia-0 plants. TBL27 was expressed in roots as well as in leaves, stems, flowers, and siliques. Upon Al treatment, even within 30 min, TBL27 transcript accumulation was strongly down-regulated. The mutants axy4-1 and axy4-3 accumulated significantly more Al in the root and wall, which could not be correlated with pectin content or pectin methylesterase activity, as no difference in the mutants was observed compared with the wild type when exposed to Al stress. The increased Al accumulation in the wall of the mutants was found to be in the hemicellulose fraction. While the total sugar content of the hemicellulose fraction did not change, the O-acetylation level of XyG was reduced by Al treatment. Taken together, we conclude that modulation of the O-acetylation level of XyG influences the Al sensitivity in Arabidopsis by affecting the Al-binding capacity in the hemicellulose.

Xyloglucan Endotransglucosylase-Hydrolase17 Interacts with Xyloglucan Endotransglucosylase-Hydrolase31 to Confer Xyloglucan Endotransglucosylase Action and Affect Aluminum Sensitivity in Arabidopsis

Previously, we reported that although the Arabidopsis (Arabidopsis thaliana) Xyloglucan Endotransglucosylase-Hydrolase31 (XTH31) has predominately xyloglucan endohydrolase activity in vitro, loss of XTH31 results in remarkably reduced in vivo xyloglucan endotransglucosylase (XET) action and enhanced Al resistance. Here, we report that XTH17, predicted to have XET activity, binds XTH31 in yeast (Saccharomyces cerevisiae) two-hybrid and coimmunoprecipitations assays and that this interaction may be required for XTH17 XET activity in planta. XTH17 and XTH31 may be colocalized in plant cells because tagged XTH17 fusion proteins, like XTH31 fusion proteins, appear to target to the plasma membrane. XTH17 expression, like that of XTH31, was substantially reduced in the presence of aluminum (Al), even at concentrations as low as 10 µm for 24 h or 25 µm for just 30 min. Agrobacterium tumefaciens-mediated transfer DNA insertion mutant of XTH17, xth17, showed low XET action and had moderately shorter roots than the wild type but was more Al resistant than the wild type. Similar to xth31, xth17 had low hemicellulose content and retained less Al in the cell wall. These data suggest a model whereby XTH17 and XTH31 may exist as a dimer at the plasma membrane to confer in vivo XET action, which modulates cell wall Al-binding capacity and thereby affects Al sensitivity in Arabidopsis.

Preparation and mechanical property of poly(ε-caprolactone)-matrix composites containing nano-apatite fillers modified by silane coupling agents

This study aims to improve the tensile strength and elastic modulus of nano-apatite/poly(ε-caprolactone) composites by silane-modification of the nano-apatite fillers. Three silane coupling agents were used to modify the surfaces of nano-apatite particles and composites of silanized apatite and PCL were prepared by a technique incorporating solvent dispersion, melting-blend and hot-pressing. The results showed that the silane coupling agents successfully modified the surfaces of nano-apatite fillers, and the crystallization temperatures of the silanized apatite/PCL composites were the higher than that of the non-silanized control material, although the melting temperature of the composites remained almost unaffected by silanization. The ultimate tensile strength and elastic modulus of the silanized composites reached 22.60 MPa and 1.76 GPa, as a result of the improved interfacial bonding and uniform dispersion of nano-apatite fillers. This study shows that the processing technique and silanization of nano-apatite particles can effectively improve the tensile strength and elastic modulus of nano-apatite/PCL composites.