The influence of β-glucan on the growth and cell wall architecture of Aspergillus spp

β-1,3-glucan is a major component of fungal cell walls with various biological activities, including effects on the production of inflammatory mediators in vivo and in vitro. However, few reports have examined its influence on the fungal cell itself. In this study, the influences of β-1,3-glucan on the growth and cell wall structure of fungi was examined. Aspergillus fumigatus was cultured with a synthetic medium, C-limiting medium, in the presence or absence of β-1,3-glucan. Hyphal growth was promoted in liquid and solid-cultures by adding β-1,3-glucan. Glucose and dextran did not induce growth. The influence on cell wall structure of the β-glucan-added cultures was examined by enzymolysis and NMR spectroscopy and the amount of β-1,3-glucan found to be changed. β-1,3-glucan has been widely detected in the environment. In this study, it was demonstrated that β-1,3-glucan causes promotion of the growth, and a change in the cell wall architecture, of Aspergillus. Unregulated distribution of β-1,3-glucan would be strongly related to the incidence of infectious diseases and allergy caused by Aspergillus spp.     

Development and application of a system for seminolipid metabolism using mouse seminiferous tubules

A convenient tool for studying metabolism of seminolipid in testis was developed by using mouse isolated seminiferous tubules prepared by collagenase treatment. Because more than 99% of [³⁵S]sulfate-incorporation was distributed in seminolipid, its metabolism in seminiferous tubules can be analyzed without disturbance of the other sulfolipids in this assay system. Furthermore, the contents of seminolipid and its precursor, galactosylalkylacylglycerol, which were determined by liquid chromatography-electrospray ionization mass spectrometry, did not change within a few hours, indicating that the incorporations of [³⁵S]sulfate into seminolipid solely reflects the turnover rate of this sulfolipid. As an initial application of this system, we characterized heat-susceptibility of the seminolipid turnover rate in mouse seminiferous tubules. Severe heating (44°C for 10 min) of the isolated seminiferous tubules suppressed the ³⁵S-incorporation into seminolipid to 47% of heating at scrotal temperature (32°C for 70 min). In contrast, pretreatment of the testis in vivo under the same condition (44°C for 10 min) did not decrease the seminolipid turnover rate in the isolated seminiferous tubules. In addition, the activity of galactocerebroside sulfotransferase decreased in the temperature-dependent manner in seminiferous tubules as well as crude tubular homogenates, where the activity is significantly more stable in the former than the latter. The newly developed system could provide useful basic data for further analyses of seminolipid metabolism in the testis.     

Periostin Associates with Notch1 Precursor to Maintain Notch1 Expression under a Stress Condition in Mouse Cells

Background

Matricellular proteins, including periostin, modulate cell-matrix interactions and cell functions by acting outside of cells.

Methods and Findings

In this study, however, we reported that periostin physically associates with the Notch1 precursor at its EGF repeats in the inside of cells. Moreover, by using the periodontal ligament of molar from periostin-deficient adult mice (Pn−/− molar PDL), which is a constitutively mechanically stressed tissue, we found that periostin maintained the site-1 cleaved 120-kDa transmembrane domain of Notch1 (N1™) level without regulating Notch1 mRNA expression. N1™ maintenance in vitro was also observed under such a stress condition as heat and H₂O₂ treatment in periostin overexpressed cells. Furthermore, we found that the expression of a downstream effector of Notch signaling, Bcl-xL was decreased in the Pn−/− molar PDL, and in the molar movement, cell death was enhanced in the pressure side of Pn−/− molar PDL.

Conclusion

These results suggest the possibility that periostin inhibits cell death through up-regulation of Bcl-xL expression by maintaining the Notch1 protein level under the stress condition, which is caused by its physical association with the Notch1 precursor.     

Effect of abscisic acid on symbiotic nitrogen fixation activity in the root nodules of Lotus japonicus

The phytohormone abscisic acid (ABA) is known to be a negative regulator of legume root nodule formation. By screening Lotus japonicus seedlings for survival on an agar medium containing 70 µM ABA, we obtained mutants that not only showed increased root nodule number, but also enhanced nitrogen fixation. The mutant was designated enf1 (enhanced nitrogen fixation 1) and was confirmed to be monogenic and incompletely dominant.In long-term growth experiments with M. loti, although some yield parameters were the same for both enf1 and wild-type plants, both the dry weight and N content of 100 seeds and entire enf1 plants were significantly larger compared than those traits in wild-type seeds and plants. The augmentation of the weight and N content of the enf1 plants most likely reflects the increased N supplied by the additional enf1 nodules and the concomitant increase in N fixation activity.We determined that the endogenous ABA concentration and the sensitivity to ABA of enf1 were lower than that of wild-type seedlings. When wild-type plants were treated with abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase (NCED), which results in reduced ABA content, the N fixation activity of abamine-treated plants was elevated to the same levels as enf1. We also determined that production of nitric oxide (NO) in enf1 nodules was decreased. We conclude that endogenous ABA concentration not only regulates nodulation, but also nitrogen fixation activity by decreasing NO production in nodules.Key words: Lotus japonicus, symbiotic nitrogen fixation, nitric oxide, ABA, root nodulePhytohormones are known to be important for regulating the number of nodules established on the root of legumes.¹ For example, ethylene is a well-known negative regulator of nodulation, influencing the earliest stages from the perception of Nod factor to the growth of infection threads.^2–4 In contrast, cytokinin is a positive regulator of nodulation. The cytokinin insensitive mutant hit1 (loss-of-function) of Lotus japonicus and the snf2 (gain-of-function) mutants of Medicago truncatula provide genetic evidence demonstrating that cytokinin plays a critical role in the activation of nodule primordia.^5–7Abscisic acid (ABA), added at concentrations that do not affect plant growth, also negatively regulates nodulation in some legumes.^8–11 Recently, Medicago truncatula overexpressing abi1-1, a gene that encodes a mutated protein phosphatase of the type IIC class derived from Arabidopsis and that suppresses the ABA signaling pathway,^12,13 was shown to exhibit ABA insensitivity as well as a hypernodulating phenotype.¹⁴In this study, we isolated a Lotus japonicus (Miyakojima MG20) mutant that showed an increased root nodule phenotype and a lowered sensitivity to ABA, and proceeded to carry out its characterization. This mutant, named enf1 (enhanced nitrogen fixation 1) exhibit enhanced symbiotic N fixation activity. Most legume N fixation activity mutants, such as ign1, sen1 and sst1, are Fix-.^15–17At first, to obtain ABA-insensitive or low-sensitive mutants of Lotus japonicus, we treated Miyakojima MG20 with EMS to induce base substitutions randomly in the genome. M3 seeds were sown on an agar-solidified medium containing 70 µM ABA, a concentration that inhibits the germination of wild-type MG20 seeds. M4 plants obtained by the screening were inoculated with rhizobia (Mesorhizobium loti MAFF303099), and the number of nodules per plant was counted 35 days after inoculation (DAI). Plant No. 12 not only formed more root nodules than did the wild-type MG20 plants, but surprisingly it also exhibited increased nitrogen fixation activity per plant. Both mutant phenotypes were stably inherited in the M4 and M5 generation. Back-crossing mutant No. 12 to wild-type MG20 yielded 153 F2 progeny from which a line that showed the highest N fixation activity and more nodules per plant was derived. This line was designated enf1 (enhanced nitrogen fixation 1).At 28 DAI, the number of nodules formed on enf1 roots was approximately 1.7 times greater than that of MG20, and the N fixation activity per enf1 plant was elevated 1.8 times over that of the wildtype plants. Because the N fixation activity per unit of enf1 nodule weight was also increased 1.7 times, we concluded that the increased N fixation activity was not solely due to the enhanced number of root nodules.The endogenous ABA concentration and the sensitivity to ABA of enf1 were lower than those of wild-type seedlings. ABA is believed to regulate early nodulation stages negatively by inhibiting Nod factor signaling, bacterial infection, and nodule initiation.^14,18 Elongated ITs were more common in enf1 root hairs at later stages of development (8–12 DAI). Furthermore, ITs were detected in nodule primordia more frequently in enf1 compared to MG20. These results suggest that the earliest stages of nodule development are not as strongly inhibited in enf1 as they are in wild-type MG20.Because enf1 had a low endogenous ABA concentration, we hypothesized that the decrease in ABA concentration caused the elevation of N fixation activity. To test this hypothesis, we treated wild-type plants at 28 DAI with 20 µM abamine, a specific inhibitor of ABA synthesis.¹⁹ After a three day-treatment period, acetylene reduction activity was measured. Such short treatment periods of abamine are not expected to induce new nodule development. Wild-type plants treated with abamine had a reduced endogenous ABA concentration in roots, to about one-fourth of the level of control plants. However, N fixation activity was elevated to about 170% over the non-treated controls (Fig. 1A and B). This result phenocopies enf1, which shows decreased endogenous ABA concentration as well as elevated N fixation activity. These results strongly suggest that the decrease in endogenous ABA concentration in enf1 was responsible for the increased levels of N fixation activity. Applying 0.5 µM ABA did not result in a further increase in N fixation activity even though the endogenous ABA concentrations are presumed to increase (Fig. 1A and B).Open in a separate windowFigure 1Effects of ABAconcentration on nitrogen fixation activity. M. loti-inoculated plants were grown for 28 days on vermiculite-filled pots supplied with B & D medium. Plant roots 28 DAI were treated with 0.5 µM ABA, 20 µM abamine, with both ABA and abamine, or were untreated (B & D medium control), respectively, for 3 days. (A) ARA per nodule weight. (B) ABA concentration in root. At least 15 plants were used in acetylene reduction assay. Four different plants were used for the measurement of ABA concentration and 3 repeats were performed. Error bars indicate the standard error, and the significance of differences between untreated control and treated values was determined by the two-tailed multiple t-test with Bonferroni correction following ANOVA (three comparisons in four groups), *p < 0.05, **p < 0.01.Nitric oxide (NO) is known as a strong inhibitor of N fixation activity,²⁰ as well as a signal component in ABA signaling pathway.^21,22 NO production in root nodules formed by enf1 21 DAI and 28 DAI was examined by using the fluorescent dye diaminofluorescein-FM (DAF-FM), a NO specific detector, and relative fluorescence unit (RFU) values were estimated. The RFU values of enf1 nodules 21 DAI were clearly decreased compared with that of MG20; this trend was more obvious at 28 DAI. Moreover, the effect of reduced ABA concentration caused by treatment with abamine on NO production was analyzed (Fig. 2). When nodules formed on the roots of 28-d-old plants were treated, the RFU value of the enf1 mutant was almost the same for (−) abamine and (+) abamine-treated, whereas, the RFU value of abamine-treated MG20 plants was significantly reduced compared to untreated MG20 (Fig. 2). These results strongly suggest that decreased production of NO caused by the low concentration of ABA in enf1 nodules was responsible for the increase in N fixation activity.Open in a separate windowFigure 2NO production in nodules. Quantification of nitric oxide in nodules that were treated with abamine. Nodules on the root of 28-day-old plants were treated with 20 µM abamine for 3 days. Relative fluorescent units (RFU) per nodule fresh weight at 515 nm, normalized against MG20 plants, are shown. The data represent the average ± standard error of 3 independent experiments derived from nodules of 6 to 8 plants. The significance of differences among the four groups was determined by the two-tailed multiple t-test with Bonferroni correction following ANOVA (six comparisons in four groups) and the different letters refer to significant differences at p < 0.01.Until now, the majority of symbiotic mutants that have been described represents loss of or defects in root nodule formation.^6,23,24 Many of these mutants induce nodules that are Fix-.^15–17 Although reports of mutants that show increased root nodule number^25–28 or spontaneous root nodule formation exist,^7,29 reports concerning mutations where N fixation activity is elevated without deleterious effects on plant growth and development are limited. One exception is the L. japonicus rdh1 mutant, which also exhibits a hypernodulation and enhanced nitrogen fixation phenotype.³⁰In this report, we have shown that mutating the ENF1 gene leads to an elevation of N fixation activity without accompanying adverse growth effects. In long-term growth experiments, some yield parameters were the same for both enf1 and wild-type plants, but both the dry weight and N content of 100 seeds and entire enf1 plants were significantly larger compared to those parameters in wild-type seeds and plants. These results strongly suggest that more nitrogen is fixed in the enf1 mutant than in wild-type plants. Therefore, this gene should be an important target for molecular breeding. We have determined that ENF1 gene is inherited in a monogenic and incompletely dominant manner. Our future work will identify the gene responsible for these positive growth effects.     

Gentamicin inhibits HSP70-assisted protein folding by interfering with substrate recognition

We previously reported that gentamicin (GM) specifically binds to heat-shock protein with subunit molecular masses of 70 kDa (HSP70). In the present study, we have investigated the effects of GM binding on HSP70-assisted protein folding in vitro. The C-terminal, and not the N-terminal of HSP70 was found to bind to GM. GM significantly suppressed refolding of firefly luciferase in the presence of HSP70 and HSP40, although the ATPase activity of HSP70 was unaffected by GM. A surface plasmon resonance analysis revealed that GM specifically interferes with the binding of HSP70 to a model peptide that mimics the exposed hydrophobic surface of the folding intermediates. These results indicated that GM inhibits the chaperone activity of HSP70 and may suppress protein folding via inhibition of HSP70 in vivo.

Structured summary

MINT-7384283: HSP40 (uniprotkb:P25685) binds (MI:0407) to HSP70 (uniprotkb:P34930) by surface plasmon resonance (MI:0107)MINT-7384430: RNaseA (uniprotkb:P61823) binds (MI:0407) to HSP70 (uniprotkb:P34930) by surface plasmon resonance (MI:0107)     

Cells from an anhydrobiotic chironomid survive almost complete desiccation

Dry-preservation of nucleated cells from multicellular animals represents a significant challenge in life science. As anhydrobionts can tolerate a desiccated state, their cells and organs are expected to show high desiccation tolerance in vitro. In the present study, we established cell lines derived from embryonic tissues of an anhydrobiotic chironomid, Polypedilum vanderplanki, designated as Pv11 and Pv210. Salinity stress induced the expression of a set of anhydrobiosis-related genes in both Pv11 and Pv210 cells, suggesting that at least a part of cells can autonomously control the physiological changes for the entry into anhydrobiosis. When desiccated with medium supplemented with 300 mM trehalose or sucrose and stored for 4 weeks in dry air (approximately 5% relative humidity), a small percentage of the cells was found to be viable upon rehydration, although surviving cells seemed not to be able to multiply. We also attempted dry-preservation of organs isolated from P. vanderplanki larvae, and found that a proportion of cells in some organs, including fat body, testis, nerve and dorsal vessel, tolerated in vitro desiccation.     

A novel complete reconstitution system for membrane integration of the simplest membrane protein

A complete reconstitution system for membrane integration of the simplest protein was developed by means of defined factors. A mutant version of Pf3 coat protein, 3L-Pf3 coat, requires neither signal recognition particle/Sec factors nor a membrane potential for its integration into the cytoplasmic membrane of Escherichia coli. Although 3L-Pf3 coat is spontaneously integrated into liposomes composed of phospholipids, diacylglycerol completely blocks such spontaneous integrations at a physiological level. Under the conditions where spontaneous integration does not occur, 3L-Pf3 coat integration was absolutely dependent on a novel integration-stimulating factor. Combination of the PURE system, an in vitro translation system composed of the purified factors involved in translation in E. coli, with liposomes containing the highly purified integration-stimulating factor revealed multiple cycles of 3L-Pf3 coat integration, achieving the complete reconstitution of membrane integration. Based on the function of the factor, we propose that the factor is named MPIase (Membrane Protein Integrase).