Symbiosis between Dendrobium catenatum protocorms and Serendipita indica involves the plant hypoxia response pathway.

Mycorrhizae are ubiquitous symbioses established between fungi and plant roots. Orchids, in particular, require compatible mycorrhizal fungi for seed germination and protocorm development. Unlike arbuscular mycorrhizal fungi, which have wide host ranges, orchid mycorrhizal fungi are often highly specific to their host orchids. However, the molecular mechanism of orchid mycorrhizal symbiosis is largely unknown compared to that of arbuscular mycorrhizal and rhizobial symbiosis. Here, we report that an endophytic Sebacinales fungus, Serendipita indica, promotes seed germination and the development of protocorms into plantlets in several epiphytic Epidendroideae orchid species (6 species in 2 genera), including Dendrobium catenatum, a critically endangered orchid with high medicinal value. Although plant-pathogen interaction and high meristematic activity can induce the hypoxic response in plants, it has been unclear whether interactions with beneficial fungi, especially mycorrhizal ones, also involve the hypoxic response. By studying the symbiotic relationship between D. catenatum and S. indica, we determined that hypoxia-responsive genes, such as those encoding alcohol dehydrogenase (ADH), are highly induced in symbiotic D. catenatum protocorms. In situ hybridization assay indicated that the ADH gene is predominantly expressed in the basal mycorrhizal region of symbiotic protocorms. Additionally, the ADH inhibitors puerarin and 4-methylpyrazole both decreased S. indica colonization in D. catenatum protocorms. Thus, our study reveals that S. indica is widely compatible with orchids and that ADH and its related hypoxia-responsive pathway are involved in establishing successful symbiotic relationships in germinating orchids.

Proteasome Dysfunction Leads to Suppression of the Hypoxic Response Pathway in Arabidopsis.

Proteasome is a large proteolytic complex that consists of a 20S core particle (20SP) and 19S regulatory particle (19SP) in eukaryotes. The proteasome degrades most cellular proteins, thereby controlling many key processes, including gene expression and protein quality control. Proteasome dysfunction in plants leads to abnormal development and reduced adaptability to environmental stresses. Previous studies have shown that proteasome dysfunction upregulates the gene expression of proteasome subunits, which is known as the proteasome bounce-back response. However, the proteasome bounce-back response cannot explain the damaging effect of proteasome dysfunction on plant growth and stress adaptation. To address this question, we focused on downregulated genes caused by proteasome dysfunction. We first confirmed that the 20SP subunit PBE is an essential proteasome subunit in Arabidopsis and that PBE1 mutation impaired the function of the proteasome. Transcriptome analyses showed that hypoxia-responsive genes were greatly enriched in the downregulated genes in pbe1 mutants. Furthermore, we found that the pbe1 mutant is hypersensitive to waterlogging stress, a typical hypoxic condition, and hypoxia-related developments are impaired in the pbe1 mutant. Meanwhile, the 19SP subunit rpn1a mutant seedlings are also hypersensitive to waterlogging stress. In summary, our results suggested that proteasome dysfunction downregulated the hypoxia-responsive pathway and impaired plant growth and adaptability to hypoxia stress.

UBA domain protein SUF1 interacts with NatA-complex subunit NAA15 to regulate thermotolerance in Arabidopsis.

During recovery from heat stress, plants clear away the heat-stress-induced misfolded proteins through the ubiquitin-proteasome system (UPS). In the UPS, the recognition of substrate proteins by E3 ligase can be regulated by the N-terminal acetyltransferase A (NatA) complex. Here, we determined that Arabidopsis STRESS-RELATED UBIQUITIN-ASSOCIATED-DOMAIN PROTEIN FACTOR 1 (SUF1) interacts with the NatA complex core subunit NAA15 and positively regulates NAA15. The suf1 and naa15 mutants are sensitive to heat stress; the NatA substrate N SNC1 is stabilized in suf1 mutant plants during heat stress recovery. Therefore, SUF1 and its interactor NAA15 play important roles in basal thermotolerance in Arabidopsis.

High Ambient Temperature Regulated the Plant Systemic Response to the Beneficial Endophytic Fungus Serendipita indica.

Most plants in nature establish symbiotic associations with endophytic fungi in soil. Beneficial endophytic fungi induce a systemic response in the aboveground parts of the host plant, thus promoting the growth and fitness of host plants. Meanwhile, temperature elevation from climate change widely affects global plant biodiversity as well as crop quality and yield. Over the past decades, great progresses have been made in the response of plants to high ambient temperature and to symbiosis with endophytic fungi. However, little is known about their synergistic effect on host plants. The endophytic fungus Serendipita indica colonizes the roots of a wide range of plants, including Arabidopsis. Based on the Arabidopsis-S. indica symbiosis experimental system, we analyzed the synergistic effect of high ambient temperature and endophytic fungal symbiosis on host plants. By transcriptome analysis, we found that DNA replication-related genes were significantly upregulated during the systemic response of Arabidopsis aboveground parts to S. indica colonization. Plant hormones, such as jasmonic acid (JA) and ethylene (ET), play important roles in plant growth and systemic responses. We found that high ambient temperature repressed the JA and ET signaling pathways of Arabidopsis aboveground parts during the systemic response to S. indica colonization in roots. Meanwhile, PIF4 is the central hub transcription factor controlling plant thermosensory growth under high ambient temperature in Arabidopsis. PIF4 is also involving JA and/or ET signaling pathway. We found that PIF4 target genes overlapped with many differentially expressed genes (DEGs) during the systemic response, and further showed that the growth promotion efficiency of S. indica on the pif4 mutant was higher than that on the wild-type plants. In short, our data showed that high ambient temperature strengthened the growth promotion effect of S. indica fungi on the aboveground parts of the host plant Arabidopsis, and the growth promotion effect of the systemic response under high ambient temperature was regulated by PIF4.

Chromatin remodeling factors regulate environmental stress responses in plants.

Environmental stress from climate change and agricultural activity threatens global plant biodiversity as well as crop yield and quality. As sessile organisms, plants must maintain the integrity of their genomes and adjust gene expression to adapt to various environmental changes. In eukaryotes, nucleosomes are the basic unit of chromatin around which genomic DNA is packaged by condensation. To enable dynamic access to packaged DNA, eukaryotes have evolved Snf2 (sucrose nonfermenting 2) family proteins as chromatin remodeling factors (CHRs) that modulate the position of nucleosomes on chromatin. During plant stress responses, CHRs are recruited to specific genomic loci, where they regulate the distribution or composition of nucleosomes, which in turn alters the accessibility of these loci to general transcription or DNA damage repair machinery. Moreover, CHRs interplay with other epigenetic mechanisms, including DNA methylation, histone modifications, and deposition of histone variants. CHRs are also involved in RNA processing at the post-transcriptional level. In this review, we discuss major advances in our understanding of the mechanisms by which CHRs function during plants' response to environmental stress.

Histone H3K4 methyltransferases SDG25 and ATX1 maintain heat-stress gene expression during recovery in Arabidopsis.

Plants have short-term stress memory that enables them to maintain the expression state of a substantial subset of heat-inducible genes during stress recovery after heat stress. Little is known about the molecular mechanisms controlling stress-responsive gene expression at the recovery stage in plants, however. In this article, we demonstrate that histone H3K4 methyltransferases SDG25 and ATX1 are required for heat-stress tolerance in Arabidopsis. SDG25 and ATX1 are not only important for stress-responsive gene expression during heat stress, but also for maintaining stress-responsive gene expression during stress recovery. A combination of whole-genome bisulfite sequencing, RNA-sequencing and ChIP-qPCR demonstrated that mutations of SDG25 and ATX1 decrease histone H3K4me3 levels, increase DNA cytosine methylation and inhibit the expression of a subset of heat stress-responsive genes during stress recovery in Arabidopsis. ChIP-qPCR results confirm that ATX1 binds to chromatins associated with these target genes. Our results reveal that histone H3K4me3 affects DNA methylation at regions in the loci associated with heat stress-responsive gene expression during stress recovery, providing insights into heat-stress transcriptional memory in plants.

The ß5 subunit is essential for intact 26S proteasome assembly to specifically promote plant autotrophic growth under salt stress.

The ubiquitin 26S proteasome (26SP) system efficiently degrades many key regulators of plant development. 26SP consists of two subcomplexes: the catalytic 20S core particle (CP) and the 19S regulatory particle (RP). Previous studies have focused on 19S RP; whether there is a specific subunit in 20S CP that has a stress-related biological function in plants is unclear. PBE1, one of the ß5 subunits of Arabidopsis proteasome CP, is essential for the assembly and proteolytic activity of 26SP in salt-stressed seedlings. The expression of PBE1 is stress-induced. During the transition from seed germination to autotrophic growth in salt-stressed seedlings, loss of PBE1 function results specifically in arrest in developmental transition but not in germination and post-germination growth. PBE1 is also important for other types of proteasome stress and Endoplasmic Reticulum (ER) stress. PBE1 modulates the protein level of the transcription factor ABI5 and thereby down-regulates the expression of several genes downstream of this key regulator which are known to be essential for plant growth under stress. Collectively, our results showed PBE1-mediated intact proteasome assembly that is essential for successful autotrophic growth, and revealed how PBE1 mediated stress proteasome functions to control both proteasome activity and abscisic acid (ABA)-mediated stress signaling in plants.

Two B-Box Domain Proteins, BBX18 and BBX23, Interact with ELF3 and Regulate Thermomorphogenesis in Arabidopsis.

Plants coordinate their growth and developmental programs with various endogenous signals and environmental challenges. Phytochrome interacting factor 4 (PIF4) plays a critical positive role in thermoresponsive gene expression and hypocotyl growth in Arabidopsis, whereas early flowering 3 (ELF3) negatively regulates the activity of PIF4 at elevated temperatures. However, it is unknown how ELF3 activity is regulated at warm temperatures. Here, we report the identification of B-box 18 (BBX18) and BBX23 as important thermomorphogenesis regulators in Arabidopsis. BBX18 and BBX23 mutations result in reduced thermoresponsive hypocotyl elongation. In contrast, BBX18 overexpression promotes hypocotyl growth at elevated temperatures, which depends on either PIF4 or constitutive photomorphogenic 1 (COP1). BBX18 and BBX23 interact with ELF3 or COP1. Knocking out BBX18 and BBX23 increases ELF3 abundance under normal and warm temperature conditions. The expression of multiple thermoresponsive genes is impaired in both a PIF4 mutant and a BBX18/BBX23 double mutant. Thus, our findings reveal an important role of B-box proteins during thermomorphogenesis and provide insights into our understanding of how warm temperature signals regulate ELF3 activity and PIF4-dependent genes.

Chromatin remodeling factor CHR18 interacts with replication protein RPA1A to regulate the DNA replication stress response in Arabidopsis.

DNA replication is a fundamental process for the faithful transmission of genetic information in all living organisms. Many endogenous and environmental signals impede fork progression during DNA synthesis, which induces replication errors and DNA replication stress. Chromatin remodeling factors regulate nucleosome occupancy and the histone composition of the nucleosome in chromatin; however, whether chromatin remodeling factors are involved in the DNA replication stress response in plants is unknown. We reveal that chromatin remodeling factor CHR18 plays important roles in DNA replication stress in Arabidopsis thaliana by interacting with the DNA replication protein RPA1A. According to the genetic analysis, the loss of function of either CHR18 or RPA1A confers a high sensitivity to DNA replication stress in Arabidopsis. CHR18 interacts with RPA1A in both yeast cells and tobacco epidermal cells. The coexpression of RPA1A and CHR18 enhances the accumulation of CHR18 in nuclear foci in plants. CHR18 is a typical nuclear-localized chromatin remodeling factor with ATPase activity. Our results demonstrate that during DNA synthesis in plants, RPA1A interacts with CHR18 and recruits CHR18 to nuclear foci to resolve DNA replication stress, which is important for cell propagation and root growth in Arabidopsis plants.

Influence of microstructural features on thermal expansion coefficient in graphene/epoxy composites.

In this paper, theoretical calculations were conducted to determine the coefficient of thermal expansion (CTE) based on the effective medium approach using Green's function method. The influences of microstructural features were investigated, including volume fraction, aspect ratio, and the orientation of graphene fillers. Calculated results demonstrated strong anisotropy of CTE when all graphene sheets in the composite were aligned in the in-plane direction due to the large difference between the elastic moduli of the graphene and epoxy. The in-plane CTE in the graphene/epoxy composite can be effectively reduced with small additions of graphene additive. Orientation dispersion among the graphene fillers significantly decreases the anisotropy of CTE. Accounting for the influences of all microstructural features, simulation results closely align with current experimental results. This work will provide a general guideline and a solid foundation for the optimal design and preparation of graphene/polymer composites.

[Comparison of the IL-27 level in gingival crevicular fluid of cross-quadrant and the upper and lower half-mouth subgingival scaling].

PURPOSE: To investigate the changes of IL-27 in gingival crevicular fluid (GCF) before and after treatment with different methods for chronic periodontitis. METHODS: Sixty patients with moderate or severe chronic periodontitis were selected as study group to divide into group A (cross-quadrant) and group B (upper and lower half-mouth) randomly. Another 30 healthy people were selected as group C. Gingival crevicular fluid of group A and B were collected at baseline and each week during treatment. At the same time, the clinical parameters including PD, AL, BI and PLI were recorded. And the levels of IL-27 in GCF were measured by ELISA. SPSS 17.0 software package was used for statistical analysis. RESULTS: The levels of IL-27 in GCF 2 and 3 weeks after treatment were higher in study group compared with those at baseline, while PD, AL, BI and PLI showed significant reduction. The changes except PLI in group A was more obvious than group B, which had a significant difference. After three-week treatment, IL-27 in group A had no remarkable difference compared with group C. There were significantly negative correlation between PD, AL, BI, PLI and IL-27. CONCLUSIONS: IL-27 in GCF can be considered as a potential target for prevention and treatment of chronic periodontitis. Compared with the upper and lower half-mouth subgingival scaling, cross-quadrant has more pronounced short-term effect.

The proteasome is responsible for caspase-3-like activity during xylem development.

Xylem development is a process of xylem cell terminal differentiation that includes initial cell division, cell expansion, secondary cell wall formation and programmed cell death (PCD). PCD in plants and apoptosis in animals share many common characteristics. Caspase-3, which displays Asp-Glu-Val-Asp (DEVD) specificity, is a crucial executioner during animal cells apoptosis. Although a gene orthologous to caspase-3 is absent in plants, caspase-3-like activity is involved in many cases of PCD and developmental processes. However, there is no direct evidence that caspase-3-like activity exists in xylem cell death. In this study, we showed that caspase-3-like activity is present and is associated with secondary xylem development in Populus tomentosa. The protease responsible for the caspase-3-like activity was purified from poplar secondary xylem using hydrophobic interaction chromatography (HIC), Q anion exchange chromatography and gel filtration chromatography. After identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS), it was revealed that the 20S proteasome (20SP) was responsible for the caspase-3-like activity in secondary xylem development. In poplar 20SP, there are seven α subunits encoded by 12 genes and seven ß subunits encoded by 12 genes. Pharmacological assays showed that Ac-DEVD-CHO, a caspase-3 inhibitor, suppressed xylem differentiation in the veins of Arabidopsis cotyledons. Furthermore, clasto-lactacystin ß-lactone, a proteasome inhibitor, inhibited PCD of tracheary element in a VND6-induced Arabidopsis xylogenic culture. In conclusion, the 20S proteasome is responsible for caspase-3-like activity and is involved in xylem development.

Quantum key distribution based on phase encoding in long-distance communication fiber.

A robust two-way quantum key distribution system based on phase encoding is demonstrated in 50 km and 100 km commercial communication fiber. The system can automatically compensate for birefringence effects and remain stable over 23 h. A low quantum bit error rate and high visibility are obtained. Furthermore, the storage fiber is unnecessary and train of pulses is only needed in the test with 100 km fiber.