Transcriptome analysis reveals the potential mechanism of the response to scale insects in Camellia sasanqua Thunb.

BACKGROUND: Camellia sasanqua Thunb. is an essential woody ornamental plant. Our continuous observation found that scale insects often infest C. sasanqua all year round in Kunming, China, resulting in poor growth. Scientifically preventing and controlling the infestation of scale insects should be paid attention to, and the mechanism of scale insects influencing C. sasanqua should be used as the research basis. RESULTS: The scale insect was identified as Pseudaulacaspis sasakawai Takagi. We analyzed transcriptome sequencing data from leaves of C. sasanqua infested with scale insects. A total of 1320 genes were either up-regulated or down-regulated and differed significantly in response to scale insects. GO (Gene Ontology) annotation analysis showed that the pathway of catalytic activity, binding, membrane part, cell part, and cellular process were affected. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that most DEGs (differentially expressed genes) involved in plant hormone signal transduction, MAPK signaling pathway, flavonoid biosynthesis, tropane, piperidine and pyridine alkaloid biosynthesis. We also observed that the expression of galactose metabolism and carotenoid biosynthesis were significantly influenced. In addition, qRT-PCR (quantitative real-time PCR) validated the expression patterns of DEGs, which showed an excellent agreement with the transcriptome sequencing. CONCLUSIONS: Our transcriptomic analysis revealed that the C. sasanqua had an intricate resistance strategy to cope with scale insect attacks. After sensing the attack signal of scale insects, C. sasanqua activated the early signal MAPK (mitogen-activated protein kinase) to activate further transcription factors and Auxin, ET, JA, ABA, and other plant hormone signaling pathways, ultimately leading to the accumulation of lignin, scopolin, flavonoids and other secondary metabolites, produces direct and indirect resistance to scale insects. Our results suggested that it provided some potential resources of defense genes that would benefit the following resistance breeding in C. sasanqua to scale insects.

Identification, molecular profiling and immune functions of cystatin M in silver pomfret (Pampus argenteus).

Cystatins play an important role in various physiological and pathological processes of organisms, including regulating protein metabolism, antigen processing, inflammatory response, nutritional disorders, and controlling enzyme activity. However, research on immunity functions of fish cystatin M is limited. In this study, Pampus argenteus cystatin M (Pacystatin M) was identified and analyzed. Its amino acid sequence was highly conserved in teleosts, and included the conserved cystatin cysteine protease inhibitor motifs. Pacystatin M was highly expressed in the gill, spleen, and intestine, whereas the expression levels of liver and kidney were lower. Furthermore, Nocardia seriolae infection up-regulated the expression of Pacystatin M in the kidney, spleen and liver, with particularly significant expression observed in the liver on day 15 post-infection. Functional analysis indicated that the recombinant Pacystatin M showed increasing inhibitory activity against papain within a certain concentration range, suggesting that the inhibition was likely competitive. Additionally, Pacystatin M demonstrated the ability to inhibit bacterial growth and high thermal stability. These results suggested that Pacystatin M might be involved in the immune response to microbial invasion and provided new reference addressing disease issues in the large-scale farming of silver pomfret.

Identification of COMMD gene family in large yellow croaker (Larimichthys crocea): Immune response induced by Pseudomonas plecoglossicida infection and acute hypoxia stress.

The COMMD (Copper Metabolism gene MURR1 Domain) gene family consists of 10 members, which are involved in various biological processes such as copper and sodium transport, NF-κB activity and cell cycle progression. However, the study of COMMD gene family in large yellow croaker (Larimichthys crocea) is largely unknown. In this study, 10 COMMD gene family members (named LcCOMMDs) were successfully identified from large yellow croaker. The results showed that there were differences in the number of LcCOMMDs exons at the level of gene structure, which reflected that they had adjusted and changed accordingly in the process of evolution to adapt to the environment and achieved functional diversification. Through phylogenetic analysis, we found that the LcCOMMDs was highly conserved, indicating their important functions in organisms. It was worth noting that the expression levels of LcCOMMD1, LcCOMMD2, LcCOMMD3, LcCOMMD5 and LcCOMMD10 in the spleen changed significantly after bacterial stress, which suggested that these genes might be involved in the regulation of innate immune response. In addition, the expression levels of LcCOMMD1, LcCOMMD2, LcCOMMD3, LcCOMMD5, LcCOMMD7, LcCOMMD8, LcCOMMD9 and LcCOMMD10 changed significantly after hypoxia exposure, which further proved the role of LcCOMMDs in immune function. In summary, this study not only revealed the important role of COMMD genes in the innate immune response of large yellow croaker, but also provided valuable information for further understanding the regulatory mechanism of COMMD gene family under different conditions.

Genome-wide identification and characterization of large yellow croaker (Larimichthys crocea) suppressors of cytokine signaling (SOCS) in immune response to Pseudomonas plecoglossicida infection and acute hypoxia stress.

The suppressor of cytokine signaling (SOCS) gene family is a group of genes involved in the negative regulation of cytokine signal transduction. The members of this family play a crucial role in regulating immune and inflammatory processes. However, comprehensive investigations of these genes have not yet been conducted in the economically significant fish large yellow croaker (Larimichthys crocea). In this study, a total of 13 SOCS genes (LcSOCS1a, LcSOCS1b, LcSOCS2, LcSOCS3a, LcSOCS3b, LcSOCS4, LcSOCS5a, LcSOCS5b, LcSOCS6, LcSOCS7a, LcSOCS7b, LcCISHa and LcCISHb) were identified and analyzed in L. crocea. The phylogenetic tree revealed a high conservation of SOCS genes in evolution, and the gene structure and motif analysis indicated a high similarity in the structure of LcSOCSs in the same subfamily. In addition, the expression patterns of LcSOCSs showed that LcSOCS1b was significantly down-regulated in all time under acute hypoxia stress, but it was markedly up-regulated throughout the entire process after P. plecoglossicida infection, revealing its different immune effects to two stresses. Besides, LcSOCS2a, LcSOCS6 and LcSOCS7a only participated in acute hypoxic stress, while LcSOCS5a was more sensitive to P. plecoglossicida infection. In summary, these results indicated that SOCS genes were involved in stress responses to both biological and non-biological stimuli, setting the foundation for deeper study on the functions of SOCS genes.

Identification of large yellow croakers (Larimichthys crocea) scavenger receptor genes: Involvement in immune response to Pseudomonas plecoglossicida infection and hypoxia-exposure experiments.

Scavenger receptors (SRs) are pattern recognition receptors involved in the innate immune defense against pathogen infection in fish. However, there has not been much research done on teleosts. In this study, 18 members of the SR gene family were found in large yellow croaker. The identification of the SR gene family showed that the protein length of SR members in large yellow croaker were quite different, and most SR genes were distributed in nuclear and endoplasmic. The evolutionary relationship, exon/intron structure and motif analysis revealed that members of the SR gene family were highly conserved. The results of the expression profiles after Pseudomonas plecoglossicida infection and hypoxia-exposure demonstrated that SR members were involved in inflammatory reactions. Especially, COLEC12 and SCARF1 exhibited substantial changes in response to both P. plecoglossicida and hypoxia stress, indicating their possible immunological functions. The result of this study revealed that SR genes played a vital part in the innate immune response of large yellow croaker, and would give important details for a deeper comprehension of the SR gene family's regulation mechanism under various conditions in large yellow croaker.

Transforming growth factor-ß (TGF-ß): A master signal pathway in teleost sex determination.

Sex determination and differentiation in fish has always been a hot topic in genetic breeding of aquatic animals. With the advances in next-generation sequencing (NGS) in recent years, sex chromosomes and sex determining genes can be efficiently identified in teleosts. To date, master sex determination genes have been elucidated in 114 species, of which 72 species have sex determination genes belonging to TGF-ß superfamily. TGF-ß is the only signaling pathway that the largest proportion of components, which including ligands (amhy, gsdfy, gdf6), receptors (amhr, bmpr), and regulator (id2bby), have opportunity recognized as a sex determination gene. In this review, we focus on the recent studies about teleost sex-determination genes within TGF-ß superfamily and propose several hypotheses on how these genes regulate sex determination process. Differing from other reviews, our review specifically devotes significant attention to all members of the TGF-ß signal pathway, not solely the sex determination genes within the TGF-ß superfamily. However, the functions of the paralogous genes of TGF superfamily are still needed ongoing research. Further studies are required to more accurately interpret the molecular mechanism of TGF-ß superfamily sex determination genes.

Cyp19a1a Promotes Ovarian Maturation through Regulating E2 Synthesis with Estrogen Receptor 2a in Pampus argenteus (Euphrasen, 1788).

In the artificial breeding of Pampus argenteus (Euphrasen, 1788), female fish spawn before male release sperm, which indicates rapid ovarian development. In fish, aromatase is responsible for converting androgens into estrogens and estrogen plays a crucial role in ovarian development. In this study, we aimed to investigate the potential role of brain-type and ovarian-type aromatase to study the rapid ovarian development mechanism. The results showed that cyp19a1a was mainly expressed in the ovary and could be classified as the ovarian type, whereas cyp19a1b could be considered as the brain type for its expression was mainly in the brain. During ovarian development, the expression of cyp19a1a in the ovary significantly increased from stage IV to stage V and Cyp19a1a signals were present in the follicle cells, while cyp19a1b expression in the pituitary gland decreased from stage IV to stage V. To further investigate the function of Cyp19a1a, recombinant Cyp19a1a (rCyp19a1a) was produced and specific anti-Cyp19a1a antiserum was obtained. The expressions of cyp19a1a, estrogen receptors 2 alpha (esr2a), and androgen receptor alpha (arα) were significantly upregulated in the presence of rCyp19a1a. Meanwhile, cyp19a1a was expressed significantly after E2 treatment in both ovarian and testicular tissue culture. Taken together, we found two forms of aromatase in silver pomfret. The ovarian-type aromatase might play an important role in ovarian differentiation and maturation, and participate in E2 synthesis through co-regulation with esr2a. The brain-type aromatase cyp19a1b might be involved in the regulation of both brain and gonadal development.

Transcriptome analysis reveals core lncRNA-mRNA networks regulating melanization and biomineralization in Patinopecten yessoensis shell-infested by Polydora.

BACKGROUND: Patinopecten yessoensis, a large and old molluscan group, has been one of the most important aquaculture shellfish in Asian countries because of its high economic value. However, the aquaculture of the species has recently been seriously affected by the frequent outbreaks of Polydora disease, causing great economic losses. Long non-coding RNAs (lncRNAs) exhibit exhibit crucial effects on diverse biological processes, but still remain poorly studied in scallops, limiting our understanding of the molecular regulatory mechanism of P. yessoensis in response to Polydora infestation. RESULTS: In this study, a high-throughput transcriptome analysis was conducted in the mantles of healthy and Polydora-infected P. yessoensis by RNA sequencing. A total of 19,133 lncRNAs with 2,203 known and 16,930 novel were identified. The genomic characterizations of lncRNAs showed shorter sequence and open reading frame (ORF) length, fewer number of exons and lower expression levels in comparison with mRNAs. There were separately 2280 and 1636 differentially expressed mRNAs and lncRNAs (DEGs and DELs) detected in diseased individuals. The target genes of DELs were determined by both co-location and co-expression analyses. Functional enrichment analysis revealed that DEGs involved in melanization and biomineralization were significantly upregulated; further, obviously increased melanin granules were observed in epithelial cells of the edge mantle in diseased scallops by histological and TEM study, indicating the crucial role of melanizaiton and biomineralization in P. yessoensis to resist against Polydora infestation. Moreover, many key genes, such as Tyrs, Frizzled, Wnts, calmodulins, Pifs, perlucin, laccase, shell matrix protein, mucins and chitins, were targeted by DELs. Finally, a core lncRNA-mRNA interactive network involved in melanization and biomineralization was constructed and validated by qRT-PCR. CONCLUSIONS: This work provides valuable resources for studies of lncRNAs in scallops, and adds a new insight into the molecular regulatory mechanisms of P. yessoensis defending against Polydora infestation, which will contribute to Polydora disease control and breeding of disease-resistant varieties in molluscs.

3D Covalent Organic Framework as a Metastable Intermediate in the Formation of a Double-Stranded Helical Covalent Polymer.

The design and development of intricate artificial architectures have been pursued for decades. Helical covalent polymer (HCP) was recently reported as an unexpected topology that consists of chiral 1D polymers assembled through weak hydrogen bonds from achiral building blocks. However, many questions remained about the formation, driving force, and the single-handedness observed in each crystal. In this work, we reveal a metastable, racemic, fully covalently cross-linked, 3D covalent organic framework (COF) as an intermediate in the early stage of polymerization, which slowly converts into single-handed HCP double helices through partial fragmentation and self-sorting with the aid of a series of hydrogen bonding. Our work provides an intriguing example where weak noncovalent bonds serve as the determining factor of the overall product structure and facilitate the formation of a sophisticated polymeric architecture.

Characterization of Japanese flounder (Paralichthys olivaceus) STAT members: An immune-related gene family involved in Edwardsiella tarda and temperature stress.

The signal transducer and activator of transcription (STAT) family members are not only the transcriptional activators, but also play important roles in regulating inflammatory response. Some members have been reported to be involved in innate bacterial and antiviral immunity in aquatic organisms. However, no systematic research on STATs has been found in teleost. In this present study, we characterized six STAT genes in Japanese flounder based on bioinformatics methods, namely PoSTAT1, PoSTAT2, PoSTAT3, PoSTAT4, PoSTAT5 and PoSTAT6. The phylogenetic analysis of STATs in fish indicated that STATs were highly conserved and revealed an absence of STAT5 in a few species. Further analysis of gene structures and motifs showed STAT proteins shared a similar structure and probably had similar functionality in Japanese flounder. The expression profiles of different development stages and tissues demonstrated that PoSTATs exhibited specificity in temporality and spatiality as well as PoSTAT4 was highly expressed in gill. The transcriptome data analysis of E. tarda and temperature stress showed that PoSTAT1 and PoSTAT2 were more respective to these two kinds of stress. In addition, the results also demonstrated that these PoSTATs might regulate immune response in different ways, manifested by up-regulation in E. tarda infection and down-regulation in temperature stress. In a word, this systematic analysis of PoSTATs would provide valuable information about the phylogenetic relationship of STATs in fish species and help understand the role of STAT genes in the immune response of Japanese flounder.

Characterisation, evolution and expression analysis of the interferon regulatory factor (IRF) family from olive flounder (Paralichthys olivaceus) in response to Edwardsiella tarda infection and temperature stress.

Interferon regulatory factor (IRF) family involves in the transcriptional regulation of type I Interferons (IFNs) and IFN-stimulated genes (ISGs) and plays a critical role in cytokine signaling and immune response. However, systematic identification of the IRF gene family in teleost has been rarely reported. In this study, twelve IRF members, named PoIRF1, PoIRF2, PoIRF3, PoIRF4a, PoIRF4b, PoIRF5, PoIRF6, PoIRF7, PoIRF8, PoIRF9, PoIRF10 and PoIRF11, were identified from genome-wide data of olive flounder (Paralichthys olivaceus). Phylogenetic analysis indicated that PoIRFs could be classified into four clades, including IRF1 subfamily (PoIRF1, PoIRF11), IRF3 subfamily (PoIRF3, PoIRF7), IRF4 subfamily (PoIRF4a, PoIRF8, PoIRF9, PoIRF10) and IRF5 subfamily (PoIRF5, PoIRF6). They were evolutionarily related to their counterparts in other fish. Gene structure and motif analysis showed that PoIRFs protein sequences were highly conserved. Under normal physiological conditions, all PoIRFs were generally expressed in multiple developmental stages and healthy tissues. After E. tarda attack and temperature stress, twelve PoIRFs showed significant and different changes in mRNA levels. The expression of PoIRF1, PoIRF3, PoIRF4a, PoIRF5, PoIRF7, PoIRF8, PoIRF9, PoIRF10 and PoIRF11 could be markedly induced by E. tarda, indicating that they played a key role in the process of antibacterial immunity. Besides, temperature stress could significantly stimulate the expression of PoIRF3, PoIRF5, PoIRF6 and PoIRF7, indicating that they could transmit signals rapidly when the temperature changes. In conclusion, this study reported the molecular properties and expression analysis of PoIRFs, and explored their role in immune response, which laid a favorable foundation for further studies on the evolution and functional characteristics of the IRF family in teleost fish.

Identification of the matrix metalloproteinase (MMP) gene family in Japanese flounder (Paralichthys olivaceus): Involved in immune response regulation to temperature stress and Edwardsiella tarda infection.

The Matrix metalloproteinase (MMP) gene family is responsible for regulating the degradation of Extra Cellular Matrix (ECM) proteins, which are important for physiological processes such as wound healing, tissue remodeling, and stress response. Although MMPs have been studied in many species, their role in immune response in Japanese flounder (Paralichthys olivaceus) is still not fully understood. This study conducted a comprehensive analysis of MMPs in flounder, including gene structures, evolutionary relationships, conserved domains, molecular evolution, and expression patterns. Analysis revealed that MMP genes could be grouped into 17 subfamilies and were evolutionarily conserved and functionally-constrained. Meanwhile, MMP genes were found to express in different embryonic and larval stages and might play the role of sentinel in healthy tissues. Furthermore, expression profiling showed that MMPs had diverse functions in environmental stress, with 60% (9/15) and 73% (11/15) of MMPs showing differential expression patterns under temperature stress and Edwardsiella tarda (E. tarda) infection, respectively. These findings provide a useful resource for understanding the immune functions of MMP genes in Japanese flounder.

Genome-wide identification of TNF receptor-associated factors in Japanese flounder (Paralichthys olivaceus) and functional analysis of resistance to temperature and Edwardsiella tarda stress.

Tumor necrosis factor receptor-associated factors (TRAFs), as the signaling mediators of the tumor necrosis factor (TNFR) superfamily, toll-like receptors (TLR) and interleukin-1 receptor (IL-1R) superfamily, can activate downstream signal transduction pathways and play an important role in the body's immune process. In this study, six TRAF genes, namely PoTRAF2a, PoTRAF2b, PoTRAF3, PoTRAF4, PoTRAF6 and PoTRAF7, were identified and annotated in Japanese flounder by using bioinformatics methods. Phylogenetic analysis confirmed that TRAF genes can be divided into seven groups. Analysis of motif composition and gene structure demonstrated that all PoTRAF members were evolutionarily conserved. The expression patterns of PoTRAF genes were then further investigated in six different developmental stages and eleven tissues of healthy fish, and it was found that there were spatial and tissue specificities among the members. To investigate the immune response of Japanese flounder to abiotic and biotic stresses, we further analyzed the expression profile of PoTRAFs after temperature stress and pathogen challenge. The result showed that PoTRAF3 and PoTRAF4 were observably differentially expressed under temperature stress, indicating that they were involved in the immune response after temperature stress. The expression of PoTRAF2a, PoTRAF2b and PoTRAF4 was significantly different after E. tarda infection, suggesting that they might have antibacterial effects. These results would help to clarify the molecular roles of PoTRAF genes in the regulation of immune and inflammatory responses in Japanese flounder.

Genome-wide identification of olive flounder (Paralichthys olivaceus) SOCS genes: Involvement in immune response regulation to temperature stress and Edwardsiella tarda infection.

The suppressors of cytokine signaling (SOCS) gene family participates in development and immunity through negative regulation of cytokine signaling pathways. Although the immune response of SOCS gene family members has been extensively characterized in teleost, no similar study has been reported in olive flounder yet. In our present study, a total of 13 SOCSs in olive flounder were identified and characterized systematically. By querying the SOCS sequences of ten teleost fish species, we found there were exactly more members of SOCSs in fish than mammals, which indicated that there were more duplication events occurred in fish than in higher vertebrates. Phylogenetic analysis clearly illuminated that SOCS genes were highly conserved. The analysis of gene structure and motif showed SOCS proteins of olive flounder shared a high level of sequence similarity strikingly. The expression profiles of tissues and developmental stages indicated that SOCS members had a kind of specificity in temporality and spatiality. RNA-Seq analysis of temperature stress and E. Tarda infection demonstrated SOCS members were involved in inflammatory response. In a word, our results would provide a further reference for understanding the mechanism of SOCS genes in olive flounder.

Identification of olive flounder (Paralichthys olivaceus) toll-like receptor genes: Involvement in immune response to temperature stress and Edwardsiella tarda infection.

Toll-like receptor (TLR) genes are best known for their roles in the innate immune defense. However, studies focusing on the reaction mechanisms of TLR genes in olive flounder (Paralichthys olivaceus) immune responses are still limited. In this study, 11 TLR family members (PoTLRs) were identified and classified from P. olivaceus genome. Phylogenetic analysis showed that PoTLRs were highly conserved in olive flounder. The analysis of motif prediction and gene structure indicated that TLRs had high sequence similarity. The expression patterns in developmental stages and different tissues showed that TLR members were spatially and temporally specific. RNA-Seq analysis of temperature stress and Edwardsiella tarda infection suggested that TLR members were involved in inflammatory responses, PoTLR5b and PoTLR22 showed significant differences in response to both temperature stress and E. tarda stress, indicating their potential immune functions. The results of this study suggested that TLR genes played important roles in the innate immune response of olive flounder, and would provide a solid basis for further study of their functions.

Identification and characterization of toll-like receptor genes in silver pomfret (Pampus argenteus) and their involvement in the host immune response to Photobacterium damselae subsp. Damselae and Nocardia seriolae infection.

Toll-like receptors (TLRs) are vital pattern recognition receptors that play a critical role in the innate immune response against pathogenic attack. Among the bacteria commonly found in the culture process of silver pomfret, Photobacterium damselae subsp. Damselae (PDD, gram-negative) and Nocardia seriolae (NS, gram-positive), can cause large-scale mortality in this fish species. However, there is currently no research on the role of TLRs in mediating the immune response of silver pomfret to these two bacterial infections. Therefore, in this study, we identified nine PaTLRs family members, including several fish-specific TLRs (TLR14 and TLR21). Phylogenetic analysis revealed that these PaTLRs genes could be classified into five subfamilies, namely TLR1, TLR3, TLR5, TLR7, and TLR11, indicating their evolutionary conservation. To further explore the interactions of TLR genes with immune-related mediators, protein and protein interaction network (PPI) results were generated to explain the association of TLR genes with TNF receptor-associated factor 6 (TRAF6) and other relevant genes in the MyD88-dependent pathway and NF-κb signaling pathway. Subsequently, RT-qPCR was conducted to verify the expression patterns of the nine TLR genes in the gills, skin, kidney, liver, and spleen of healthy fish, with most of the TLRs showing high expression levels in the spleen. Following infection with PDD and NS, these PaTLRs exhibited different expression patterns in the spleen, with PaTLR2, PaTLR3, PaTLR5, PaTLR7, PaTLR9, and PaTLR14 being significantly up-regulated. Furthermore, when spleen cells were treated with bacterial compositions, the majority of PaTLRs expression was up-regulated in response to Lipopolysaccharide (LPS) and lipophosphorylcholic acid (LTA) treatment, except for PaTLR21. Finally, changes in the expression levels of TLR-interacting genes were also observed under the stimulation of bacteria and bacterial compositions. The results of this study provide a preliminary reference for further understanding the mechanism of the innate immune response of the TLR gene family in silver pomfret and offer theoretical support for addressing the disease problems encountered during large-scale fish breeding.

Morphological and Molecular Functional Evidence of the Pharyngeal Sac in the Digestive Tract of Silver Pomfret, Pampus argenteus.

The pharyngeal sac is a comparatively rare organ in the digestive tract among teleost fishes. However, our understanding of this remarkable organ in the silver pomfret (Pampus argenteus) is limited. In the present study, we examined the various morphological and histological characteristics of the pharyngeal sac using histochemical techniques and electron microscopy. The pharyngeal sac showed unique characteristics such as well-developed muscular walls, weakly keratinized epithelium, numerous goblet cells, and needle-like processes on the papillae. The porous cavity of the papillae contained numerous adipocytes and was tightly enveloped by type I collagen fibers. These structures might provide mechanical protection and excellent biomechanical properties for grinding and shredding prey. A comparison of gene expression levels between the pharyngeal sac and esophagus using RNA-seq showed that phenotype-associated genes (epithelial genes and muscle genes) were upregulated, whereas genes related to nutrient digestion and absorption were downregulated in the pharyngeal sac. These results support the role of the pharyngeal sac in shredding and predigesting food. Overall, these findings provide a clearer understanding of the pharyngeal sac morphology and explain the morphological adaptations of the digestive tract for feeding on gelatinous prey. To our knowledge, this is the first report on pharyngeal sac gene expression in P. argenteus.

Dynamic Covalent Self-sorting in Molecular and Polymeric Architectures Enabled by Spiroborate Bond Exchange.

Self-sorting is commonly observed in complex reaction systems, which has been utilized to guide the formation of single major by-design molecules. However, most studies have been focused on non-covalent systems, and using self-sorting to achieve covalently bonded architectures is still relatively less explored. Herein, we first demonstrated the dynamic nature of spiroborate linkage and systematically studied the self-sorting behavior observed in the transformation between spiroborate-linked well-defined polymeric and molecular architectures, which is enabled by spiroborate bond exchange. The scrambling between a macrocycle and a 1D helical covalent polymer led to the formation of a molecular cage, whose structures are all unambiguously elucidated by single-crystal X-ray diffraction. The results indicate that the molecular cage is the thermodynamically favored product in this multi-component reaction system. This work represents the first example of a 1D polymeric architecture transforming into a shape-persistent molecular cage, driven by dynamic covalent self-sorting. This study will further guide the design of spiroborate-based materials and open the possibilities for the development of novel complex yet responsive dynamic covalent molecular or polymeric systems.

Cyanurate-Linked Covalent Organic Frameworks Enabled by Dynamic Nucleophilic Aromatic Substitution.

We report, for the first time, highly crystalline cyanurate-linked covalent organic frameworks synthesized via dynamic nucleophilic aromatic substitution. The high crystallinity is enabled by the bond exchange reaction (self-correction) between 2,4,6-triphenoxy-1,3,5-triazine and diphenols via reversible SNAr catalyzed by triazabicyclodecene. The CN-COFs contain flexible backbones that exhibit a unique AA'-stacking due to interlayer hydrogen bonding interactions. The isoreticular expansion study demonstrates the general applicability of this synthetic method. The resulting CN-COFs exhibited good stability, as well as high CO2/N2 selectivity.

Imparting Functionality and Enhanced Surface Area to a 2D Electrically Conductive MOF via Macrocyclic Linker.

The development of 2D electrically conductive metal-organic frameworks (EC-MOFs) has significantly expanded the scope of MOFs' applications into energy storage, electrocatalysis, and sensors. Despite growing interest in EC-MOFs, they often show low surface area and lack functionality due to the limited ligand motifs available. Herein we present a new EC-MOF using 2,3,8,9,14,15-hexahydroxyltribenzocyclyne (HHTC) linker and Cu nodes, featuring a large surface area. The MOF exhibits an electrical conductivity up to 3.02 × 10-3 S/cm and a surface area up to 1196 m2/g, unprecedentedly high for 2D EC-MOFs. We also demonstrate the utilization of alkyne functionality in the framework by postsynthetically hosting heterometal ions (e.g., Ni2+, Co2+). Additionally, we investigated particle size tunability, facilitating the study of size-property relationships. We believe that these results not only contribute to expanding the library of EC-MOFs but shed light on the new opportunities to explore electronic applications.