Octylamine regulating the mechanical robustness of natural rubber by involving in the construction of crosslinking network.

The formation of three dimensional network structure is critical in determining mechanical properties of natural rubber (NR). Consequently, it is vital to regulate crosslinking network of NR by controlling vulcanization process. Inspired by our previous studies on contribution of non-rubber components (NRCs) to the excellent properties of NR, we find octylamine in NRCs decreases the activation energy (Ea) of vulcanization from 82.73 kJ/mol to 44.34 kJ/mol, thereby reducing vulcanization time from 18.67 min to 2.71 min. From microscopic perspective, octylamine tends to coordinate with zinc ions to improve dispersion of ZnO in NR. And octylamine promotes ring-opening reaction of S8 to favor formation of polysulfide intermediates. Therefore, the incorporation of octylamine remarkably improves vulcanization efficiency, which contributes to the formation of a more homogeneous network with higher crosslinking density, enhancing remarkably the strength and toughness of NR. As a result, the tensile strength and fracture energy of samples are as high as 31.15 MPa and 68.88 kJ/m2, respectively. In addition, even with a 60 % reduction in ZnO content, the NR samples still maintain high vulcanization efficiency and excellent mechanical properties after the addition of octylamine, which provides a green and feasible way to alleviate the environmental pollution caused by ZnO.

Discovery and Biochemical Characterization of N-methyltransferase Genes Involved in Purine Alkaloid Biosynthetic Pathway of Camellia gymnogyna Hung T.Chang (Theaceae) from Dayao Mountain.

In the present study, purine alkaloid analysis and transcriptome of Camellia gymnogyna Hung T. Chang (Theaceae) from Dayao Mountain were performed by high-performance liquid chromatography (HPLC) and RNA-Seq, respectively. The results showed that the major purine alkaloids accumulated in Camellia gymnogyna Hung T. Chang (Theaceae) were theobromine together with a small amount of theacrine and caffeine. Through polymerase chain reaction (PCR), three types of cDNA encoding N-methyltransferases were isolated from the leaves of Camellia gymnogyna Hung T. Chang (Theaceae) and designated GCS1, GCS2, and GCS3. We subsequently expressed GCS1, GCS2, and GCS3 in Escherichia coli and incubated lysates of the bacterial cells with a variety of xanthine substrates in the presence of S-adenosyl-L-methionine as the methyl donor. We found that the recombinant GCS1 proteins catalyzed 1,3,7-trimethyluric acid to produce theacrine, the recombinant GCS3 proteins catalyzed 7-methylxanthine to produce theobromine, while the recombinant GCS2 proteins did not catalyze any xanthine derivatives. Simultaneous analysis of the expressions of GCS1, GCS2, GCS3, and a caffeine synthase gene (TCS1) in Camellia gymnogyna Hung T. Chang (Theaceae) and other tea plants provided a reference for further research on the functions of these genes.

N-Methyltransferases of Caffeine Biosynthetic Pathway in Plants.

Caffeine (Cf) is one of the important components of plant-derived drinks, such as tea, coffee, and cola. It can protect soft tissues from being infected by pathogens and is also medically beneficial for human health. In this review, we first introduced the Cf biosynthesis pathways in plants and the related N-methyltransferases (NMTs), with a focus on the current research status of the substrate specificity, structural basis for substrate recognition, and catalytic mechanism in members of the caffeine synthase gene family. In addition, we addressed the expression characteristics and potential regulatory mechanisms of NMTs and also projected the future research directions. The goal was to summarize the Cf biosynthetic pathway and related NMTs in plants and to provide the molecular basis for regulating the caffeine biosynthesis, so as to effectively guide future tea and coffee breeding.