Rutaceae plants are known for being a rich source of coumarins. Preliminary molecular docking showed that there was no significant difference for coumarins in Clausena and Murraya, both of which had high scoring values and showed good potential inhibitory activity to the MAO-B enzyme. Overall, 32 coumarins were isolated from Murraya exotica L., including a new coumarin 5-demethoxy-10′-ethoxyexotimarin F (1). Their structures were elucidated on the basis of a comprehensive analysis of 1D and 2D NMR and HRMS spectroscopic data, and the absolute configurations were assigned via a comparison of the specific rotations and the ECD exciton coupling method. The potential of new coumarin (1) as a selective inhibitor of MAO-B was initially evaluated through molecular docking and pharmacophore studies. Compound (1) showed selectivity for the MAO-B isoenzyme and inhibitory activity in the sub-micromolar range with an IC₅₀ value of 153.25 ± 1.58 nM (MAO-B selectivity index > 172).

Anthracnose is a major disease of walnut, which seriously reduces the yield and quality of walnut in Yunnan province. Therefore, it is necessary to explore and find a biological control agent for the prevention and control of anthracnose disease. In this study, an endophytic Bacillus WB1, with broad-spectrum antibacterial activity was isolated and screened from healthy walnut roots. The strain WB1 was identified as Bacillus siamensis WB1 based on morphological characteristics, physiological and biochemical tests, and 16S rRNA gene sequence analysis. Bacillus siamensis WB1 produces siderophores and indole-3-acetic acid and solubilizes inorganic phosphate. The strain WB1 not only showed a significant inhibition effect on fourteen phytopathogens, but also showed obvious inhibition on the spore germination of Colletotrichum acutatum. Meanwhile, strain WB1 can code genes for the production of antifungal lipopeptides and generate extracellular hydrolytic enzymes (protease, β-1, 3-glucanase, cellulase, and amylase). In addition, WB1 activated the systemic resistance of the host plant by enhancing the activity of defense enzymes, including phenylalanine ammonia lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO). The results of greenhouse assays also revealed that B. siamensis WB1 can effectively reduce the occurrence and severity of walnut anthracnose disease. These results also indicated that B. siamensis WB1 is a potential biocontrol agent for walnut anthracnose.

Salt and low temperature are serious abiotic stresses and important constraints to agricultural productivity across the globe. These abiotic stresses negatively affect plant growth and physiological, biochemical, and molecular processes. Glycine betaine (GB) is an important osmoprotectant that enables plants to resist salinity, low temperature, and drought. GB can be synthesized in many organisms, including animals, plants, and bacteria. In higher plants, GB is synthesized through two-step oxidation of choline. However, rice, an important food crop, cannot synthesize GB. Thus, conferring the ability to synthesize GB to rice through genetic engineering is of great significance for enhancing its tolerance to abiotic stress. Recently, an enzyme, GSDMT (glycine, sarcosine, and dimethylglycine methyltransferase) was found in a diatom, Talassiosira pseudonana, and found able to catalyze the three successive methylation steps of glycine to form GB. This biosynthetic pathway for GB synthesis is also the simplest in living organisms. Here, the optimized codon of the TpGSDMT gene sequence was synthesized and cloned into an overexpression vector, pBWA(V)HS, which contains a CaMV 35S promoter, and then, the constructed vector was transferred into rice (Oryza sativa L. ssp. Japonica). The GB content in transgenic rice showing overexpression of TpGSDMT was significantly increased, and these transformants exhibited markedly enhanced tolerance to salt and low temperature. These results indicate that the TpGSDMT gene can be used for the genetic improvement in crop plants’ resistance to salinity and low temperature.

Phosphoethanolamine N-methyltransferase (PEAMT) is a key enzyme that catalyzes three successive methylation steps of phosphoethanolamine (P-EA) to phosphocholine (P-Cho). Meanwhile, P-Cho is a major precursor of phosphatidylcholine (PC) and glycine betaine (GB), which are involved in cell signal transduction, stress response, etc. Therefore, the PEAMT gene plays an essential role in plant growth and development as well as stress resistance. There are two homologous PEAMT genes in rice (Oryza sativa L. ssp. japonica), namely, OsPEAMT1 and OsPEAMT2. However, there has not been any comprehensive functional analysis of these two genes. Here, we employed bioinformatics methods to analyze the amino acid sequences and promoters of OsPEAMT1 and OsPEAMT2, and found that both proteins contain two methyltransferase domains. OsPEAMT1 is highly similar with ZmPEAMT, and OsPEAMT2 is closely related to LmPEAMT and TaPEAMT. There are abundant plant hormone response elements, stress response elements and low-temperature response elements in the promoters of OsPEAMT1 and OsPEAMT2. The in vitro enzymatic activity assays of recombinant proteins of OsPEAMT1 and OsPEAMT2 indicated that they can catalyze the production of P-Cho from P-EA, respectively. Meanwhile, the endogenous P-Cho content increased significantly (p < 0.05) when exogenous P-EA was added to rice. These indicate that OsPEAMT1 and OsPEAMT2 proteins have catalytic functions in vivo and in vitro. The expression patterns of both genes are different in different tissues, flowers and seeds at various developmental stages. Additionally, both genes have different responses to salt and low-temperature stress. This study supplies valuable insights into the function of OsPEAMT1 and OsPEAMT2, and it will provide key targets for rice molecular breeding, offering important insights for the development of rice with stress resistance and high yield.