In vivo and in vitro antifungal activities of five alkaloid compounds isolated from Picrasma quassioides (D. Don) Benn against plant pathogenic fungi

Synthesis and Antifungal Activities of Novel Griseofulvin Derivatives as Potential Anti-Phytopathogenic Fungi Agents

The extensive and repeated application of chemical fungicides results in the rapid development of fungicide resistance. Novel antifungal pesticides are urgently required. Natural products have been considered precious sources of pesticides. It is necessary to discover antifungal pesticides by using natural products. Herein, 42 various griseofulvin derivatives were synthesized. Their antifungal activities were evaluated in vitro. Most of them showed good antifungal activity, especially 3d exhibited a very broad antifungal spectrum and the most significant activities against 7 phytopathogenic fungi. In vivo activity results suggested that 3d protected apples and tomatoes from serious infection by phytopathogenic fungi. These proved that 3d had the potential to be a natural product-derived antiphytopathogenic fungi agent. Furthermore, docking analysis suggested that tubulin might be one of the action sites of 3d. It is reasonable to believe that griseofulvin derivatives are worth further development for the discovery of new pesticides.

Streptothricin-F Inhibition of FtsZ Function: A Promising Approach for Controlling Pseudomonas syringae pv. actinidiae

Pseudomonas syringae pv. actinidiae (Psa) is a significant pathogenic bacterium affecting the kiwifruit industry. This study investigated the target sites of streptothricin-F (ST-F), produced by Streptomyces lavendulae gCLA4. The inhibition of ST-F on Psa was examined by the microscopic structural differences of Psa before and after treatment with ST-F, as well as the interaction between ST-F and cell division-related proteins. The results revealed filamentation of Psa after ST-F treatment, and fluorescence microscopy showed that ST-F inhibited the formation of the Z-ring composed of FtsZ protein. In vitro experiments and molecular docking demonstrated that ST-F can bind to FtsZ with a binding energy of 0.4 μM and inhibit FtsZ's GTP-dependent polymerization reaction. In addition, ST-F does not exert inhibitory effects on cell division in Psa strains overexpressing ftsZ. In conclusion, FtsZ is one of the target sites for ST-F inhibition of Psa, highlighting its potential as a therapeutic target for controlling Psa-induced kiwifruit bacterial canker.

Design, Synthesis, Structure-Activity Relationship, and Three-Dimensional Quantitative Structure-Activity Relationship of Fusarium Acid Derivatives and Analogues as Potential Fungicides

In research related to fungicides, the development of compounds from natural products with high antifungal activity has attracted considerable attention. Fusaric acid (FA), an alkaloid isolated from the metabolites of Fusarium oxysporum, is an important precursor for developing pharmacologically active herbicides. In our previous work, we reported that FA has a wide range of inhibitory activities against 14 plant pathogenic fungi. In particular, it exhibited excellent antifugal effects on Colletotrichum higginsianum (EC50 = 31.7 μg/mL). Herein, to explore the practical application in the agricultural field, the design and synthesis of three series of FA derivatives and their inhibitory activities against plant pathogenic fungi were examined. Results demonstrated that the optimized FA derivatives had excellent inhibitory activities against C. higginsianum, Helminthosporium (Harpophora maydis), and Pyricularia grisea. In particular, the inhibitory activities were considerably improved when the 5-butyl groups of FA were substituted. The EC50 of C. higginsianum and P. grisea was only 1.2 and 12.0 μg/mL when 5-butylalkyl groups were substituted with 5-([1,1'-biphenyl]-4-yl) and 5-phenyl, respectively. Moreover, the safety index of target compounds, which was obtained from the treatment index of medicines, on rice seeds was evaluated. Finally, 16 leading compounds (H4, H22-H24, H27, H29, H30-H34, H37, H45, H50, H52, and H53) were obtained; they had considerable potential for additional modification and optimization as agricultural fungicides. Moreover, three-dimensional quantitative structure-activity relationship models were developed for obtaining a systematic structure-activity relationship profile to explore the possibility of more potent FA derivatives as novel fungicides.

Natural product osthole can significantly disrupt cell wall integrity and dynamic balance of Fusarium oxysporum

Dendrobium officinale Kimura et Migo is a traditional Chinese herbal medicinal plant. However, the frequent occurrence of soft rot disease (SRD) is one of the most harmful diseases in D. officinale production in recent years, which can seriously affect its yield and quality. In this study, the major pathogenic fungus (SR-1) was isolated from D. officinale with typical symptoms of SRD, and was identified as Fusarium oxysporum through morphological and molecular identification. The biological activities of five natural products were determined against F. oxysporum using a mycelial growth inhibition assay. The results showed that osthole had the highest antifungal activity against F. oxysporum, with an EC50 value of 6.40 mg/L. Scanning electron microscopy (SEM) showed that osthole caused F. oxysporum mycelia to shrink and deform. Transmission electron microscopy (TEM) showed that the organelles were blurred and the cell wall was thickened in the presence of osthole. The sensitivity of F. oxysporum to calcofluor white (CFW) staining was significantly enhanced by osthole. Relative conductivity measurements and propidium iodide (PI) observation revealed that osthole had no significant effect on the cell membrane. Further experiments showed that the activity of chitinase and β-1,3-glucanase were decreased, and expression levels of chitinase and β-1,3-glucanase related genes were significantly down-regulated after treatment with osthole. In conclusion, osthole disrupted the cell wall integrity and dynamic balance of F. oxysporum, thereby inhibiting normal mycelial growth.