The antifungal mechanism of the biogenic antimicrobial Ningnanmycin on Didymella segeticola involves binding to tryptophanyl-tRNA synthetase, inhibiting translation

Abstract BackgroundTea [Camellia sinensis (L.) Kuntze] has been recently cultivated in Guizhou Province, China, where the cultivated area has reached 350,000 hectares, making it the major tea-growing region in world. Tea leaf spot caused by Didymella segeticola can induce the decreases in quality and quantity of tea leaves, which is an important disease in tea plantations at higher altitude, where cold spells occur in late spring. As a promising biogenic antimicrobial agent against crop diseases, Ningnanmycin (NNM) was produced from Streptomyces noursei var. xichangensisn, represented higher field efficiency against fungal, bacterial and viral phytopathogens, lower toxicity and lower residue. However, the action mechanism of NNM against phytopathogens just stays on the stage of anti-viral mechanism, which limits the application of NNM in the management of plant fungal diseases. Here, we studied the action mechanism of NNM against D. segeticola using many methods of transcriptome, ultrastructure, molecular biology and molecular docking.ResultsNNM strongly inhibited the mycelial growth of D. segeticola with the half-maximal effective concentration of 1287.54 U/mL. Optical, fluorescence, scanning and transmission electron microscopy were applied to observe morphological changes of cellular, organelle for D. segeticola treated by NNM. A great number of morphological changes of D. segeticola indicated that NNM could affect the biosynthesis of the phytopathogen. For further, RNA-Seq results showed that NNM treated D. segeticola induced 1,363 significantly differentially expressed genes (DEGs) comparing with the control (P < 0.05). The DEGs were highly enriched in structural component of ribosome, ribosome and translation by Gene Ontology, as well as in ribosome pathway at Kyoto Encyclopedia of Genes and Genomes. NNM regulated the mRNA levels of RPS7, RPS9, RPS10b, RPL9, RPL11 and TrpRS, and represent the different regulation mode by the comparative analysis with a classical translation extension inhibitor, cycloheximide. The molecular docking indicated that NNM possessed a marked affinity with TrpRS, with the binding free energy is -101.55 kcal/mol.ConclusionsNNM could potentially affect translation by binding to tryptophanyl-tRNA synthetase, thus inhibiting mycelial growth. This study will provide insights for anti-fungal mechanism of NNM and contribute to the control and prevention of tea leaf spot disease.