Mechanism of alkaloid synthesis in Isatis indigotica infected by Plasmodiophora brassicae

Abstract

To explore expression level of alkaloid and its key synthetase gene in Isatis indigotica upon Plasmodiophora brassicae exposure. The grades of disease severity according to morphology were verified. Moreover, histological observation, physiological and biochemical parameters have been collected together with transcriptomic and metabolomic analysis in Isatis indigotica after infection for 0, 7, 14, 21 d. The results were as follows: (1) After inoculation for 0, 7, 14, 21 d with Plasmodiophora brassicae, Isatis indigotica showed club root grades in 0, 1, 3, and 5 respectively, notably, cortical invasion occurred on 7 d. (2) When Plasmodiophora brassicae exposed lasting 14 d later, the contents of soluble protein and malondialdehyde, along with superoxide dismutase, peroxidase, polyphenol oxidase and catalase activities in Isatis indigotica increased significantly compared to control group at time depended manner. (3) A total of 161 alkaloids were detected in metabolomics, among those alkaloids, indoles were noticed as the most abundant form. There were 16, 17 and 39 discriminating metabolites had been spotted after infected with Plasmodiophora brassicae for 7, 14, 21 d, the most discriminating metabolites enriched at alkaloid and amino acid metabolism pathways. (4) Transcriptome analysis showed that there were 2 439, 256 and 6 437 genes expression alteration for 7, 14, 21 d compared to control, those differentially expressed genes enriched at 11 alkaloids related metabolism pathways. Markedly, expression level of 9 genes (encoding for enzymes thebaine synthase, tyrosine aminotransferase, indole-3-pyruvate monooxygenase and aldehyde dehydrogenase) were increased after infection for 7, 14, 21 d. The results reveal the interaction between Plasmodiophora brassicae and Isatis indigotica, explored the effects of Plasmodiophora brassicae on indole alkaloid synthesis and its key enzyme genes, and lay a foundation for later research on resistance genes and alkaloid secondary metabolic pathways in Isatis indigotica.

Keywords

• isatidis radix
• plasmodiophora brassicae
• antioxidant enzymes
• functional gene
• indole alkaloid
• metabolome