A fungal endophyte of the medicinal plant, Alisma orientale, promotes plant growth and bioactive compound accumulation

Introduction The Asian water plantain, Alisma orientale (Sam.) Juzep, is a flowering hydrophytic plant that grows in marshes. In traditional Chinese medicine, the rhizome of A. orientale is highly valued for its medicinal properties. Endophytic microbes modulate plant growth and the biosynthesis of secondary metabolites, however little is known concerning these effects in A. orientale . Methods Here, high-throughput sequencing and culturing methods were utilized to investigate the endophytic fungal diversity in the rhizomes, flowers, roots and leaves of A. orientale . In vitro assays were employed to screen for strains exhibiting high growth-promoting abilities based on phosphate solubilization, siderophore production, oxidative stress resistance, and indole-3-acetic acid (IAA) production. Transcriptomics and whole genome sequencing were employed to investigate the underlying molecular mechanisms. Results These data revealed that the Ascomycota and Basidiomycota were dominant phyla in all parts, with significant variation in fungal community composition observed at the genus level, as reflected in alpha and beta diversity indices. A total of 19 different endophytic fungal strains were isolated via culturing methods from the four different parts of A. orientale . In vitro assays resulted in the identification of four isolates subsequently used for co-culturing with sterile A. orientale to monitor plant-growth and terpenoid production. These latter results identified one promising strain, RT1, characterized as Pseudothielavia terricola . Isolate RT1 enhanced plant growth by 100–121% with respect to root length and plant height as compared to controls. After 21 days of treatment with strain RT1, the contents of the triterpenoids alisols B-23, C-23, and B were 4.5–5.5 times higher than those of the controls. Transcriptomics revealed enhanced expression of key enzymes involved in plant growth and bioactive compound accumulation, including 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), mevalonate diphosphate decarboxylase (MVD), farnesyl diphosphate synthase (FPPS), 1-deoxy- D -xylulose-5-phosphate reductoisomerase (DXR), 1-deoxy- D -xylulose-5-phosphate synthase (DXS), farnesyl-diphosphate farnesyltransferase (FDFT1), and squalene monooxygenase (SQLE) during RT1 interaction. Whole genome sequencing of P. terricola revealed the presence of several gene clusters involved in tryptophan synthesis. Discussion This study establishes endophytic fungal enhancement of A. orientale growth and bioactive compound accumulation, thereby increasing crop value and utility.