The effect of rhizosphere soil on the flavonoid metabolism in the roots of Tetrastigma hemsleyanum

Background: Tetrastigma hemsleyanum (T. hemsleyanum) is a precious and rare traditional Chinese medicinal plant. Flavonoid is its main medicinal ingredient. Wild T. hemsleyanum (W-TH) growing in Zhejiang Province, China is recognized as a medicinal material of “San Ye Qing” Dao-di herbs. The different origins and thus the contents of medicinal ingredients are the key criteria used to determine whether the medicinal materials are authentic Dao-di herbs. However, it is less known how the eco-environments of its specific producing area, especially microbial community in rhizosphere soil, affect the content of medicinal ingredients in “San Ye Qing”. In the present study, we determined the content of total flavonoids and the enzymatic activity of phenylalanine ammonia-lyase (PAL) in the roots of W-TH and artificially cultivated T. hemsleyanum (C-TH), as well as the nutrient compositions and metagenome in rhizosphere soil. The effects of the rhizosphere soil on the flavonoid metabolism in T. hemsleyanum were evaluated. Results: The contents of total flavonoids and the PAL activity were higher in W-TH root than in C-TH root. The contents of both available phosphorus and available potassium were higher in the rhizosphere soil of W-TH than in that of C-TH, while the contents of nitrogen and organic matter in the rhizosphere root of C-TH were higher than that of W-TH. Compared with the rhizosphere of C-TH, the abundances of genera Enterobacter, Serratia, Raoultella, Kluyvera, Comamonas, Acinetobacte, and Arthrobacter, and the pathways related to nitrogen metabolism, inositol phosphate metabolism, phosphinate metabolism, and phosphotransferase system in the rhizosphere of W-TH were significantly different. There existed differences in phenylpropanoid biosynthesis and phenylalanine metabolism in the rhizospheres of W-TH and C-TH. Conclusions: The contents of nitrogen and available phosphorus in the rhizosphere soil affect diversity abundance, nitrogen metabolism, phosphorus metabolism, and phenylalanine (Phe) anabolism of rhizosphere microorganisms. They may further affect Phe content and PAL activity for the synthesis of flavonoids in the root of T. hemsleyanum.