Effect of endophytic fungi on the host plant growth, expression of expansin gene and flavonoid content in Tetrastigma hemsleyanum Diels & Gilg ex Diels

BACKGROUND AND AIMS: Tetrastigma hemsleyanum is a rare medicinal plant in China. Because it requires very strict environmental conditions to grow, it usually takes 3–5 years to form calabash-shaped roots and is difficult to meet the demand of Chinese medical market. Although it is known that endophytes can enhance the growth of the host plants, the molecular mechanism of the interplay between endophytes and their host plants growth is not completely understood yet. The aim of this study was to determine if endophytes can reduce the growth cycle and promote the medicinal ingredients in Tetrastigma hemsleyanum, and elucidate its underlying molecular mechanism. METHODS: Endophytic fungi were isolated and identified from the calabash-shaped root of Tetrastigma hemsleyanum. The fermentation broth of 6 endophyte strains (named as TH09, TH12, TH14, TH15, TH17 and TH26) were added to the MS medium to culture axenic plantlets. After 30 days of culture, the net growth, expansin gene expression and the flavonoid content were measured. RESULTS: From the calabash-shaped roots, we isolated 31 endophytic fungi belonging to 10 genera: Fusarium, Rhizopycnis, Colletotrichum, Cylindrocarpon, Emericellopsi, Penicillium, Plectosphaerella, Aspergillus tubingensis, Alternaria and Sarocladium, of which Fusarium is the dominant genus. Addition of the fermentation broth from strains TH12, TH15 and TH26 significantly increased the plant growth. Strains TH15 and TH26’s fermentation broth increased the expression of Th-exp (an expansin gene), while addition of the fermentation broth from TH14 increased Th-exp expression in leaves and stems, but decreased Th-exp expression in the root. Flavonoid content was increased in the presence of fermentation broth from strains TH09, TH14, TH17 and TH26. Particularly, the fermentation broth from TH26 can promote plant growth, enhance Th-exp expression and increase the flavonoid content in Tetrastigma hemsleyanum. CONCLUSIONS: The results demonstrated that endophytic fungi from the calabash-shaped root of Tetrastigma hemsleyanum can regulate plant growth, expression of expansin gene and flavonoid content.