Bamboo is a monocotyledonous plant in the grass family, which has been long regarded as both edible and medicinal. Ancient Chinese believe that bamboo leaves can remove “toxic heat” and have diuretic effects. Flavonoids constitute the major medicinal compoundsin bamboo leaves, but their biosynthesis and pharmacological mechanisms are poorly understood.

　　On March 6, 2020, Dr. Yong Wang's group at CAS Center for Excellence in Molecular Plant Science published a research paper entitled "Pathway-specific enzymes from bamboo and crop leaves biosynthesize anti-nociceptive C-glycosylated flavones" in Communications Biology. This study revealed the distribution and biosynthesis of C-glycosylated flavones (CGFs) in the grass family plants, achievedade novo synthesis of rare CGFs in microbial chassis, and also uncovered an unique anti-inflammatory and analgesicmechanism of isoorientin, one of the CGF compounds.

　　Wang and his colleagues first investigatedthe CGF spectrum in Gramineaeplants. They found that PACMAD clade (i.e, maize, foxtail millet) mainly produces C-monoglycosylated flavones, whereas BOP clade (i.e, rice, wheat) mainly gives rise to C-diglycosylated flavones. Through comparative genomic analysis, they identified 32 tandem duplicatedUGT708A family glycosyltransferases inthe co-linear regions of the genome of rice, Brachypodium, Moso bamboo, wheat, maize, sorghum and foxtail millet. Phylogenetic analysis further suggested that these UGT scan be divided into two branches, namely A and B. The glycosyltransferases of branch A strictly use UDP-glucose as substrate, while those of B branch is promiscuous to the sugar donor (recognizesboth UDP-glucose and UDP-arabinose).

　　Two unknown flavanone hydroxylases were subsequently isolated from Moso bamboo, and their biochemical functions were in vivo verified by integrating the naringenin precursor synthesizing-module and the glycosylation module into E. coli chassis cells.By using combinations of flavanone 2-hydroxylase (F2H) and flavone 3’-hydroxylase (F3’H) derived from different species, Wang and his colleaguessucceedin the de novobiosynthesis of four rare CGF compounds such as orientin, isoorientin, vitexin, and isovitexin in the E. coli system, with a yield from 20 to 30 mg/L.

　　Evaluation of the activity of the four majorCGF compoundsin bamboo leaves revealed that isoorientin exhibitedmost significant analgesic activity. The analgesic effect of phase I in formalin induced nociception was comparable to that of the positive control drugrotundine, and the analgesic effect of phase II was equivalent to that of the positive control aspirin. Further experiments found that isoorientin could inhibit the production of formalin-induced TNF-α, increase the production of the antihyperalgesic cytokine IL-10 in a dose-dependent manner, which indicated that isoorientin might targetTRPV1 and NR2B signaling pathways to achieve neuroprotective analgesia.

　　In summary, this study clarified the biosynthetic pathway of rare C-glycosylated flavones in grasses, evaluated the anti-inflammatory and analgesic effects of these glycosides, and revealed its possible pharmacological mechanism. It lays a foundation for further development of bioresources and utilization of rare active ingredients of grass plants.

　　This research was financially supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Strategic Priority Research Program of CAS and the National Key Laboratory of Plant Molecular Genetics, SIPPE, CAS.

　　Overview of this research. 

　　Upper panel: The proposed biosynthetic pathway of C-monoglucosylated flavone.

　　Lower panel: (left) A Phylogenetic tree of UGT708 enzymes; (right) Effects of isoorientin on the first and second phases of formalin-induced nociception in mice.

　　Link: https://www.nature.com/articles/s42003-020-0834-3 

　　Contact: 

　　Dr. Yong Wang, Professor

　　Key Laboratory of Synthetic Biology, CASCenter for Excellence in Molecular Plant Sciences/Shanghai Institute of Plant Physiology and Ecology (SIPPE), Chinese Academic of Sciences

　　Tel: 86-21-54924295

　　Email: yongwang@sibs.ac.cn