A MDR transporter contributes to the different extracellular production of sesquiterpene pyridine alkaloids between adventitious root and hairy root liquid cultures of Tripterygium wilfordii Hook.f.
TwMDR1 transports sesquiterpene pyridine alkaloids, wilforine and wilforgine, into the hairy roots of T. wilfordii Hook.f. resulting in low secretion ratio of alkaloids.
Hairy roots (HRs) exhibit high growth rate and biochemical and genetic stability. However, varying secondary metabolites in HR liquid cultures mainly remain in root tissues, and this condition may affect cell growth and cause inconvenience in downstream extraction. Studies pay less attention to adventitious root (AR) liquid cultures though release ratio of some metabolites in AR liquid cultures is significantly higher than that of HR. In Tripterygium wilfordii Hook.f., release ratio of wilforine in AR liquid cultures reached 92.75 and 13.32% in HR on day 15 of culture. To explore potential roles of transporters in this phenomenon, we cloned and functionally identified a multidrug resistance (MDR) transporter, TwMDR1, which shows high expression levels in HRs and is correlated to transmembrane transportation of alkaloids. Nicotiana tabacum cells with overexpressed TwMDR1 efficiently transported wilforine and wilforgine in an inward direction. To further prove the feasibility of genetically engineered TwMDR1 and improve alkaloid production, we performed a transient RNAi experiment on TwMDR1 in T. wilfordii Hook.f. suspension cells. Results indicated that release ratios of wilforine and wilforgine increased by 1.94- and 1.64-folds compared with that of the control group, respectively. This study provides bases for future studies that aim at increasing secretion ratios of alkaloids in root liquid cultures in vitro.
KeywordsABC transporter Hairy root Adventitious root Sesquiterpene pyridine alkaloids
This study was supported by Educational Commission of Anhui Province of China (KJ2016A668), the National Natural Science Foundation of Anhui Province (1708085QC52), the National Natural Science Foundation of China (Grant No. 31272110) and the Key Project of the Outstanding Young Talent Support Program of the University of Anhui Province (gxyqZD2016264).
XZ and CZ: conceived and designed the experiments. GM and JH: performed the experiments. JZ: analyzed the data. XZ and CZ: wrote the paper.
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interest.
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