Improvement of secondary metabolite production with anti-inflammatory activity via adventitious roots culture of Aloe vera

Abstract

Aloe vera (Asphodeaceae) is a medicinal plant in which useful secondary metabolites are plentiful. Among the representative secondary metabolites of Aloe vera are the anthraquinones including aloe emodin and chrysophanol, which are tricyclic aromatic quinones synthesized via a plant-specific type III polyketide biosynthesis pathway. However, it is not yet clear which cellular responses can induce the pathway, leading to production of tricyclic aromatic quinones. In this study, I established optimized culture condition for Aloe vera adventitious roots culture. Then I examined the effect of endogenous elicitors on the type III polyketide biosynthesis pathway and identified the metabolic changes induced in elicitor-treated Aloe vera adventitious roots. The examination on culture condition revealed that MS solid media supplemented with 0.5 mg/L NAA was best condition to induce adventitious roots from leaf explants of Aloe vera. Optimal suspension culture condition for mass production of adventitious roots was observed in MS media with 0.3 mg/L IBA. Then, salicylic acid (SA), methyl jasmonate (MJ), and ethephon was treated to the adventitious roots as elicitors is capable of activating type III polyketide biosynthesis pathway. SA elicitation resulted in 10-11 and 5-13 folds increase in production of aloe emodin and chrysophanol compared to untreated control, respectively, suggesting that SA might activate the biosynthetic pathway for tricyclic aromatic quinones including aloe emodin and chrysophanol. Ultra-performance liquid chromatography-electrospray ionization mass spectrometry analysis identified a total of 37 SA-induced compounds, including aloe emodin and chrysophanol, and 3 of the compounds were tentatively identified as tricyclic aromatic quinones. Transcript accumulation analysis of polyketide synthase genes and gas chromatography mass spectrometry showed that these secondary metabolic changes resulted from increased expression of octaketide synthase genes and decreases in malonyl-CoA, which is the precursor for the tricyclic aromatic quinone biosynthesis pathway. In addition, anti-inflammatory activity was enhanced in extracts of SA-treated adventitious roots. The results suggest that SA has an important role in activation of the plant specific-type III polyketide biosynthetic pathway, and therefore that the efficacy of Aloe vera as medicinal agent can be improved through SA treatment.