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Plant-derived monoterpene indole alkaloids (MIAs) from Uncaria rhynchophylla (UR) have huge medicinal properties in treating Alzheimer's disease, Parkinson's disease, and depression. Although many bioactive UR-MIA products have been isolated as drugs, their biosynthetic pathway remains largely unexplored. In this study, untargeted metabolome identified 79 MIA features in UR tissues (leaf, branch stem, hook stem, and stem), of which 30 MIAs were differentially accumulated among different tissues. Short time series expression analysis captured 58 pathway genes and 12 hub regulators responsible for UR-MIA biosynthesis and regulation, which were strong links with main UR-MIA features. Coexpression networks further pointed to two strictosidine synthases (UrSTR1/5) that were coregulated with multiple MIA-related genes and highly correlated with UR-MIA features (r > 0.7, P < 0.005). Both UrSTR1/5 catalyzed the formation of strictosidine with tryptamine and secologanin as substrates, highlighting the importance of key residues (UrSTR1 : Glu309, Tyr155; UrSTR5 : Glu295, Tyr141). Further, overexpression of UrSTR1/5 in UR hairy roots constitutively increased the biosynthesis of bioactive UR-MIAs (rhynchophylline, isorhynchophylline, corynoxeine, etc), whereas RNAi of UrSTR1/5 significantly decreased UR-MIA biosynthesis. Collectively, our work not only provides candidates for reconstituting the biosynthesis of bioactive UR-MIAs in heterologous hosts but also highlights a powerful strategy for mining natural product biosynthesis in medicinal plants. [ABSTRACT FROM AUTHOR]

Abstract: We report the effects of hydrogen sulfide (H2S) on flower senescence in various species of cut flowers. H2S was found to delay flower opening and senescence in cut flowers and branches from Erigeron annuus (L.), Euonymus maackii Rupr., Hibiscus syriacus L., Liriope spicata (Thump.), Loropetalum chinense (R. Br.), Punica granatum L., Rosa chinensis Jacq., and Salix matsudana Koidz. Cut explants of these plants were cultured in solution containing different concentrations of the H2S donor, NaHS. H2S donor treatment prolonged the vase time of cut flowers and prevented senescence in a dose-dependent manner. We measured the levels of malondialdehyde (MDA) as an indicator of oxidative damage to cells and showed that it was inversely related to endogenous H2S concentration in explants. Flowers that had senesced showed higher levels of MDA and lower amounts of H2S. Furthermore, NaHS treatment increased the activities of catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (POD), and sustained much lower levels of H2O2 and O2 − in cut flowers of E. annuus and explant leaves of S. matsudana. The present study implies that H2S is involved in improving longevity of cut flowers and functions in activity of antioxidant enzymes in plants. [Copyright &y& Elsevier]