Geissoschizine synthase controls flux in the formation of monoterpenoid indole alkaloids in a Catharanthus roseus mutant

• Published in: Planta 2018-03, Vol.247 (3), p.625-634
• Main Authors: Qu, Yang, Thamm, Antje M. K., Czerwinski, Matthew, Masada, Sayaka, Kim, Kyung Hee, Jones, Graham, Liang, Ping, De Luca, Vincenzo
• Format: Article
• Language: English
• Subjects: Aglycones; Agriculture; Ajmalicine; Alkaloids; Antihypertensives; Antineoplastic drugs; beta-Glucosidase - metabolism; Biochemistry; Biomedical and Life Sciences; Biosynthesis; Carbolines - metabolism; Catharanthus - enzymology; Catharanthus - genetics; Catharanthus - metabolism; Catharanthus roseus; Ecology; Enzymatic activity; Enzymes; Forestry; Gene silencing; Glucosidase; Glucosidases - metabolism; Indoles; Life Sciences; Multienzyme Complexes - metabolism; Mutants; Mutation - genetics; ORIGINAL ARTICLE; Plant Proteins - metabolism; Plant Sciences; Plants (botany); Secologanin Tryptamine Alkaloids - metabolism; Thin layer chromatography; Vinblastine; Vinblastine - analogs & derivatives; Vinblastine - metabolism; Vincristine; Vindoline; Viruses
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-017-2812-7

The Madagascar periwinkle [Catharanthus roseus (L.) G. Don] is a commercially important horticultural flower species and is a valuable source for several monoterpenoid indole alkaloids (MIAs), such as the powerful antihypertensive drug ajmalicine and the antineoplastic agents, vinblastine and vincristine. While biosynthesis of the common MIA precursor strictosidine and its reactive aglycones has been elucidated, the branch point steps leading to the formation of different classes of MIAs remain poorly characterized. Screening of 3600 ethyl methyl sulfonate mutagenized C. roseus plants using a simple thin-layer chromatography screen yielded a mutant (M2-0754) accumulating high levels of ajmalicine together with significantly lower levels of catharanthine and vindoline. Comparative bioinformatic analyses, virus-induced gene silencing, and biochemical characterization identified geissoschizine synthase, the gateway enzyme that controls flux for the formation of iboga and aspidosperma MIAs. The reduction of geissoschizine synthase transcripts in this high ajmalicine mutant, together with increased transcripts and enzyme activities of strictosidine β-glucosidase and of heteroyohimbine synthase, explains the preferential formation of ajmalicine in the mutant instead of catharanthine and vindoline that accumulates in the wild-type parent. Reciprocal crosses established that that the high ajmalicine phenotype is inherited as a Mendelian recessive trait.