title: Precursor feeding studies and molecular characterization of geraniol synthase establish the limiting role of geraniol in monoterpene indole alkaloid biosynthesis in Catharanthus roseus leaves.
abstract: The monoterpene indole alkaloids (MIAs) are generally derived from strictosidine, which is formed by condensation of the terpene moiety secologanin and the indole moiety tryptamine. There are conflicting reports on the limitation of either terpene or indole moiety in the production of MIAs in Catharanthus roseus cell cultures. Formation of geraniol by geraniol synthase (GES) is the first step in secologanin biosynthesis. In this study, feeding of C. roseus leaves with geraniol, but not tryptophan (precursor for tryptamine), increased the accumulation of the MIAs catharanthine and vindoline, indicating the limitation of geraniol in MIA biosynthesis. This was further validated by molecular and in planta characterization of C. roseus GES (CrGES). CrGES transcripts exhibited leaf and shoot specific expression and were induced by methyl jasmonate. Virus-induced gene silencing (VIGS) of CrGES significantly reduced the MIA content, which was restored to near-WT levels upon geraniol feeding. Moreover, over-expression of CrGES in C. roseus leaves increased MIA content. Further, CrGES exhibited correlation with MIA levels in leaves of different C. roseus cultivars and has significantly lower expression relative to other pathway genes. These results demonstrated that the transcriptional regulation of CrGES and thus, the in planta geraniol availability plays crucial role in MIA biosynthesis.
authors.affiliation: CSIR-Central Institute of Medicinal and Aromatic Plants Research Centre, Bengaluru 560065, India; Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Krishna
authors.initials: K
authors.lastname: Kumar
authors.affiliation: CSIR-Central Institute of Medicinal and Aromatic Plants Research Centre, Bengaluru 560065, India; Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Sarma Rajeev
authors.initials: SR
authors.lastname: Kumar
authors.affiliation: CSIR-Central Institute of Medicinal and Aromatic Plants Research Centre, Bengaluru 560065, India; Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Varun
authors.initials: V
authors.lastname: Dwivedi
authors.affiliation: CSIR-Central Institute of Medicinal and Aromatic Plants Research Centre, Bengaluru 560065, India; Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Avanish
authors.initials: A
authors.lastname: Rai
authors.affiliation: Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Ashutosh K
authors.initials: AK
authors.lastname: Shukla
authors.affiliation: Analytical Chemistry Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India.
authors.forename: Karuna
authors.initials: K
authors.lastname: Shanker
authors.affiliation: CSIR-Central Institute of Medicinal and Aromatic Plants Research Centre, Bengaluru 560065, India; Biotechnology Division, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Lucknow 226015, India. Electronic address: da.nagegowda@cimap.res.in.
authors.forename: Dinesh A
authors.initials: DA
authors.lastname: Nagegowda
mesh_terms: D000080462:Acyclic Monoterpenes; D030008:Catharanthus / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D046948:Secologanin Tryptamine Alkaloids / Q000378:metabolism*; D013729:Terpenes / Q000378:metabolism*
chemical_list: D000080462:Acyclic Monoterpenes; D010940:Plant Proteins; D046948:Secologanin Tryptamine Alkaloids; D013729:Terpenes; C007836:geraniol
keywords: Catharanthus roseus; Gene expression; Geraniol; Geraniol synthase; Monoterpene indole alkaloids; Virus-induced gene silencing