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    Biosynthesis of Carotenoid-Derived Plant Signaling Molecules

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    PhD Dissertation Final_Lina Baz.pdf
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    PhD Dissertation Final_Lina Baz
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    Type
    Dissertation
    Authors
    Baz, Lina cc
    Advisors
    Al-Babili, Salim cc
    Committee members
    Arold, Stefan T. cc
    Tester, Mark A. cc
    Zurbriggen, Mmatias
    Program
    Bioscience
    KAUST Department
    Biological and Environmental Sciences and Engineering (BESE) Division
    Date
    2018-10
    Permanent link to this record
    http://hdl.handle.net/10754/630105
    
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    Abstract
    Carotenoids are precursors of hormones and signaling molecules across all kingdoms of life. An increasing body of evidence suggests the presence of yet unidentified carotenoid-derived metabolites (apocarotenoids) with developmental and regulatory functions, besides the known plant hormones abscisic acid (ABA) and strigolactones (SLs). Generally, apocarotenoid synthesis is initiated by carotenoid cleavage dioxygenases (CCDs), which constitute a ubiquitous family of non-heme iron enzymes. In SL biosynthesis, an iron-binding cis/trans-isomerase, DWARF 27 (D27) converts all-trans-β-carotene into 9-cis-β-carotene. This reaction is followed by a double bond cleavage at 9, 10 position, mediated by the stereospecific CCD7. The cis-configured cleavage product of CCD7, 9-cis-β-apo-10’-carotenal, is simultaneously cleaved, triple-oxygenated and rearranged by CCD8, to produce carlactone (CL). CL is a central metabolite and the precursor of a wide range of SLs. The aim of this work is to investigate whether CCD8 synthesize CL-like compounds from other 9-cis-configured apocarotenoids to confirm their presence and synthesis in planta. We showed that CCD8 enzymes from different plants produce a hydroxylated carlactone (3-H-CL) from 9-cis-3-OH-β-apo-10’-carotenal in vitro. In addition, we detected 3-H-CL in Nicotiana benthamiana leaves transiently expressing the CL biosynthesis enzymes from rice and Arabidopsis. 3-H-CL is biologically active, as shown by Striga hermonthica seed germination assay and by its effect on the high-tillering phenotype of the rice d10 mutant. We also confirmed that 3-H-CL is a natural metabolite by detecting it in roots of the rice SL perception mutant d14. In a second project, we investigated the activity of three rice CCDs in vitro and showed that one of them (zaxinone synthase; ZAS) is an apocarotenoid cleavage enzyme with a clear preference for the substrate all-trans-3-OH-β-apo-10’-carotenal, as suggested by a kinetic study. ZAS produces two products, the C18 ketone zaxinone and an unstable C9 dialdehyde that could be identified by LC-MS after derivatization. Activity tests were performed with crude lysates of overexpressing Escherichia coli cells and with purified enzyme. We established that zaxinone is a natural metabolite present in planta. Investigations of a corresponding rice mutant (zas) and activity bioassays performed by our group demonstrate that zaxinone a novel signaling molecule required for normal rice growth and development.
    Citation
    Baz, L. (2018). Biosynthesis of Carotenoid-Derived Plant Signaling Molecules. KAUST Research Repository. https://doi.org/10.25781/KAUST-EJG96
    DOI
    10.25781/KAUST-EJG96
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-EJG96
    Scopus Count
    Collections
    Biological and Environmental Sciences and Engineering (BESE) Division; Bioscience Program; Dissertations

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