title: Functional modeling identifies paralogous solanesyl-diphosphate synthases that assemble the side chain of plastoquinone-9 in plastids.
abstract: It is a little known fact that plastoquinone-9, a vital redox cofactor of photosynthesis, doubles as a precursor for the biosynthesis of a vitamin E analog called plastochromanol-8, the physiological significance of which has remained elusive. Gene network reconstruction, GFP fusion experiments, and targeted metabolite profiling of insertion mutants indicated that Arabidopsis possesses two paralogous solanesyl-diphosphate synthases, AtSPS1 (At1g78510) and AtSPS2 (At1g17050), that assemble the side chain of plastoquinone-9 in plastids. Similar paralogous pairs were detected throughout terrestrial plant lineages but were not distinguished in the literature and genomic databases from mitochondrial homologs involved in the biosynthesis of ubiquinone. The leaves of the atsps2 knock-out were devoid of plastochromanol-8 and displayed severe losses of both non-photoactive and photoactive plastoquinone-9, resulting in near complete photoinhibition at high light intensity. Such a photoinhibition was paralleled by significant damage to photosystem II but not to photosystem I. In contrast, in the atsps1 knock-out, a small loss of plastoquinone-9, restricted to the non-photoactive pool, was sufficient to eliminate half of the plastochromanol-8 content of the leaves. Taken together, these results demonstrate that plastochromanol-8 originates from a subfraction of the non-photoactive pool of plastoquinone-9. In contrast to other plastochromanol-8 biosynthetic mutants, neither the single atsps knock-outs nor the atsps1 atsps2 double knock-out displayed any defects in tocopherols accumulation or germination.
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Anna
authors.initials: A
authors.lastname: Block
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095.
authors.forename: Rikard
authors.initials: R
authors.lastname: Fristedt
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Sara
authors.initials: S
authors.lastname: Rogers
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Jyothi
authors.initials: J
authors.lastname: Kumar
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Brian
authors.initials: B
authors.lastname: Barnes
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Joshua
authors.initials: J
authors.lastname: Barnes
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Elowsky
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Yashitola
authors.initials: Y
authors.lastname: Wamboldt
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588.
authors.forename: Sally A
authors.initials: SA
authors.lastname: Mackenzie
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287.
authors.forename: Kevin
authors.initials: K
authors.lastname: Redding
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095.
authors.forename: Sabeeha S
authors.initials: SS
authors.lastname: Merchant
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, Nebraska 68588. Electronic address: gbasset2@unl.edu.
authors.forename: Gilles J
authors.initials: GJ
authors.lastname: Basset
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D002839:Chromans / Q000378:metabolism; D055785:Gene Knockdown Techniques; D018525:Germination / Q000502:physiology; D008954:Models, Biological; D045331:Photosystem I Protein Complex / Q000096:biosynthesis / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000096:biosynthesis / Q000235:genetics; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism*; D024505:Tocopherols / Q000378:metabolism; D014810:Vitamin E / Q000031:analogs & derivatives / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D002839:Chromans; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014810:Vitamin E; C013649:plastochromanol 8; D019883:Alkyl and Aryl Transferases; C500830:SPS1 protein, Arabidopsis; C500831:SPS2 protein, Arabidopsis; D010971:Plastoquinone; D024505:Tocopherols
keywords: Arabidopsis; Photosystem II; Quinones; Terpenoids; Vitamin E
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