Romer, Jill: The role of the salvage pathway of phytol, geranylgeraniol, and farnesol phosphorylation in Arabidopsis thaliana. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-61530
@phdthesis{handle:20.500.11811/8962,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-61530,
author = {{Jill Romer}},
title = {The role of the salvage pathway of phytol, geranylgeraniol, and farnesol phosphorylation in Arabidopsis thaliana},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = mar,

note = {The isoprenoid alcohol phytol can be phosphorylated in Arabidopsis to phytyl-phosphate (phytyl-P) by the phytol kinase (VTE5) and further to phytyl-diphosphate (phytyl-PP) by the phytyl phosphate kinase (VTE6). Phytyl-PP derived from phytol phosphorylation enters the biosynthesis of tocopherol and phylloquinone. Arabidopsis phytol kinase mutant plants (vte5) still contain reduced levels of tocopherol, while phytyl phosphate kinase mutant plants (vte6) are tocopherol deficient. One homolog of VTE5 in Arabidopsis was identified and later designated FOLK for farnesol kinase. FOLK is able to phosphorylate farnesol, geraniol, and geranylgeraniol. In this work, the role of phytol, geranylgeraniol, and farnesol phosphorylation, for the biosynthesis of different metabolites including tocopherol (vitamin E) and phylloquinone (vitamin K1), was investigated in Arabidopsis vte5-2, folk-2, and vte5-2 folk-2 mutant plants.
Phytyl-P and geranylgeranyl-P levels are reduced, while phytol accumulates in vte5-2 and vte5-2 folk-2. Geranylgeraniol accumulates in folk-2 and vte5-2 folk-2. The vte5-2 single mutant shows reduced tocopherol levels, while the folk-2 single mutant plants have similar tocopherol levels as the WT. The phylloquinone levels are similar to the WT in vte5-2 and in folk-2. The vte5-2 folk-2 double mutant plants are tocopherol deficient and have a reduced content of phylloquinone in comparison to the WT. Therefore, the farnesol kinase (FOLK) and the phytol kinase (VTE5) are involved in tocopherol and phylloquinone biosynthesis. Enzyme assays with recombinant proteins expressed in E. coli revealed that VTE5 is able to phosphorylate phytol, geranylgeraniol, and farnesol, while FOLK only phosphorylated geranylgeraniol and farnesol but not phytol. Geranylgeranyl-PP is the precursor for the biosynthesis of chlorophyll and carotenoids. The contents of chlorophyll and carotenoids were not altered in the mutants indicating that VTE5 and FOLK are not required for the biosynthesis of these compounds. The sterol content was slightly reduced in the vte5-2 folk-2 double mutant suggesting that farnesol phosphorylation by VTE5 and FOLK contributes to sterol synthesis.
Arabidopsis mutant plants lacking phytyl phosphate kinase (VTE6) activity show a strong growth retardation. The decreased growth of vte6-1 could not be rescued by supplementation with gibberellic acid. Arabidopsis vte6 mutants were described to accumulate phytyl-P and phytol derived from chlorophyll degradation. Accumulation of phytyl-P might be detrimental for plant growth and therefore cause the severe growth phenotype. The introduction of the pao1 mutation, affected in chlorophyll degradation, into the vte6-1 background did not rescue the retarded growth of vte6-1. The vte6-1 pao1 plants were still only viable on synthetic medium supplemented with sucrose. Nevertheless, some plants grew slightly better and developed shoots but no siliques nor seeds.
In conclusion, Arabidopsis farnesol kinase FOLK and the phytol kinase VTE5 are involved in the biosynthesis of tocopherol and phylloquinone. Tocopherol and phylloquinone synthesis depends on the availability of phytyl-PP. However, the recombinant FOLK protein does not show in vitro phytol kinase activity. Presumably, the geranylgeraniol kinase activity of FOLK contributes to tocopherol and phylloquinone biosynthesis. This shows the important role of geranylgeraniol phosphorylation next to phytol phosphorylation for tocopherol and phylloquinone biosynthesis in Arabidopsis.},

url = {https://hdl.handle.net/20.500.11811/8962}
}

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