Phytyl-diphosphate, which provides phytyl moieties as a common substrate in both tocopherol and phyllo- quinone biosynthesis, derives from de novo isoprenoid biosynthesis or a salvage pathway via phytol phos- phorylat...Phytyl-diphosphate, which provides phytyl moieties as a common substrate in both tocopherol and phyllo- quinone biosynthesis, derives from de novo isoprenoid biosynthesis or a salvage pathway via phytol phos- phorylation. However, very little is known about the role and origin of the phytyl moiety for phylloquinone biosynthesis. Since VTE6, a phytyl-phosphate kinase, is a key enzyme for phytol phosphorylation, we char- acterized Arabidopsis vte6 mutants to gain insight into the roles of phytyl moieties in phylloquinone biosyn- thesis and of phylloquinone in photosystem I （PSI） biogenesis. The VTE6 knockout mutants vte6-1 and vte6-2 lacked detectable phylloquinone, whereas the phylloquinone content in the VTE6 knockdown mutant vte6-3 was 90% lower than that in wild-type. In vte6 mutants, PSI function was impaired and accu- mulation of the PSI complex was defective. The PSI core subunits PsaA/B were efficiently synthesized and assembled into the PSI complex in vte6-3. However, the degradation rate of PSI subunits in the assembled PSI complex was more rapid in vte6-3 than in wild-type. In vte6-3, PSI was more susceptible to high-light damage than in wild-type. Our results provide the first genetic evidence that the phytol phosphorylation pathway is essential for phylloquinone biosynthesis, and that phylloquinone is required for PSI complex stability.展开更多
文摘Phytyl-diphosphate, which provides phytyl moieties as a common substrate in both tocopherol and phyllo- quinone biosynthesis, derives from de novo isoprenoid biosynthesis or a salvage pathway via phytol phos- phorylation. However, very little is known about the role and origin of the phytyl moiety for phylloquinone biosynthesis. Since VTE6, a phytyl-phosphate kinase, is a key enzyme for phytol phosphorylation, we char- acterized Arabidopsis vte6 mutants to gain insight into the roles of phytyl moieties in phylloquinone biosyn- thesis and of phylloquinone in photosystem I （PSI） biogenesis. The VTE6 knockout mutants vte6-1 and vte6-2 lacked detectable phylloquinone, whereas the phylloquinone content in the VTE6 knockdown mutant vte6-3 was 90% lower than that in wild-type. In vte6 mutants, PSI function was impaired and accu- mulation of the PSI complex was defective. The PSI core subunits PsaA/B were efficiently synthesized and assembled into the PSI complex in vte6-3. However, the degradation rate of PSI subunits in the assembled PSI complex was more rapid in vte6-3 than in wild-type. In vte6-3, PSI was more susceptible to high-light damage than in wild-type. Our results provide the first genetic evidence that the phytol phosphorylation pathway is essential for phylloquinone biosynthesis, and that phylloquinone is required for PSI complex stability.
