title: Chlorophyll degradation: the tocopherol biosynthesis-related phytol hydrolase in Arabidopsis seeds is still missing.
abstract: Phytyl diphosphate (PDP) is the prenyl precursor for tocopherol biosynthesis. Based on recent genetic evidence, PDP is supplied to the tocopherol biosynthetic pathway primarily by chlorophyll degradation and sequential phytol phosphorylation. Three enzymes of Arabidopsis (Arabidopsis thaliana) are known to be capable of removing the phytol chain from chlorophyll in vitro: chlorophyllase1 (CLH1), CLH2, and pheophytin pheophorbide hydrolase (PPH), which specifically hydrolyzes pheophytin. While PPH, but not chlorophyllases, is required for in vivo chlorophyll breakdown during Arabidopsis leaf senescence, little is known about the involvement of these phytol-releasing enzymes in tocopherol biosynthesis. To explore the origin of PDP for tocopherol synthesis, seed tocopherol concentrations were determined in Arabidopsis lines engineered for seed-specific overexpression of PPH and in single and multiple mutants in the three genes encoding known dephytylating enzymes. Except for modestly increasing tocopherol content observed in the PPH overexpressor, none of the remaining lines exhibited significantly reduced tocopherol concentrations, suggesting that the known chlorophyll-derived phytol-releasing enzymes do not play major roles in tocopherol biosynthesis. Tocopherol content of seeds from double mutants in NONYELLOWING1 (NYE1) and NYE2, regulators of chlorophyll degradation, had modest reduction compared with wild-type seeds, although mature seeds of the double mutant retained significantly higher chlorophyll levels. These findings suggest that NYEs may play limited roles in regulating an unknown tocopherol biosynthesis-related phytol hydrolase. Meanwhile, seeds of wild-type over-expressing NYE1 had lower tocopherol levels, suggesting that phytol derived from NYE1-dependent chlorophyll degradation probably doesn't enter tocopherol biosynthesis. Potential routes of chlorophyll degradation are discussed in relation to tocopherol biosynthesis.
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Wei
authors: W
authors: Zhang
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Tianqi
authors: T
authors: Liu
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Guodong
authors: G
authors: Ren
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Stefan
authors: S
authors: Hörtensteiner
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Yongming
authors: Y
authors: Zhou
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.).
authors: Edgar B
authors: EB
authors: Cahoon
authors: National Key Laboratory of Crop Genetic Improvement and College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China (W.Z., T.L., Y.Z., C.Z.);State Key Laboratory of Genetic Engineering and Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai 200433, China (G.R.);Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (S.H.); andCenter for Plant Science Innovation and Department of Biochemistry, University of Nebraska, Lincoln, Nebraska 68588 (E.B.C.) zhchy@mail.hzau.edu.cn.
authors: Chunyu
authors: C
authors: Zhang
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D006867:Hydrolases / Q000378:metabolism; D016254:Mutagenesis, Insertional; D010836:Phytol / Q000378:metabolism; D012639:Seeds / Q000378:metabolism*; D024505:Tocopherols / Q000378:metabolism*
chemical_list: D002734:Chlorophyll; D010836:Phytol; D006867:Hydrolases; D002265:Carboxylic Ester Hydrolases; C019875:chlorophyllase; D024505:Tocopherols