Chlorophyll Degradation: The Tocopherol Biosynthesis-Related Phytol Hydrolase in Arabidopsis Seeds Is Still Missing
Chlorophyll Degradation: The Tocopherol Biosynthesis-Related Phytol Hydrolase in Arabidopsis Seeds Is Still Missing
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叶绿素降解：拟南芥种子中与生育酚生物合成相关的植醇水解酶仍然缺失
DOI：
10.1104/pp.114.243709
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发表时间：
2014
期刊：
影响因子：
7.4
通讯作者：
Zhang Chunyu
中科院分区：
文献类型：
--
作者：
Zhang Wei;Liu Tianqi;Ren Guodong;Hoertensteiner Stefan;Zhou Yongming;Cahoon Edgar B.;Zhang Chunyu
植基二磷酸（PDP）是生育酚生物合成的异戊二烯基前体。基于最近的遗传证据，PDP主要通过叶绿素降解和顺序的植醇磷酸化提供给生育酚生物合成途径。已知拟南芥（Arabidopsis thaliana）的三种酶能够在体外从叶绿素去除叶绿醇链：叶绿素酶1（CLH 1）、CLH 2和脱镁叶绿素脱镁叶绿酸水解酶（PPH），其特异性地水解脱镁叶绿素。虽然PPH，而不是叶绿素酶，是必需的在体内叶绿素分解过程中拟南芥叶片衰老，很少有人知道这些植物醇释放酶参与生育酚的生物合成。为了探索PDP的生育酚合成的起源，种子生育酚的浓度进行了测定，在拟南芥种子特异性过表达的PPH和在单一和多个突变体中的三个基因编码已知的脱植酸酶的工程线。除了在PPH过表达中观察到生育酚含量适度增加外，其余品系均未表现出生育酚浓度显着降低，这表明已知的叶绿素衍生的植醇释放酶在生育酚生物合成中不发挥主要作用。生育酚含量的种子从双突变体NONYELLOWING1（NYE1）和NYE2，叶绿素降解的调节剂，有适度的减少与野生型种子相比，虽然成熟的种子的双突变体保留显着较高的叶绿素水平。这些研究结果表明，NYE可能发挥有限的作用，在调节未知的生育酚生物合成相关的植醇水解酶。同时，野生型过表达NYE 1的种子生育酚水平较低，表明NYE 1依赖的叶绿素降解产生的植醇可能没有进入生育酚的生物合成。叶绿素降解的潜在途径进行了讨论生育酚的生物合成。
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.