Pogson B, McDonald K A, Truong M, Britton G, DellaPenna D
Department of Plant Sciences, University of Arizona, Tucson 85721, USA.
Plant Cell. 1996 Sep;8(9):1627-39. doi: 10.1105/tpc.8.9.1627.
Lutein, a dihydroxy beta, epsilon-carotenoid, is the predominant carotenoid in photosynthetic plant tissue and plays a critical role in light-harvesting complex assembly and function. To further understand lutein synthesis and function, we isolated four lutein-deficient mutants of Arabidopsis that define two loci, lut1 and lut2 (for lutein deficient). These loci are required for lutein biosynthesis but not for the biosynthesis of beta, beta-carotenoids. The lut1 mutations are recessive, accumulate high levels of zeinoxanthin, which is the immediate precursor of lutein, and define lut1 as a disruption in epsilon ring hydroxylation. The lut2 mutations are semidominant, and their biochemical phenotype is consistent with a disruption of epsilon ring cyclization. The lut2 locus cosegregates with the recently isolated epsilon cyclase gene, thus, providing additional evidence that the lut2 alleles are mutations in the epsilon cyclase gene. It appears likely that the epsilon cyclase is a key step in regulating lutein levels and the ratio of lutein to beta,beta-carotenoids. Surprisingly, despite the absence of lutein, neither the lut1 nor lut2 mutation causes a visible deleterious phenotype or altered chlorophyll content, but both mutants have significantly higher levels of beta, beta-carotenoids. In particular, there is a stable increase in the xanthophyll cycle pigments (violaxanthin, antheraxanthin, and zeaxanthin) in both lut1 and lut2 mutants as well as an increase in zeinoxanthin in lut1 and beta-carotene in lut2. The accumulation of specific carotenoids is discussed as it pertains to the regulation of carotenoid biosynthesis and incorporation into the photosynthetic apparatus. Presumably, particular beta, beta-carotenoids are able to compensate functionally and structurally for lutein in the photosystems of Arabidopsis.
叶黄素是一种二羟基β,ε-类胡萝卜素，是光合植物组织中的主要类胡萝卜素，在捕光复合体的组装和功能中起关键作用。为了进一步了解叶黄素的合成和功能，我们分离出了拟南芥的四个叶黄素缺陷型突变体，它们定义了两个位点，lut1和lut2（代表叶黄素缺陷）。这些位点是叶黄素生物合成所必需的，但不是β,β-类胡萝卜素生物合成所必需的。lut1突变是隐性的，积累高水平的玉米黄质，玉米黄质是叶黄素的直接前体，这表明lut1是ε环羟基化过程中的一个破坏。lut2突变是半显性的，其生化表型与ε环环化的破坏一致。lut2位点与最近分离出的ε环化酶基因共分离，因此，这进一步证明lut2等位基因是ε环化酶基因中的突变。ε环化酶似乎是调节叶黄素水平以及叶黄素与β,β-类胡萝卜素比例的关键步骤。令人惊讶的是，尽管缺乏叶黄素，但lut1和lut2突变都不会导致明显的有害表型或叶绿素含量改变，但两个突变体的β,β-类胡萝卜素水平都显著更高。特别是，lut1和lut2突变体中叶黄素循环色素（紫黄质、环氧玉米黄质和玉米黄质）都有稳定增加，lut1中玉米黄质增加，lut2中β-胡萝卜素增加。文中讨论了特定类胡萝卜素的积累与类胡萝卜素生物合成调控以及并入光合机构的关系。据推测，特定的β,β-类胡萝卜素能够在功能和结构上补偿拟南芥光系统中的叶黄素。
