Lara María Valeria, Chuong Simon D X, Akhani Hossein, Andreo Carlos Santiago, Edwards Gerald E
Centro de Estudios Fotosintéticos y Bioquímicos, Facultad de Ciencias Bioquímicas y Farmacéuticas, Rosario 2000, Argentina.
Plant Physiol. 2006 Oct;142(2):673-84. doi: 10.1104/pp.106.085829. Epub 2006 Aug 18.
Spatial and temporal regulation of phosphoenolpyruvate carboxylase (PEPC) is critical to the function of C(4) photosynthesis. The photosynthetic isoform of PEPC in the cytosol of mesophyll cells in Kranz-type C(4) photosynthesis has distinctive kinetic and regulatory properties. Some species in the Chenopodiaceae family perform C(4) photosynthesis without Kranz anatomy by spatial separation of initial fixation of atmospheric CO(2) via PEPC from C(4) acid decarboxylation and CO(2) donation to Rubisco within individual chlorenchyma cells. We studied molecular and functional features of PEPC in two single-cell functioning C(4) species (Bienertia sinuspersici, Suaeda aralocaspica) as compared to Kranz type (Haloxylon persicum, Salsola richteri, Suaeda eltonica) and C(3) (Suaeda linifolia) chenopods. It was found that PEPC from both types of C(4) chenopods displays higher specific activity than that of the C(3) species and shows kinetic and regulatory characteristics similar to those of C(4) species in other families in that they are subject to light/dark regulation by phosphorylation and display differential malate sensitivity. Also, the deduced amino acid sequence from leaf cDNA indicates that the single-cell functioning C(4) species possesses a Kranz-type C(4) isoform with a Ser in the amino terminal. A phylogeny of PEPC shows that isoforms in the two single-cell functioning C(4) species are in a clade with the C(3) and Kranz C(4) Suaeda spp. with high sequence homology. Overall, this study indicates that B. sinuspersici and S. aralocaspica have a C(4)-type PEPC similar to that in Kranz C(4) plants, which likely is required for effective function of C(4) photosynthesis.
磷酸烯醇式丙酮酸羧化酶（PEPC）的时空调节对于C4光合作用的功能至关重要。在花环型C4光合作用中，叶肉细胞胞质溶胶中的光合型PEPC具有独特的动力学和调节特性。藜科的一些物种通过在单个叶肉细胞内将大气CO2经PEPC的初始固定与C4酸脱羧以及向Rubisco的CO2供体进行空间分离，从而在没有花环结构的情况下进行C4光合作用。我们研究了两种单细胞功能C4物种（海滨盐角草、阿拉善碱蓬）中PEPC的分子和功能特征，并与花环型（梭梭、里海猪毛菜、埃尔顿碱蓬）和C3（亚麻叶碱蓬）藜科植物进行了比较。结果发现，两种C4藜科植物的PEPC比C3物种具有更高的比活性，并且在动力学和调节特性上与其他科的C4物种相似，即它们受磷酸化的光/暗调节并表现出不同的苹果酸敏感性。此外，从叶片cDNA推导的氨基酸序列表明，单细胞功能C4物种拥有一种在氨基末端带有丝氨酸的花环型C4同工型。PEPC的系统发育表明，两种单细胞功能C4物种中的同工型与C3和花环型C4碱蓬属植物处于一个进化枝中，具有高度的序列同源性。总体而言，这项研究表明海滨盐角草和阿拉善碱蓬具有与花环型C4植物相似的C4型PEPC，这可能是C4光合作用有效发挥功能所必需的。
