Rao Srinath K, Magnin Noël C, Reiskind Julia B, Bowes George
Department of Botany, 220 Bartram Hall, P.O. Box 118526, University of Florida, Gainesville, FL 32611-8526, USA.
Plant Physiol. 2002 Oct;130(2):876-86. doi: 10.1104/pp.008045.
The submersed monocot Hydrilla verticillata (L.f.) Royle is a facultative C(4) plant. It typically exhibits C(3) photosynthetic characteristics, but exposure to low [CO(2)] induces a C(4) system in which the C(4) and Calvin cycles co-exist in the same cell and the initial fixation in the light is catalyzed by phosphoenolpyruvate carboxylase (PEPC). Three full-length cDNAs encoding PEPC were isolated from H. verticillata, two from leaves and one from root. The sequences were 95% to 99% identical and shared a 75% to 85% similarity with other plant PEPCs. Transcript studies revealed that one isoform, Hvpepc4, was exclusively expressed in leaves during C(4) induction. This and enzyme kinetic data were consistent with it being the C(4) photosynthesis isoform. However, the C(4) signature serine of terrestrial plant C(4) isoforms was absent in this and the other H. verticillata sequences. Instead, alanine, typical of C(3) sequences, was present. Western analyses of C(3) and C(4) leaf extracts after anion-exchange chromatography showed similar dominant PEPC-specific bands at 110 kD. In phylogenetic analyses, the sequences grouped with C(3), non-graminaceous C(4), and Crassulacean acid metabolism PEPCs but not with the graminaceous C(4), and formed a clade with a gymnosperm, which is consistent with H. verticillata PEPC predating that of other C(4) angiosperms.
沉水单子叶植物黑藻（Hydrilla verticillata (L.f.) Royle）是兼性C4植物。它通常表现出C3光合作用特征，但暴露于低[CO2]环境会诱导形成一种C4系统，其中C4和卡尔文循环在同一细胞中共存，且光下的初始固定由磷酸烯醇式丙酮酸羧化酶（PEPC）催化。从黑藻中分离出了三个编码PEPC的全长cDNA，两个来自叶片，一个来自根部。这些序列的相似度为95%至99%，与其他植物的PEPC有75%至85%的相似性。转录研究表明，一种同工型Hvpepc4在C4诱导过程中仅在叶片中表达。这一点和酶动力学数据都表明它是C4光合作用同工型。然而，该序列以及其他黑藻序列中不存在陆生植物C4同工型特有的丝氨酸残基。相反，存在C3序列典型的丙氨酸残基。对C3和C4叶片提取物进行阴离子交换色谱分析后的Western分析显示，在110 kD处有相似的主要PEPC特异性条带。在系统发育分析中，这些序列与C3、非禾本科C4和景天酸代谢PEPC归为一类，但不与禾本科C4归为一类，并且与一种裸子植物形成一个分支，这与黑藻的PEPC早于其他C4被子植物的PEPC一致。
