Engelmann Sascha, Zogel Corinna, Koczor Maria, Schlue Ute, Streubel Monika, Westhoff Peter
Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität, Universitätsstr, 1, 40225 Düsseldorf, Germany.
BMC Plant Biol. 2008 Jan 21;8:4. doi: 10.1186/1471-2229-8-4.
The key enzymes of photosynthetic carbon assimilation in C4 plants have evolved independently several times from C3 isoforms that were present in the C3 ancestral species. The C4 isoform of phosphoenolpyruvate carboxylase (PEPC), the primary CO2-fixing enzyme of the C4 cycle, is specifically expressed at high levels in mesophyll cells of the leaves of C4 species. We are interested in understanding the molecular changes that are responsible for the evolution of this C4-characteristic PEPC expression pattern, and we are using the genus Flaveria (Asteraceae) as a model system. It is known that cis-regulatory sequences for mesophyll-specific expression of the ppcA1 gene of F. trinervia (C4) are located within a distal promoter region (DR).
In this study we focus on the proximal region (PR) of the ppcA1 promoter of F. trinervia and present an analysis of its function in establishing a C4-specific expression pattern. We demonstrate that the PR harbours cis-regulatory determinants which account for high levels of PEPC expression in the leaf. Our results further suggest that an intron in the 5' untranslated leader region of the PR is not essential for the control of ppcA1 gene expression.
The allocation of cis-regulatory elements for enhanced expression levels to the proximal region of the ppcA1 promoter provides further insight into the regulation of PEPC expression in C4 leaves.
C4植物中光合碳同化的关键酶已从C3祖先物种中存在的C3同工型独立进化了数次。磷酸烯醇式丙酮酸羧化酶（PEPC）的C4同工型是C4循环的主要CO2固定酶，在C4物种叶片的叶肉细胞中特异性高表达。我们有兴趣了解导致这种C4特征性PEPC表达模式进化的分子变化，并且我们正在使用黄顶菊属（菊科）作为模型系统。已知三脉叶黄顶菊（C4）的ppcA1基因叶肉特异性表达的顺式调控序列位于远端启动子区域（DR）内。
在本研究中，我们聚焦于三脉叶黄顶菊ppcA1启动子的近端区域（PR），并对其在建立C4特异性表达模式中的功能进行分析。我们证明PR包含顺式调控决定因素，这些因素导致叶片中PEPC的高水平表达。我们的结果进一步表明，PR的5'非翻译前导区域中的一个内含子对于ppcA1基因表达的控制不是必需的。
将用于增强表达水平的顺式调控元件定位到ppcA1启动子的近端区域，为深入了解C4叶片中PEPC表达的调控提供了进一步的线索。
