Singh Prashant, Kaloudas Dimitrios, Raines Christine A
Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK.
J Exp Bot. 2008;59(14):3975-85. doi: 10.1093/jxb/ern236. Epub 2008 Oct 28.
The chloroplast protein CP12 has been shown to regulate the activity of two Calvin cycle enzymes, phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), by the reversible formation of a multiprotein complex. In Arabidopsis there are three CP12 genes, CP12-1, CP12-2, and CP12-3, and expression analysis suggested that the function of these proteins may not be restricted to the Calvin cycle. Reverse transcription-PCR analysis was used here to investigate further the expression patterns of the three CP12 Arabidopsis genes together with the genes encoding plastid GAPDH (GAPA-1 and GAPB), PRK (PRK), and plastid NAD-dependent GAPDH (GAPCp1 and GAPCp2) during development, in response to changes in light, temperature, and anaerobic conditions. Expression of the CP12-2 gene was similar to that of the Calvin cycle enzymes PRK and GAPDH. However, this was not the case for CP12-1 and -3 which were both expressed in roots. Analysis of transgenic Arabidopsis lines expressing CP12::GUS fusion constructs revealed that the CP12 genes display different spatiotemporal expression patterns. The CP12-1 gene was expressed in root tips whilst CP12-3::GUS expression was evident throughout the root tissue. The most unexpected finding was that all three CP12 genes were expressed in floral tissues; CP12-1 and CP12-2 expression was detected in the sepals and the style of the flower, while in contrast CP12-3::GUS expression was restricted to the stigma and anthers. Taken together, the data suggest that the redox-sensitive CP12 proteins may have a wider role in non-photosynthetic plastids, throughout the plant life cycle.
叶绿体蛋白CP12已被证明可通过多蛋白复合物的可逆形成来调节卡尔文循环中的两种酶——磷酸核酮糖激酶（PRK）和甘油醛-3-磷酸脱氢酶（GAPDH）的活性。拟南芥中有三个CP12基因，即CP12-1、CP12-2和CP12-3，表达分析表明这些蛋白的功能可能不限于卡尔文循环。本文采用逆转录PCR分析，进一步研究了拟南芥三个CP12基因以及编码质体GAPDH（GAPA-1和GAPB）、PRK（PRK）和质体NAD依赖型GAPDH（GAPCp1和GAPCp2）的基因在发育过程中、对光照、温度和厌氧条件变化的响应中的表达模式。CP12-2基因的表达与卡尔文循环酶PRK和GAPDH的表达相似。然而，CP12-1和-3并非如此，它们在根中均有表达。对表达CP12::GUS融合构建体的转基因拟南芥株系的分析表明，CP12基因呈现出不同的时空表达模式。CP12-1基因在根尖表达，而CP12-3::GUS在整个根组织中均有明显表达。最出乎意料的发现是，所有三个CP12基因在花组织中均有表达；在花的萼片和花柱中检测到CP12-1和CP12-2的表达，而相比之下，CP12-3::GUS的表达仅限于柱头和花药。综上所述，数据表明对氧化还原敏感的CP12蛋白可能在整个植物生命周期的非光合质体中发挥更广泛的作用。
