Waters Mark T, Moylan Elizabeth C, Langdale Jane A
Department of Plant Sciences, University of Oxford, South Parks Rd, Oxford OX1 3RB, UK.
Plant J. 2008 Nov;56(3):432-44. doi: 10.1111/j.1365-313X.2008.03616.x. Epub 2008 Aug 4.
In a number of land plants, Golden2-like (GLK) genes encode a pair of partially redundant nuclear transcription factors that are required for the expression of nuclear photosynthetic genes and for chloroplast development. As chloroplast biogenesis depends on close co-operation between the nuclear and plastid compartments, GLK gene function must be dependent on tight intracellular control. However, the extent to which GLK-mediated chloroplast development depends on intercellular communication is not known. Here we used sector analysis to show that GLK proteins operate cell-autonomously in leaf mesophyll cells. To establish whether GLK proteins are able to influence adjacent cell layers, we used tissue-specific promoters to restrict GLK gene expression to the epidermis and to the phloem. GLK genes driven by the Arabidopsis epidermal FIDDLEHEAD (FDH) and MERISTEM LAYER1 (AtML1) promoters failed to rescue the pale-green Atglk1 Atglk2 mutant phenotype, confirming the suggestion that GLK proteins can only influence chloroplast development intracellularly. An exception to this rule was seen in lines in which GLK genes were expressed in the phloem. However, we believe that the partial complementation of the mutant phenotype that was observed resulted from phloem unloading, as opposed to inherent properties of GLK proteins. We conclude that GLK proteins act in a cell-autonomous manner to coordinate and maintain the photosynthetic apparatus within individual cells. Significantly, this suggests that GLK proteins provide a means to fine-tune photosynthesis according to the differential requirements of cells within the leaf.
在许多陆地植物中，类Golden2（GLK）基因编码一对部分冗余的核转录因子，这些因子是核光合基因表达和叶绿体发育所必需的。由于叶绿体生物发生依赖于细胞核和质体区室之间的紧密协作，GLK基因的功能必然依赖于严格的细胞内调控。然而，GLK介导的叶绿体发育在多大程度上依赖于细胞间通讯尚不清楚。在这里，我们使用扇形分析表明GLK蛋白在叶肉细胞中自主发挥作用。为了确定GLK蛋白是否能够影响相邻细胞层，我们使用组织特异性启动子将GLK基因的表达限制在表皮和韧皮部。由拟南芥表皮FIDDLEHEAD（FDH）和分生组织层1（AtML1）启动子驱动的GLK基因未能挽救浅绿色的Atglk1 Atglk2突变体表型，证实了GLK蛋白只能在细胞内影响叶绿体发育的观点。在韧皮部表达GLK基因的株系中发现了一个例外情况。然而，我们认为观察到的突变体表型的部分互补是由于韧皮部卸载，而不是GLK蛋白的固有特性。我们得出结论，GLK蛋白以细胞自主的方式发挥作用，以协调和维持单个细胞内的光合装置。重要的是，这表明GLK蛋白提供了一种根据叶片内细胞的不同需求来微调光合作用的手段。
