C4 photosynthesis has evolved independently in over sixty lineages and in so doing repurposed existing enzymes to drive a carbon pump that limits the RuBisCO oxygenation reaction. In all cases, gene expression is modified such that C4 proteins accumulate to levels matching those of the photosynthetic apparatus. To better understand this rewiring of gene expression we undertook RNA- and DNaseI-SEQ on de-etiolating seedlings of C4 Gynandropsis gynandra, which is sister to C3 Arabidopsis. Changes in chloroplast ultrastructure and C4 gene expression were coordinated and rapid. C3 photosynthesis and C4 genes showed similar induction patterns, but C4 genes from G. gynandra were more strongly induced than orthologs from Arabidopsis. A gene regulatory network predicted transcription factors operating at the top of the de-etiolation network, including those responding to light, act upstream of C4 genes. Light responsive elements, especially G-, E- and GT-boxes were over-represented in accessible chromatin around C4 genes. Moreover, in vivo binding of many G-, E- and GT-boxes was detected. Overall, the data support a model in which rapid and robust C4 gene expression following light exposure is generated through modifications in cis to allow integration into high-level transcriptional networks including those underpinned by conserved light responsive elements.

中文翻译：

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C4基因的诱导通过顺式改变而进化，从而可以整合到祖先的C3基因调控网络中

C4的光合作用已经在60多个世系中独立发展，因此重新利用了现有的酶来驱动碳泵，从而限制了RuBisCO的氧化反应。在所有情况下，基因表达都经过修饰，以使C4蛋白积累到与光合作用设备相匹配的水平。为了更好地理解基因表达的这种重新结合，我们对C3拟南芥的姊妹C4绞股蓝（Gynandropsis gynandra）幼苗进行了去雄化处理，对其进行了RNA-和DNaseI-SEQ测序。叶绿体超微结构和C4基因表达的变化是协调和迅速的。C3光合作用和C4基因显示相似的诱导模式，但是来自G. gynandra的C4基因比拟南芥的直向同源物诱导更强烈。一个基因调控网络预测转录因子在去异黄酮化网络的顶部运行，包括那些对光有反应的生物，在C4基因的上游起作用。光响应元件，尤其是G-，E-和GT-boxs在C4基因周围的易染色质中过分代表。而且，检测到许多G-，E-和GT-box的体内结合。总体而言，数据支持一个模型，其中通过顺式修饰可产生曝光后快速且稳定的C4基因表达，以允许整合到高级转录网络中，包括那些由保守的光响应元件支持的转录网络。