Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden.
Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
Physiol Plant. 2021 Mar;171(3):435-446. doi: 10.1111/ppl.13256. Epub 2020 Nov 20.
The plastid-encoded genes of higher plants are transcribed by at least two types of RNA polymerases, the nuclear-encoded RNA polymerase (NEP) and the plastid-encoded RNA polymerase (PEP). In mature photosynthesizing leaves, the vast majority of the genes are transcribed by PEP. However, the regulatory mechanisms controlling plastid transcription during early light response is unclear. Chloroplast development is suggested to be associated with a shift in the usage of the primary RNA polymerase from NEP to PEP as the expression of the plastid-encoded photosynthesis genes is induced upon light exposure. Assembly of the PEP complex has been suggested as a rate-limiting step for full activation of plastid-encoded photosynthesis gene expression. However, two sigma factor mutants, sig2 and sig6, with reduced PEP activity, showed significantly lower expression of the plastid-encoded photosynthesis genes already in the dark and during the first hours of light exposure indicating that PEP activity is required for basal expression of plastid-encoded photosynthesis genes in the dark and during early light response. Furthermore, in etioplasts and proplastids a fully assembled PEP complex was revealed on Blue Native PAGE. Our results indicate that a full assembly of the PEP complex is possible in the dark and that PEP drives basal transcriptional activity of plastid-encoded photosynthesis genes in the dark. Assembly of the complex is most likely not a rate-limiting step for full activation of plastid-encoded photosynthesis gene expression which is rather achieved either by the abundance of the PEP complex or by some posttranslational regulation of the individual PEP components.
高等植物的质体编码基因由至少两种 RNA 聚合酶转录，即核编码 RNA 聚合酶（NEP）和质体编码 RNA 聚合酶（PEP）。在成熟的光合作用叶片中，绝大多数基因由 PEP 转录。然而，在早期光反应中控制质体转录的调控机制尚不清楚。叶绿体发育与主要 RNA 聚合酶从 NEP 向 PEP 的使用转变有关，因为在光暴露下，质体编码的光合作用基因的表达被诱导。PEP 复合物的组装被认为是完全激活质体编码的光合作用基因表达的限速步骤。然而，两个 sigma 因子突变体 sig2 和 sig6，其 PEP 活性降低，在黑暗中和光暴露的头几个小时中，质体编码的光合作用基因的表达明显降低，表明 PEP 活性是黑暗中质体编码的光合作用基因基础表达和早期光反应所必需的。此外，在黄化质体和原质体中，在 Blue Native PAGE 上揭示了完全组装的 PEP 复合物。我们的结果表明，在黑暗中可以进行 PEP 复合物的完全组装，并且 PEP 驱动黑暗中质体编码的光合作用基因的基础转录活性。复合物的组装不太可能是完全激活质体编码的光合作用基因表达的限速步骤，这更可能是通过 PEP 复合物的丰度或单个 PEP 成分的某些翻译后调节来实现的。
