Department of Botany and Plant Sciences, Institute for Integrative Genome Biology, University of California, Riverside, CA, 92521, USA.
Department of Biology, Duke University, Durham, NC, 27708, USA.
Nat Commun. 2019 Jun 14;10(1):2630. doi: 10.1038/s41467-019-10517-1.
Phytochromes initiate chloroplast biogenesis by activating genes encoding the photosynthetic apparatus, including photosynthesis-associated plastid-encoded genes (PhAPGs). PhAPGs are transcribed by a bacterial-type RNA polymerase (PEP), but how phytochromes in the nucleus activate chloroplast gene expression remains enigmatic. We report here a forward genetic screen in Arabidopsis that identified NUCLEAR CONTROL OF PEP ACTIVITY (NCP) as a necessary component of phytochrome signaling for PhAPG activation. NCP is dual-targeted to plastids and the nucleus. While nuclear NCP mediates the degradation of two repressors of chloroplast biogenesis, PIF1 and PIF3, NCP in plastids promotes the assembly of the PEP complex for PhAPG transcription. NCP and its paralog RCB are non-catalytic thioredoxin-like proteins that diverged in seed plants to adopt nonredundant functions in phytochrome signaling. These results support a model in which phytochromes control PhAPG expression through light-dependent double nuclear and plastidial switches that are linked by evolutionarily conserved and dual-localized regulatory proteins.
光敏色素通过激活编码光合作用装置的基因（包括与光合作用相关的质体编码基因[PhAPGs]）来启动叶绿体生物发生。PhAPGs 由细菌型 RNA 聚合酶（PEP）转录，但核中的光敏色素如何激活叶绿体基因表达仍然是个谜。我们在这里报告了一个在拟南芥中的正向遗传学筛选，该筛选确定了核控制 PEP 活性（NCP）作为光敏色素信号转导激活 PhAPG 的必需组成部分。NCP 被双重靶向到质体和细胞核。虽然核 NCP 介导了两个叶绿体生物发生抑制剂 PIF1 和 PIF3 的降解，但质体中的 NCP 促进了 PEP 复合物的组装，以进行 PhAPG 转录。NCP 和其同源物 RCB 是非催化型的硫氧还蛋白样蛋白，在种子植物中分化，以在光敏色素信号转导中采用非冗余的功能。这些结果支持了一个模型，即光敏色素通过光依赖性的双重核和质体开关来控制 PhAPG 的表达，这些开关通过进化保守且双重定位的调节蛋白连接。
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