ORANGE Represses Chloroplast Biogenesis in Etiolated Arabidopsis Cotyledons via Interaction with TCP14

First author: Tianhu Sun; Affiliations: Nanjing University (南京大学): Nanjing, China

Corresponding author: Shan Lu

The conversion of etioplasts into chloroplasts in germinating cotyledons is a crucial transition for higher plants, enabling photoautotrophic  growth upon illumination. Tight coordination of chlorophyll biosynthesis and photosynthetic complex assembly is critical for this process. ORANGE (OR), a DnaJ-like zinc finger domain-containing protein, was reported to trigger the biogenesis of carotenoid-accumulating plastids by promoting carotenoid biosynthesis and sequestration. Both nuclear and plastidic localizations of OR have been observed. Here, we show that Arabidopsis thaliana OR (At-OR) physically interacts with the transcription factor TCP14 in the nucleus and represses its transactivation activity. Through this interaction, the nucleus-localized OR negatively regulates expression of EARLY LIGHT-INDUCIBLE PROTEINS (ELIPs), reduces chlorophyll biosynthesis and delays development of thylakoid membranes in the plastids of germinating cotyledons. Nuclear abundance of OR decreased upon illumination. Together with an accumulation of TCP14 in the nucleus, this derepresses chloroplast biogenesis during de-etiolation. TCP14 is epistatic to OR and expression ofELIPs is directly regulated by the binding of TCP14 to Up1 elements in the ELIP promoter regions. Our results demonstrate that the interaction between OR and TCP14 in the nucleus leads to repression of chloroplast biogenesis in etiolated seedlings and provide new insights into the regulation of early chloroplast development.

在发芽的子叶中，原生质体向叶绿体的转化使得植物能够在光照条件下光合自养生长，所以该过程对于植物来说是不可或缺的。叶绿素生物合成与光合复合物组装的紧密配合对于该过程至关重要。ORANGE是一个含有类DnaJ锌指蛋白结构域的蛋白，该蛋白能够通过促进类胡萝卜素的生物合成和隔离诱导积累类胡萝卜素质体的合成。ORANGE的核定位和质体定位已经明了。本文中，作者的研究显示拟南芥的ORANGE蛋白能够与转录因子TCP14在核中发生物理互作，并且抑制其反式激活活性。通过该互作，核定位的ORANGE负调控ELIP的表达，减少叶绿素生物合成，并且延缓萌芽子叶质体中的类囊体膜发育。光照能够降低核中ORANGE的含量。与核中TCP14的积累一起，在植物去黄化过程中解除对于叶绿素生物合成的抑制。TCP14对于ORANGE具有上位性，并且TCP14直接结合到ELIP启动子区域的Up1元件上调控ELIP的表达。本文的结果揭示了黄化苗中ORANGE与TCP14在核中的互作抑制了叶绿体的生物发生，为早期叶绿体发育的分子调控机制提供了新的视野。

通讯：卢山（https://life.nju.edu.cn/ls_14014/list.htm）

研究方向：1. 类胡萝卜素的代谢及其调控机制；2. 与质体发育相关的转录因子及其功能调控；3. 植物进化早期的类胡萝卜素代谢过程。

doi: https://doi.org/10.1105/tpc.18.00290

Journal: Plant Cell

First Published: October 11, 2019