Kreiss Melanie, Haas Fabian B, Hansen Maike, Rensing Stefan A, Hoecker Ute
Institute for Plant Sciences and Cluster of Excellence on Plant Sciences (CEPLAS), Biocenter, University of Cologne, Zülpicher Strasse 47b, 50674, Cologne, Germany.
Plant Cell Biology, Faculty of Biology, University of Marburg, Karl-von-Frisch-Strasse 8, 35043, Marburg, Germany.
Plant J. 2023 Apr;114(1):159-175. doi: 10.1111/tpj.16128. Epub 2023 Feb 22.
The Arabidopsis COP1/SPA ubiquitin ligase suppresses photomorphogenesis in darkness. In the light, photoreceptors inactivate COP1/SPA to allow a light response. While SPA genes are specific to the green lineage, COP1 also exists in humans. This raises the question of when in evolution plant COP1 acquired the need for SPA accessory proteins. We addressed this question by generating Physcomitrium Ppcop1 mutants and comparing their visible and molecular phenotypes with those of Physcomitrium Ppspa mutants. The phenotype of Ppcop1 nonuple mutants resembles that of Ppspa mutants. Most importantly, both mutants produce green chloroplasts in complete darkness. They also exhibit dwarfed gametophores, disturbed branching of protonemata and absent gravitropism. RNA-sequencing analysis indicates that both mutants undergo weak constitutive light signaling in darkness. PpCOP1 and PpSPA proteins form a complex and they interact via their WD repeat domains with the VP motif of the cryptochrome CCE domain in a blue light-dependent manner. This resembles the interaction of Arabidopsis SPA proteins with Arabidopsis CRY1, and is different from that with Arabidopsis CRY2. Taken together, the data indicate that PpCOP1 and PpSPA act together to regulate growth and development of Physcomitrium. However, in contrast to their Arabidopsis orthologs, PpCOP1 and PpSPA proteins execute only partial suppression of light signaling in darkness. Hence, additional repressors may exist that contribute to the repression of a light response in dark-exposed Physcomitrium.
拟南芥COP1/SPA泛素连接酶在黑暗中抑制光形态建成。在光照条件下，光感受器使COP1/SPA失活，从而引发光反应。虽然SPA基因是绿色植物谱系所特有的，但COP1在人类中也存在。这就引出了一个问题：植物COP1在进化过程中何时开始需要SPA辅助蛋白。我们通过构建小立碗藓Ppcop1突变体，并将其可见表型和分子表型与小立碗藓Ppspa突变体的表型进行比较，来解决这个问题。Ppcop1九倍体突变体的表型与Ppspa突变体相似。最重要的是，这两种突变体在完全黑暗的环境中都能产生绿色叶绿体。它们还表现出配子体矮小、原丝体分支紊乱以及无重力感应现象。RNA测序分析表明，这两种突变体在黑暗中都经历了微弱的组成型光信号传导。PpCOP1和PpSPA蛋白形成复合物，并且它们通过WD重复结构域以蓝光依赖的方式与隐花色素CCE结构域的VP基序相互作用。这类似于拟南芥SPA蛋白与拟南芥CRY1的相互作用，而与拟南芥CRY2的相互作用不同。综上所述，数据表明PpCOP1和PpSPA共同作用来调节小立碗藓的生长和发育。然而，与它们在拟南芥中的直系同源物不同，PpCOP1和PpSPA蛋白在黑暗中仅对光信号传导起到部分抑制作用。因此，可能存在其他阻遏物，它们有助于在黑暗中的小立碗藓中抑制光反应。
