Donald Danforth Plant Science Center, St. Louis, MO 63132.
Department of Biology, Washington University in St. Louis, St. Louis, MO 63130.
Proc Natl Acad Sci U S A. 2019 Apr 23;116(17):8603-8608. doi: 10.1073/pnas.1818217116. Epub 2019 Apr 4.
The members of the phytochrome (phy) family of bilin-containing photoreceptors are major regulators of plant photomorphogenesis through their unique ability to photointerconvert between a biologically inactive red light-absorbing Pr state and an active far-red light-absorbing Pfr state. While the initial steps in Pfr signaling are unclear, an early event for the phyB isoform after photoconversion is its redistribution from the cytoplasm into subnuclear foci known as photobodies (PBs), which dissipate after Pfr reverts back to Pr by far-red irradiation or by temperature-dependent nonphotochemical reversion. Here we present evidence that PHOTOPERIODIC CONTROL OF HYPOCOTYL 1 (PCH1) functions both as an essential structural component of phyB-containing PBs and as a direct regulator of thermal reversion that is sufficient to stabilize phyB as Pfr in vitro. By examining the genetic interaction between a constitutively active phyB-YFP allele () and PCH1, we show that the loss of PCH1 prevents YHB from coalescing into PBs without affecting its nuclear localization, whereas overexpression of PCH1 dramatically increases PB levels. Loss of PCH1, presumably by impacting phyB-PB assembly, compromises a number of events elicited in plants, including their constitutive photomorphogenic phenotype, red light-regulated thermomorphogenesis, and input of phyB into the circadian clock. Conversely, elevated levels of both phyB and PCH1 generate stable, yet far-red light-reversible PBs that persisted for days. Collectively, our data demonstrate that the assembly of PCH1-containing PBs is critical for phyB signaling to multiple outputs and suggest that altering PB dynamics could be exploited to modulate plant responses to light and temperature.
植物光受体中的光敏色素（phy）家族成员通过其独特的能力在生物活性较弱的红光吸收 Pr 态和活性远红光吸收 Pfr 态之间进行光互变，成为植物光形态建成的主要调控因子。虽然 Pfr 信号的初始步骤尚不清楚，但 phyB 同工型在光转化后发生的早期事件是其从细胞质重新分布到亚核焦点，称为光体（PBs），当 Pfr 通过远红光照射或温度依赖的非光化学回复回到 Pr 时，PBs 会消失。在这里，我们提供的证据表明，光周期调控下胚轴 1（PCH1）既是含 phyB 的 PB 的必需结构组成部分，也是热回复的直接调控因子，足以在体外稳定 phyB 作为 Pfr。通过检查组成型活性 phyB-YFP 等位基因（）和 PCH1 之间的遗传相互作用，我们表明 PCH1 的缺失阻止了 YHB 聚集成 PB，而不影响其核定位，而 PCH1 的过表达则显著增加了 PB 的水平。PCH1 的缺失，大概是通过影响 phyB-PB 组装，损害了许多在植物中引发的事件，包括其组成型光形态建成表型、红光调节的热形态建成以及 phyB 对生物钟的输入。相反，phyB 和 PCH1 水平的升高会产生稳定的、但可被远红光逆转的 PB，这些 PB 可以持续数天。总的来说，我们的数据表明，含有 PCH1 的 PB 的组装对于 phyB 信号向多个输出是至关重要的，并表明改变 PB 动力学可以用来调节植物对光和温度的反应。
