Phytochrome C and Low Temperature Promote the Expression and Red Light Signaling of Phytochrome D

Light is an ever-changing environmental parameter affecting almost every aspects of plant growth and development. It is perceived by photoreceptors, among them phytochromes (PHY) are responsible for monitoring the red and far-red part of the spectrum. Arabidopsis thaliana possesses five phytochromes genes, named through phyA-phyE. Whereas the function of phyA and phyB – that mediate most of the phytochrome responses – is extensively studied, our knowledge on other phytochromes are still rudimentary. To analyze phyD function we expressed it at high levels in different phytochrome deficient genetic backgrounds. We found that overexpressed phyD governs effective light signaling at low temperatures but only in cooperation with functional phyC. Under these conditions, opposite to phyB, phyD accumulates to high levels and this pool is stable under light illumination. Furthermore, the detectable photoconvertible phyD amount is proportional with the available protein amount indicating that the phyD pool contains fully functional photoreceptors. The thermal reversion of phyD is very fast suggesting that the thermosensing of phyD is based on its protein amount and not on its Pfr conformer stability, which was described for phyB. We also found that phyD and phyB associate to identical genomic locations and mediate similar gene expression changes, however the efficiency of phyD is lower. Taken together our data suggest that under certain conditions synergistic interaction of phyD and phyC substitutes phyB function thus increases the ability of plants to respond more flexible to environmental changes. Overall design: Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) with anti-GFP antibody that recognise PHYD-YFP and PHYB-GFP transgenic protein.

光是一种持续变化的环境参数，几乎影响植物生长与发育的所有环节。植物通过光受体感知光信号，其中光敏色素（phytochromes, PHY）负责监测光谱中的红光与远红光波段。拟南芥（Arabidopsis thaliana）拥有5个光敏色素基因，依次命名为phyA至phyE。尽管介导绝大多数光敏色素响应的phyA和phyB的功能已被广泛研究，但我们对其他光敏色素的认知仍较为粗浅。为解析phyD的功能，我们在不同光敏色素缺陷型遗传背景中对其进行过表达。研究发现，过表达的phyD仅在与功能完整的phyC协同作用时，方可在低温条件下介导有效的光信号通路。在此条件下，与phyB截然相反，phyD会积累至较高水平，且该蛋白池在光照环境下保持稳定。此外，可检测到的光可逆转换型phyD的含量与可用蛋白总量呈正相关，这表明phyD蛋白池包含完全具备功能的光敏色素。phyD的热逆转速率极快，这提示phyD的温度感知机制依赖于其蛋白含量，而非此前在phyB中所报道的Pfr构象稳定性。我们还发现，phyD与phyB能够结合至相同的基因组位点，并介导相似的基因表达变化，不过phyD的作用效率更低。综合本研究所有数据，我们认为在特定条件下，phyD与phyC的协同互作可替代phyB的功能，从而提升植物对环境变化做出更灵活响应的能力。实验整体设计：使用可识别PHYD-YFP与PHYB-GFP融合转基因蛋白的抗GFP抗体，开展染色质免疫共沉淀测序（Chromatin immunoprecipitation DNA-sequencing, ChIP-seq）实验。