Phytochrome cytoplasmic signalling in lower plants

光敏色素光感受器在植物的光调控发育中起着核心作用。在它们的Pr基态下，植物光敏色素通常是细胞质的，但红光吸收诱导了Pfr信号状态，其中一部分随后被转运到细胞核中调节转录。然而，一些光敏色素的作用太快，转录变化不参与。此外，低等植物中的光敏色素为单个细胞的定向生长和叶绿体的重新定位提供了载体信息：这不能基于转录调节。因此光敏色素在细胞质内一定有另一种信号传导机制。我们现在已经确定并初步描述了这是由小立壶菌质膜上光敏色素分子亚群与趋光素的迄今为止意想不到的相互作用引起的（Jaedicke et al. (2012) PNAS）。本项目的目的是在分子水平上描述该复合体及其信号传导机制。为此，我们将借助分子遗传学、细胞生物学、生物化学和生物物理学的方法，从生理学（光向性和极向性）和遗传学（基因组序列和同源重组）两方面对小壶藻模型系统进行开发。我们建议继续使用多种酵母双杂交方法来鉴定潜在的细胞质光敏色素相互作用，并通过双分子荧光互补、荧光寿命成像、共免疫沉淀、靶向敲除/互补等技术来表征相关的信号系统。虽然我们有证据表明，在拟南芥中也发生了物理-光相互作用，但我们不打算在本应用中对此进行研究。

Phytochrome photoreceptors play a central role in light-regulated development in plants. In their Pr ground state plant phytochromes are generally cytosolic but red light absorption induces the Pfr signalling state, a proportion of which is then transported into the nucleus to regulate transcription. However, some phytochrome effects are too fast for transcriptional changes to be involved. Also phytochrome in lower plants provides vectorial information for directional growth of individual cells and chloroplast relocation: this cannot be based on transcription regulation. Thus phytochrome must have another signalling mechanism within the cytoplasm. We have now identified and initially characterized this as arising from a hitherto unexpected interaction of a sub-population of phytochrome molecules with phototropin at the plasma membrane in Physcomitrella (Jaedicke et al. (2012) PNAS). The purpose of this project is to describe the complex and its signaling mechanism at the molecular level. To this end we will exploit the Physcomitrella model system physiologically (photo- and polarotropism) and genetically (genome sequence and homologous recombination) with the help of molecular genetic, cell biological, biochemical and biophysical methods. We propose to continue our work using a variety of yeast two-hybrid approaches to identify potential cytoplasmic phytochrome interactors and to characterize the associated signaling system by bimolecular fluorescence complementation, fluorescence lifetime imaging, co-immunoprecipitation, targetted knockout / complementation and other techniques. Although we have evidence that the phy-phot interaction occurs in Arabidopsis too, we do not propose to study this in the present application.