Abstract
In light signaling pathways, protein complexes play essential roles in light perception and signal transduction. The phytochrome family of photoreceptors perceives red/far-red region of the light spectrum and then translocates into the nucleus to form protein complexes. Many phytochrome interacting proteins have been identified based on yeast two-hybrid screening and other protein-protein interaction methods. However, it is essential to demonstrate that these proteins interact with phytochromes in vivo to be functionally relevant. In this chapter, a protocol for demonstrating light dependent in vivo interactions between phytochromes and phytochrome interacting proteins is described. This protocol can be adapted for any putative phytochrome interacting protein for validation of their interaction in vivo.