Here we describe a series TAP-MS analyses in various mutant backgrounds of Arabidopsis thaliana to co-purify any PCH1’s associated proteins, using tagged PCH1 as bait (PCH1-His6-Flag3, either overexpressed or under the control of its own promoter). By combining TAP-MS with genetics, we investigate the in-vivo dependence of several proteins for maintaining the association of PCH1 with its interacting proteins. Our results refine the protein-protein interaction network of an existing interactome containing phytochromes, the COP1-SPAs complex and the ELF3-ELF4-LUX complex.