Abstract
Phytochromes are red/far-red light receptors that perceive and transduce light signals to regulate various physiological responses. A large number of phytochrome interacting proteins have been identified using genetic and biochemical approaches. A direct interaction between phytochrome and its interacting proteins, therefore, defines one of the critical steps to initiate light signaling cascades in plants. Thus it is important to thoroughly examine the light-dependent interaction between phytochromes and putative phytochrome-interacting proteins. In this chapter, a protocol for rapid and simple light dependent in vitro coimmunoprecipitation between phytochromes and phytochrome interacting factors is described. In principle, this protocol can be adapted for other putative phytochrome interacting proteins.