Isolation of a protein interacting with Vfphot1a in guard cells of Vicia faba.

A recent study has demonstrated that phototropins act as blue light receptors in stomatal guard cells. However, the downstream components responsible for phototropin signaling are largely unknown. In this study, using a yeast two-hybrid system, we isolated a Vicia faba protein that has a high similarity to dynein light chain in the C terminus, which interacts with Vicia faba phototropin 1a (Vfphot1a). Protein-blot and two-hybrid analyses revealed that Vfphot1a interacting protein (VfPIP) bound to the N-terminal [corrected] region of Vfphot1a but did not bind to Vfphot1b. The interaction between VfPIP and Vfphot was indicated by a pull-down assay. Northern analysis revealed that the transcription level of VfPIP gene was more abundant in guard cells than in other tissues or cell types. The transiently expressed fusion protein of VfPIP-green fluorescent protein was localized on cortical microtubules in Vicia guard cells. Microtubule-depolymerizing herbicides partially inhibited both blue light-dependent H(+) pumping in Vicia guard cell protoplasts and stomatal opening in the Vicia epidermis. From these results, we conclude that VfPIP may act as a downstream component of phototropin (Vfphot1a) in blue light signaling in guard cells. The possible role of VfPIP in blue light signaling of guard cells is discussed.