In many plant species, roots maintain specific growth angles relative to the direction of gravity, known as gravitropic set point angles (GSA). These contribute to the efficient acquisition of water and nutrients. AtLAZY1/LAZY1-LIKE (LZY) genes are involved in GSA control by regulating auxin flow toward the direction of gravity in Arabidopsis. LZYs are plant-specific unknown proteins with no domain for which the function is inferable. To clarify the molecular function of LZYs, we identified the proteins that interact with them by immunoprecipitation coupled with mass spectrometry.