Regulation of auxin response by the protein kinase PINOID

Arabidopsis plants carrying mutations in the PINOID (PID) gene have a pleio tropic shoot phenotype that mimics that of plants grown on auxin transport inhibitors or of plants mutant for the auxin efflux carrier PINFORMED (PIN) , with defects in the formation of cotyledons, flowers, and floral organs. We have cloned PID and find that it is transiently expressed in the embryo and in initiating floral anlagen, demonstrating a specific role for PID in promoting primordium development. Constitutive expression of PID causes a p henotype in both shoots and roots that is similar to that of auxin-insensit ive plants, implying that PID, which encodes a serine-threonine protein kin ase, negatively regulates auxin signaling.