The Arabidopsis Cupin Domain Protein AtPirin1 Interacts with the G Protein α-Subunit GPA1 and Regulates Seed Germination and Early Seedling Development

Heterotrimeric G proteins are implicated in diverse signaling processes in plants, but the molecular mechanisms of their function are largely unknown. Finding G protein effectors and regulatory proteins can help in understanding the roles of these signal transduction proteins in plants. A yeast two-hybrid screen was performed to search for proteins that interact with Arabidopsis G protein α-subunit (GPA1). One of the identified GPA1-interacting proteins is the cupin-domain protein AtPirin1. Pirin is a recently defined protein found because of its ability to interact with a CCAAT box binding transcription factor. The GPA1–AtPirin1 interaction was confirmed in an in vitro binding assay. We characterized two atpirin1 T-DNA insertional mutants and established that they display a set of phenotypes similar to those of gpa1 mutants, including reduced germination levels in the absence of stratification and an abscisic acid–imposed delay in germination and early seedling development. These data indicate that AtPirin1 likely functions immediately downstream of GPA1 in regulating seed germination and early seedling development.