Activation of the heterotrimeric G protein alpha-subunit GPA1 suppresses the ftsh-mediated inhibition of chloroplast development in Arabidopsis.

Heterotrimeric G protein knock-out mutants have no phenotypic defect in chloroplast development, and the connection between the G protein signaling pathway and chloroplast development has only been inferred from pharmaceutical evidence. Thus, whether G protein signaling plays a role in chloroplast development remains an open question. Here, we present genetic evidence, using the leaf-variegated mutant thylakoid formation 1 (thf1), indicating that inactivation or activation of the endogenous G protein alpha-subunit (GPA1) affects chloroplast development, as does the ectopic expression of the constitutively active Galpha-subunit (cGPA1). Molecular biological and genetic analyses showed that FtsH complexes, which are composed of type-A (FtsH1/FtsH5) and type-B (FtsH2/FtsH8) subunits, are required for cGPA1-promoted chloroplast development in thf1. Furthermore, the ectopic expression of cGPA1 rescues the leaf variegation of ftsh2. Consistent with this finding, microarray analysis shows that ectopic expression of cGPA1 partially corrects mis-regulated gene expression in thf1. This overlooked function of G proteins provides new insight into our understanding of the integrative signaling network, which dynamically regulates chloroplast development and function in response to both intracellular and extracellular signals.