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

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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 mutantthylakoid formation 1(thf1), indicating that inactivation or activation of the endogenous G protein α-subunit (GPA1) affects chloroplast development, as does the ectopic expression of the constitutively active Gα-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 inthf1. Furthermore, the ectopic expression ofcGPA1rescues the leaf variegation offtsh2. Consistent with this finding, microarray analysis shows that ectopic expression of cGPA1 partially corrects mis-regulated gene expression inthf1. 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.

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