Subcellular localization of G3BP6 regulates flowering in Arabidopsis

Ras GTPase-Activating Protein SH3 Domain-Binding Protein (G3BP) belongs to the highly conserved family of RNA-binding proteins, which are well investigated to participate in the formation of stress granules (SG) in humans and animals. However, limited study on plant G3BP has been reported and the precise biological function of G3BP family has not been elucidated yet. In this study, 7 Arabidopsis G3BPs were comparatively analyzed. Transcriptome analysis showed that the most G3BP genes are ubiquitously expressed in various tissues/organs. Transient expression analysis revealed that all G3BP proteins presented in plasm brane or cytosol, while G3BP6 is additionally found in the nucleus. Phenotypic analysis revealed that loss-of-function g3bp6 presented strong late flowering phenotype. Transcriptome analysis and qRT-PCR assays demonstrated that a series of genes tightly related to flowering were significantly altered in g3bp6. Further study with truncated G3BP6 proteins revealed a short conserved motif required for nuclear localization. Moreover, we found that overexpression of the nuclear other than cytoplasmic G3BP6 promoted flowering. In addition, we revealed that scaffold protein RACK1 interacts with G3BP6 and modulates the nuclear localization of G3BP6. Collectively, this study reveals a specific role of G3BP6 protein from Arabidopsis in plant flowering, which provides new knowledge of G3BP proteins in plants.