| Summary: | Heterotrimeric G proteins are the molecule switch that transmits information from external signals to intracellular target proteins in mammals and yeast cells. In higher plants, heterotrimeric G proteins regulate plant architecture. Rice harbors one canonical α subunit gene (<i>RGA1</i>), four extra-large GTP-binding protein genes (XLGs), one canonical β-subunit gene (<i>RGB1</i>), and five γ-subunit genes (tentatively designated <i>RGG1</i>, <i>RGG2</i>, <i>RGG3</i>/<i>GS3</i>/<i>Mi</i>/<i>OsGGC1</i>, <i>RGG4</i>/<i>DEP1</i>/<i>DN1</i>/<i>qPE9-1</i>/<i>OsGGC3</i>, and <i>RGG5</i>/<i>OsGGC2</i>) as components of the heterotrimeric G protein complex. Among the five γ-subunit genes, <i>RGG1</i> encodes the canonical γ-subunit, <i>RGG2</i> encodes a plant-specific type of γ-subunit with additional amino acid residues at the N-terminus, and the remaining three γ-subunit genes encode atypical γ-subunits with cysteine-rich C-termini. We characterized the <i>RGG4</i>/<i>DEP1</i>/<i>DN1</i>/<i>qPE9-1</i>/<i>OsGGC3</i> gene product Gγ4 in the wild type (WT) and truncated protein Gγ4∆Cys in the <i>RGG4</i>/<i>DEP1</i>/<i>DN1</i>/<i>qPE9-1</i>/<i>OsGGC3</i> mutant, <i>Dn1-1</i>, as littele information regarding the native Gγ4 and Gγ4∆Cys proteins is currently available. Based on liquid chromatography-tandem mass spectrometry analysis, immunoprecipitated Gγ4 candidates were confirmed as actual Gγ4. Similar to α-(Gα) and β-subunits (Gβ), Gγ4 was enriched in the plasma membrane fraction and accumulated in the developing leaf sheath. As <i>RGG4</i>/<i>DEP1</i>/<i>DN1</i>/<i>qPE9-1</i>/<i>OsGGC3</i> mutants exhibited dwarfism, tissues that accumulated Gγ4 corresponded to the abnormal tissues observed in <i>RGG4</i>/<i>DEP1</i>/<i>DN1</i>/<i>qPE9-1</i>/<i>OsGGC3</i> mutants.
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