Abstract
The three-member family of Arabidopsis extra-large G proteins (XLG1-3) defines the prototype of an atypical Gα subunit in the heterotrimeric G protein complex. Recent evidence indicate that XLG subunits operate along with its Gβγ dimer in root morphology, stress responsiveness, and cytokinin induced development, however downstream targets of activated XLG proteins in the stress pathways are rarely known. To assemble a set of candidate XLG-targeted proteins, a yeast two-hybrid complementation-based screen was performed using XLG protein baits to query interactions between XLG and partner protein found in glucose-treated seedlings, roots, and Arabidopsis cells in culture. Seventy two interactors were identified and >60% of a test set displayed in vivo interaction with XLG proteins. Gene co-expression analysis shows that >70% of the interactors are positively correlated with the corresponding XLG partners. Gene Ontology enrichment for all the candidates indicates stress responses and posits a molecular mechanism involving a specific set of transcription factor partners to XLG. Genes encoding two of these transcription factors, SZF1 and 2, require XLG proteins for full NaCl-induced expression. The subcellular localization of the XLG proteins in the nucleus, endosome, and plasma membrane is dependent on the specific interacting partner.
Highlights
In animals, the heterotrimeric G protein complex consists of Gα, Gβ, and Gγ subunits and is tethered to the cytoplasmic side of the plasma membrane nestled with 7 transmembrane (Hamm, 1998; Oldham and Hamm, 2008)
Our work provides a large set of stress-related proteins for future studies to test mechanism
We also provide an explanation of the conflicting reports on XLG subcellular localization by showing that the localization of the XLGs is dependent on the specific interacting partner
Summary
The heterotrimeric G protein complex consists of Gα, Gβ, and Gγ subunits and is tethered to the cytoplasmic side of the plasma membrane nestled with 7 transmembrane (Hamm, 1998; Oldham and Hamm, 2008). GPCRs receive extracellular signals and activate the G protein signaling pathway by catalyzing GDP removal from the Gα subunit allowing GTP binding and subsequent release of the Gβγ dimer (Wettschureck, 2005; Li et al, 2007; Oldham and Hamm, 2008). Regulator of G Signaling (RGS) proteins accelerate GTP hydrolysis. The human genome encodes 23 Gα, 5 Gβ, and 12 Gγ subunits, ∼850 GPCRs, and ∼40 RGS proteins. In Arabidopsis, the heterotrimeric G protein complex consist
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