Extra-large G proteins expand the repertoire of subunits in arabidopsis heterotrimeric G protein signaling

David Chakravorty, Timothy E. Gookin, Matthew J. Milner, Yunqing Yu, Sarah Mary Assmann

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Heterotrimeric G proteins, consisting of Gα, Gβ, and Gγ subunits, are a conserved signal transduction mechanism in eukaryotes. However, G protein subunit numbers in diploid plant genomes are greatly reduced as compared with animals and do not correlate with the diversity of functions and phenotypes in which heterotrimeric G proteins have been implicated. In addition to GPA1, the sole canonical Arabidopsis (Arabidopsis thaliana) Gα subunit, Arabidopsis has three related proteins: the extra-large GTP-binding proteins XLG1, XLG2, and XLG3. We demonstrate that the XLGs can bind Gβγ dimers (AGB1 plus a Gγ subunit: AGG1, AGG2, or AGG3) with differing specificity in yeast (Saccharomyces cerevisiae) three-hybrid assays. Our in silico structural analysis shows that XLG3 aligns closely to the crystal structure of GPA1, and XLG3 also competes with GPA1 for Gβγ binding in yeast. We observed interaction of the XLGs with all three Gβγ dimers at the plasma membrane in planta by bimolecular fluorescence complementation. Bioinformatic and localization studies identified and confirmed nuclear localization signals in XLG2 and XLG3 and a nuclear export signal in XLG3, which may facilitate intracellular shuttling. We found that tunicamycin, salt, and glucose hypersensitivity and increased stomatal density are agb1-specific phenotypes that are not observed in gpa1 mutants but are recapitulated in xlg mutants. Thus, XLG-Gβγ heterotrimers provide additional signaling modalities for tuning plant G protein responses and increase the repertoire of G protein heterotrimer combinations from three to 12. The potential for signal partitioning and competition between the XLGs and GPA1 is a new paradigm for plant-specific cell signaling.

Original languageEnglish (US)
Pages (from-to)512-529
Number of pages18
JournalPlant physiology
Volume169
Issue number1
DOIs
StatePublished - Sep 1 2015

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Heterotrimeric GTP-Binding Proteins
G-proteins
GTP-Binding Proteins
Arabidopsis
Yeasts
Nuclear Export Signals
Plant Genome
Phenotype
Tunicamycin
Nuclear Localization Signals
Plant Proteins
Protein Subunits
Plant Cells
Computational Biology
Eukaryota
Diploidy
Computer Simulation
yeasts
tunicamycin
Saccharomyces cerevisiae

All Science Journal Classification (ASJC) codes

  • Physiology
  • Genetics
  • Plant Science

Cite this

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title = "Extra-large G proteins expand the repertoire of subunits in arabidopsis heterotrimeric G protein signaling",
abstract = "Heterotrimeric G proteins, consisting of Gα, Gβ, and Gγ subunits, are a conserved signal transduction mechanism in eukaryotes. However, G protein subunit numbers in diploid plant genomes are greatly reduced as compared with animals and do not correlate with the diversity of functions and phenotypes in which heterotrimeric G proteins have been implicated. In addition to GPA1, the sole canonical Arabidopsis (Arabidopsis thaliana) Gα subunit, Arabidopsis has three related proteins: the extra-large GTP-binding proteins XLG1, XLG2, and XLG3. We demonstrate that the XLGs can bind Gβγ dimers (AGB1 plus a Gγ subunit: AGG1, AGG2, or AGG3) with differing specificity in yeast (Saccharomyces cerevisiae) three-hybrid assays. Our in silico structural analysis shows that XLG3 aligns closely to the crystal structure of GPA1, and XLG3 also competes with GPA1 for Gβγ binding in yeast. We observed interaction of the XLGs with all three Gβγ dimers at the plasma membrane in planta by bimolecular fluorescence complementation. Bioinformatic and localization studies identified and confirmed nuclear localization signals in XLG2 and XLG3 and a nuclear export signal in XLG3, which may facilitate intracellular shuttling. We found that tunicamycin, salt, and glucose hypersensitivity and increased stomatal density are agb1-specific phenotypes that are not observed in gpa1 mutants but are recapitulated in xlg mutants. Thus, XLG-Gβγ heterotrimers provide additional signaling modalities for tuning plant G protein responses and increase the repertoire of G protein heterotrimer combinations from three to 12. The potential for signal partitioning and competition between the XLGs and GPA1 is a new paradigm for plant-specific cell signaling.",
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Extra-large G proteins expand the repertoire of subunits in arabidopsis heterotrimeric G protein signaling. / Chakravorty, David; Gookin, Timothy E.; Milner, Matthew J.; Yu, Yunqing; Assmann, Sarah Mary.

In: Plant physiology, Vol. 169, No. 1, 01.09.2015, p. 512-529.

Research output: Contribution to journalArticle

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