Plant biology

G Protein Partners

Science's STKE  08 Jul 2003:
Vol. 2003, Issue 190, pp. tw268-TW268
DOI: 10.1126/stke.2003.190.tw268

Unlike animals that have extensive families of G protein subunit genes, plants, such as Arabidopsis, appear to have a much more limited repertoire of G protein subunits. Arabidopsis has a single Gα gene (GPA1), a single Gβ gene, and two Gγ genes. Despite this lack of diversity, GPA1 mutants show several phenotypes consistent with a role in regulating cell division, stomatal aperture regulation, and responsiveness to several plant hormones, as well as sugars. These findings suggest that G proteins participate in several plant signaling pathways. In a yeast two-hybrid screen, Lapik and Kaufman identified Arabidopsis pirin (AtPirin1), which in mammals interacts with a CCAAT box-binding transcription factor, as a partner for GPA1. The promoter of Atpirin1 contained cis elements predicted to confer light and abscisic acid (ABA) regulation to the gene. Indeed, quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed that ABA or low fluence red light stimulated expression of Atpirin1. Analysis of atpirin1 mutants showed that they exhibited similar phenotypes to GPA1 mutants with respect to seed germination, including hypersensitivity to the delaying effects of ABA, consistent with these two proteins participating in seed germination signaling pathways. In vitro, the interaction between AtPirin1 and GPA1 was not dependent on the activation state of GPA1. AtPirin1 appears also to participate in GPA1-independent pathways, because atpirin1 mutants exhibited accelerated flowering rate, which is not a phenotype of the GPA1 mutants. It remains to be determined how GPA1 and AtPirin1 participate and interact during plant signaling.

Y. R. Lapik, L. S. Kaufman, The Arabidopsis cupin domain protein AtPirin1 interacts with G protein α-subunit GPA1 and regulates seed germination and early seedling development. Plant Cell 15, 1578-1590 (2003). [Abstract] [Full Text]