PMID:17894782

Citation	Gao, Y, Zeng, Q, Guo, J, Cheng, J, Ellis, BE and Chen, JG (2007) Genetic characterization reveals no role for the reported ABA receptor, GCR2, in ABA control of seed germination and early seedling development in Arabidopsis. Plant J. 52:1001-13
Abstract	Abscisic acid (ABA) is perceived by several different types of receptors in plant cells. At the cell surface, the ABA signal is proposed to be perceived by GCR2, which mediates ABA responses in seed germination, early seedling development and stomatal movement. GCR2 was also proposed to be a seven-transmembrane (7TM) G-protein-coupled receptor (GPCR). Here we characterize GCR2 and one of its two homologs, GCR2-LIKE 1 (GCL1), in ABA-mediated seed germination and early seedling development in Arabidopsis. We show that loss-of-function mutations in GCL1 did not confer ABA insensitivity. Similarly, we did not observe ABA insensitivity in three independent gcr2 alleles. Furthermore, we generated gcr2 gcl1 double mutants and found that the double mutants still had near wild-type responses to ABA. Consistent with this, we found that the transcription of ABA marker genes was induced by ABA to levels that were comparable in wild type and gcr2 and gcl1 single and double mutants. On the other hand, the loss-of-function alleles of the sole Arabidopsis heterotrimeric G protein alpha subunit, GPA1, were hypersensitive to ABA in the ABA-inhibition of seed germination and early seedling development, disfavoring a genetic coupling of GCR2 by GPA1. Using multiple robust transmembrane prediction systems, GCR2 was predicted not to be a 7TM protein, a structural hallmark of GPCRs. Taken together, our results do not support the notion that GCR2 is an ABA-signaling GPCR in seed germination and early seedling development.
Links	PubMed Online version:10.1111/j.1365-313X.2007.03291.x
Keywords	Abscisic Acid/pharmacology; Alleles; Amino Acid Sequence; Arabidopsis/drug effects; Arabidopsis/genetics; Arabidopsis/growth & development; Arabidopsis Proteins/genetics; Arabidopsis Proteins/physiology; GTP-Binding Protein alpha Subunits/genetics; GTP-Binding Protein alpha Subunits/physiology; Gene Expression Regulation, Plant/drug effects; Germination/drug effects; Germination/genetics; Germination/physiology; Molecular Sequence Data; Mutation; Plant Growth Regulators/pharmacology; Receptors, G-Protein-Coupled/genetics; Receptors, G-Protein-Coupled/physiology; Reverse Transcriptase Polymerase Chain Reaction; Seedling/drug effects; Seedling/genetics; Seedling/growth & development; Seeds/drug effects; Seeds/genetics; Seeds/growth & development; Sequence Homology, Amino Acid; Transcription, Genetic/drug effects
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