The Arabidopsis GAI gene defines a signaling pathway that negatively regulates gibberellin responses

Abstract

The Arabidopsis gai mutant allele confers a reduction in gibberellin (GA) responsiveness. Here we report the molecular cloning of GAI and a closely related gene GRS. The predicted GAI (wild-type) and gai (mutant) proteins differ only by the deletion of a 17-amino-acid segment from within the amino-terminal region. GAI and GRS contain nuclear localization signals, a region of homology to a putative transcription factor, and motifs characteristic of transcriptional coactivators. Genetic analysis indicates that GAI is a repressor of GA responses, that GA can release this repression, and that gai is a mutant repressor that is relatively resistant to the effects of GA. Mutations at SPY and GAR2 suppress the gai phenotype, indicating the involvement of GAI, SPY, and GAR2 in a signaling pathway that regulates GA responses negatively. The existence of this pathway suggests that GA modulates plant growth through derepression rather than through simple stimulation.

Large-scale analysis of the GRAS gene family in Arabidopsis thaliana

“…SHR, SCL29, and SCL32 belong to the branch III, and only SHR has been analyzed in detail (Helariutta et al 2000;Nakajima et al 2001). The branch IV comprises so-called ''DELLA'' proteins: GAI, RGA, RGL1, RGL2, and RGL3, which are negative regulators of GA signaling (Peng et al 1997;Silverstone et al 1998;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Tyler et al 2004). LAS, SCR, and SCL23 appear to belong to the branch V, but only the robustness of node for SCR and SCL23 is strongly supported in our bootstrap analysis ( Supplementary Fig.…”

“…1a). Of 33 GRAS genes, only a third was genetically analyzed: GAI, RGA, RGL1, RGL2, RGL3, SCR, SHR, PAT1, SCL13, and SCL18/ LAS (Di Laurenzio et al 1996;Peng et al 1997;Silverstone et al 1998;Bolle et al 2000;Helariutta et al 2000;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Greb et al 2003;Tyler et al 2004;Torres-Galea et al 2006). Typically, GRAS proteins share signature motifs of VHIID flanked by two leucine heptad repeats (LHRI and LHRII), PFYRE and SAW (designated after the profound amino acid residues in the conserved regions) with rather variable N-terminal regions (Pysh et al 1999;Bolle 2004).…”

“…GRAS proteins belong to a plant specific transcription factor family, named after the three founding members, GIBBERELLIC ACID INSENSITIVE (G AI), REPRESSOR OF GA1 (R G A), and SCARECROW (S CR) (Di Laurenzio et al 1996;Peng et al 1997;Silverstone et al 1998;Pysh et al 1999;Bolle 2004). Typically, GRAS proteins consist of variable N-terminal region, VHIID flanked by two leucine heptad repeats (LHRI and LHRII), PFYRE, and SAW motifs (Pysh et al 1999;Bolle 2004).…”

“…According to the current genome annotation (version 7.0), a total of 33 GRAS genes are predicted in Arabidopsis thaliana (TAIR, http://www.arabidopsis.org). Of them, only 10 GRAS genes were analyzed in detail thus far: GAI, RGA, RGL1, RGL2, RGL3, SCR, SHR, PAT1, SCL13, and SCL18/LAS (Di Laurenzio et al 1996;Peng et al 1997;Silverstone et al 1998;Bolle et al 2000;Helariutta et al 2000;Dill and Sun 2001;Lee et al 2002;Wen and Chang 2002;Greb et al 2003;Tyler et al 2004;Torres-Galea et al 2006). These genes play a crucial role in diverse plant growth and development, ranging from GA signaling, root radial pattering, light signal transduction, and axillary shoot meristem formation.…”

The phenotypic expression of QTLs for partial resistance to barley leaf rust during plant development

“…Phytohormones, which are growth regulators, are involved in plant development as well as in defense pathways (Whalen 2005;Develey-Rivière and Galiana 2007;Bari and Jones 2009). Gibberellins (GAs), promote seed germination and stem elongation (Poethig 2003;Bäurle and Dean 2006) by stimulating the degradation of negative regulators called DELLA proteins (Peng et al 1997(Peng et al , 1999. Recently, DELLA proteins have been regarded as integrators and regulators of plant defense pathways (Navarro et al 2008;Grant and Jones 2009;Peng 2009).…”