Extragenic Suppressors of the Arabidopsis gaiMutation Alter the Dose-Response Relationship of Diverse Gibberellin Responses1

Abstract

Active gibberellins (GAs) are endogenous factors that regulate plant growth and development in a dose-dependent fashion. Mutant plants that are GA deficient, or exhibit reduced GA responses, display a characteristic dwarf phenotype. Extragenic suppressor analysis has resulted in the isolation of Arabidopsis mutations, which partially suppress the dwarf phenotype conferred by GA deficiency and reduced GA-response mutations. Here we describe detailed studies of the effects of two of these suppressors, spy-7 and gar2-1, on several different GA-responsive growth processes (seed germination, vegetative growth, stem elongation, chlorophyll accumulation, and flowering) and on the in planta amounts of active and inactive GA species. The results of these experiments show that spy-7 and gar2-1 affect the GA dose-response relationship for a wide range of GA responses and suggest that all GA-regulated processes are controlled through a negatively acting GA-signaling pathway.

The Arabidopsis Mutant sleepy1gar2-1 Protein Promotes Plant Growth by Increasing the Affinity of the SCFSLY1 E3 Ubiquitin Ligase for DELLA Protein Substrates[W]

“…Although gar2-1 was known to suppress gai phenotype (Wilson and Somerville, 1995;Peng et al, 1997Peng et al, , 1999b, it was not clear how gar2-1 affected the properties of the gai protein. We therefore further investigated the effect of gar2-1 on gai.…”

“…However, 35S:SLY1 conferred increased resistance to PAC, a GA biosynthesis inhibitor (Hedden and Graebe, 1985;Davis and Curry, 1991). 35S:SLY1 seeds germinated on PAC-containing medium (as did positive control gai sly1 gar2-1 seeds; Peng et al, 1999b), whereas the germination of wild-type control seeds was substantially inhibited ( Figure 4C). Furthermore, 35S:SLY1 suppressed the dwarf phenotype conferred by the GA-deficiency (B) GAI-GFP fluorescence in pGAI:GAI-GFP or sly1-10 pGAI:GAI-GFP primary roots treated (or control) with 100 mM GA 3 .…”

“…In addition, these screens led to the identification of extragenic suppressors, mutations in genes other than GAI itself, which cause suppression of the dwarf phenotype conferred by gai (Carol et al, 1995;Wilson and Somerville, 1995). One such extragenic suppressor mutation was gai revertant2-1 (gar2-1), a dominant extragenic suppressor of gai phenotype (Wilson and Somerville, 1995;Peng et al, 1997Peng et al, , 1999b. gar2-1 confers resistance to the GA biosynthesis inhibitor paclobutrazol (PAC) and acts additively with loss-of-function alleles of SPINDLY (a gene encoding an O-GlcNAc transferase with GA-signaling function; Jacobsen et al, 1996;Swain et al, 2002) in suppressing gai phenotype (Wilson and Somerville, 1995;Peng et al, 1997Peng et al, , 1999b.…”

“…One such extragenic suppressor mutation was gai revertant2-1 (gar2-1), a dominant extragenic suppressor of gai phenotype (Wilson and Somerville, 1995;Peng et al, 1997Peng et al, , 1999b. gar2-1 confers resistance to the GA biosynthesis inhibitor paclobutrazol (PAC) and acts additively with loss-of-function alleles of SPINDLY (a gene encoding an O-GlcNAc transferase with GA-signaling function; Jacobsen et al, 1996;Swain et al, 2002) in suppressing gai phenotype (Wilson and Somerville, 1995;Peng et al, 1997Peng et al, , 1999b. In addition, recent results show that gar2-1 increases the growth of GA-deficient pollen tubes (Swain et al, 2004).…”

Cloning and Overproduction of Gibberellin 3-Oxidase in Hybrid Aspen Trees. Effects on Gibberellin Homeostasis and Development

“…Furthermore, evidence for interactions between GA signaling and biosynthesis has come from studies of GA signaling mutants. For instance, the gai mutant has increased levels of bioactive GAs and GA20ox transcript (Peng et al, 1999). As a result of the feedback and feed-forward regulation, governed by the endogenous levels of GA 1 and GA 4 , the plant can maintain appropriate levels of GAs throughout its growth and development.…”