Isolation of the Arabidopsis GA4 locus.

Abstract

Progeny from a transgenic Arabidopsis plant generated by the Agrobacterium root transformation procedure were found to segregate for a gibberellin (GA)-responsive semidwarf phenotype. Complementation analysis with genetically characterized GA-responsive mutants revealed that the transgenic plant has an insertional mutation (ga4-2) that is an allele of the ga4 locus. The semidwarf phenotype of ga4-2 is inherited as a recessive mutation that cosegregates with both the T-DNA insert and the kanamycin resistance trait. DNA gel blot analysis indicated that the insertion site contains a complex T-DNA unit. A genomic library was constructed with DNA from the tagged ga4 mutant; a DNA clone was isolated from the library that flanks the T-DNA insert. The plant sequence isolated from this clone was used to isolate the corresponding full-length genomic and cDNA clones from wild-type libraries. DNA sequence comparison of the clones to the existing data bases suggests that they encode a hydroxylase. This conclusion is in agreement with a biochemical study that indicated that the ga4 mutant is deficient in 3P-hydroxylase in the GA biosynthetic pathway of Arabidopsis. FINA gel blot analysis showed that the message is ubiquitously expressed in different tissues of Arabidopsis but most abundantly in the silique. Unexpectedly, a higher leve1 of transcription was detected i n the ethyl methanesulfonate-induced ga4 mutant, and this overexpression was repressed by treatment with exogenous GA.

Gibberellin A1 Metabolism Contributes to the Control of Photoperiod-Mediated Tuberization in Potato

“…The recombinant product of StGA3ox2 is a functional enzyme catalyzing the conversion of both 3 H-GA 20 and 14 C-GA 9 into 3 H-GA 1 and 14 C-GA 4 , respectively (Figure 3B). This agrees with pea PsGA3ox1 and Arabidopsis AtGA3ox2 genes encoding GA 3-oxidase proteins catalyzing the synthesis of active GAs both in the early- and non-C13-hydroxylation pathways [30], [31], [32]. The higher StGA3ox2 expression in the shoots of the 35S:3ox2 and LS1:3ox2 transgenic plants resulted in lower levels of GA 20 (the substrate) and higher levels of GA 1 (the product) than in control plants (Table 1), demonstrating that StGA3ox2 encodes an enzyme with GA 3-oxidase activity also in planta .…”

Arabidopsis CBF3 and DELLAs positively regulate each other in response to low temperature

“…GA 20-oxidases (GA20ox) and GA 3-oxidases (GA3ox) catalyze successive steps in the synthesis of bioactive GAs27, while GA 2-oxidases (GA2ox) deactivate bioactive GAs29. To further figure out the mechanism involved in GA decrease and DELLA increase, we tested the expression pattern of GA signaling and metabolic genes in CBF1-ox, CBF2-ox and CBF3-ox plants.…”

“…Bioactive GAs promote plant cell elongation2425 and are synthesized with the activities of GA20-oxidases26 and GA3-oxidases2728, but reduced by GA2-oxidases29. Bioactive GAs can bind to the Gibberellin Insensitive Dwarf1 (GID1) receptor, and the GA-GID1 complex together with the SCF SLY1 E3 ligase facilitate ubiquitination of DELLA proteins and their subsequent degradation by the 26S proteasome3031.…”

The bHLH transcription factor SPATULA regulates root growth by controlling the size of the root meristem

“…GA20-oxidases and GA3-oxidases are each encoded by multi-gene families and catalyze the final steps in GA biosynthesis pathway [46]. These genes are expressed at higher levels in GA-deficient backgrounds and their expression decreases after application of bioactive GAs [47-51]. Endogenous GA levels are regulated by metabolic deactivation and the GA2-oxidases are the best characterized enzymes shown to catalyze such a reaction [51,52].…”