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The Plant Cell, Vol. 15, 151163, January 2003, www.plantcell.org 2002 American Society of Plant Biologists Overexpression of a Novel Class of Gibberellin 2-Oxidases
 

Summary: The Plant Cell, Vol. 15, 151­163, January 2003, www.plantcell.org © 2002 American Society of Plant Biologists
Overexpression of a Novel Class of Gibberellin 2-Oxidases
Decreases Gibberellin Levels and Creates Dwarf Plants
Fritz M. Schomburg,a,1 Colleen M. Bizzell,a,1 Dong Ju Lee,b Jan A. D. Zeevaart,b,c,2 and Richard M. Amasinoa,2
a Department of Biochemistry, University of Wisconsin­Madison, Madison, Wisconsin 53706
b Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824-1312
c Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824-1312
Degradation of active C19-gibberellins (GAs) by dioxygenases through 2 -hydroxylation yields inactive GA products. We
identified two genes in Arabidopsis (AtGA2ox7 and AtGA2ox8), using an activation-tagging mutant screen, that encode
2 -hydroxylases. GA levels in both activation-tagged lines were reduced significantly, and the lines displayed dwarf
phenotypes typical of mutants with a GA deficiency. Increased expression of either AtGA2ox7 or AtGA2ox8 also caused
a dwarf phenotype in tobacco, indicating that the substrates for these enzymes are conserved. AtGA2ox7 and
AtGA2ox8 are more similar to each other than to other proteins encoded in the Arabidopsis genome, indicating that
they may constitute a separate class of GA-modifying enzymes. Indeed, enzymatic assays demonstrated that
AtGA2ox7 and AtGA2ox8 both perform the same GA modification: 2 -hydroxylation of C20-GAs but not of C19-GAs.
Lines containing increased expression of AtGA2ox8 exhibited a GA dose­response curve for stem elongation similar to
that of the biosynthetic mutant ga1-11. Double loss-of-function Atga2ox7 Atga2ox8 mutants had twofold to fourfold
higher levels of active GAs and displayed phenotypes associated with excess GAs, such as early bolting in short days,
resistance to the GA biosynthesis inhibitor ancymidol, and decreased mRNA levels of AtGA20ox1, a gene in the GA bio-
synthetic pathway.

  

Source: Amasino, Richard M. - Department of Biochemistry, University of Wisconsin at Madison

 

Collections: Biology and Medicine