A Century of Gibberellin Research

Abstract

Gibberellin research has its origins in Japan in the 19th century, when a disease of rice was shown to be due to a fungal infection. The symptoms of the disease including overgrowth of the seedling and sterility were later shown to be due to secretions of the fungus Gibberella fujikuroi (now reclassified as Fusarium fujikuroi), from which the name gibberellin was derived for the active component. The profound effect of gibberellins on plant growth and development, particularly growth recovery in dwarf mutants and induction of bolting and flowering in some rosette species, prompted speculation that these fungal metabolites were endogenous plant growth regulators and this was confirmed by chemical characterisation in the late 1950s. Gibberellins are now known to be present in vascular plants, and some fungal and bacterial species. The biosynthesis of gibberellins in plants and the fungus has been largely resolved in terms of the pathways, enzymes, genes and their regulation. The proposal that gibberellins act in plants by removing growth limitation was confirmed by the demonstration that they induce the degradation of the growth-inhibiting DELLA proteins. The mechanism by which this is achieved was clarified by the identification of the gibberellin receptor from rice in 2005. Current research on gibberellin action is focussed particularly on the function of DELLA proteins as regulators of gene expression. This review traces the history of gibberellin research with emphasis on the early discoveries that enabled the more recent advances in this field.

Keywords: Evolution; Gibberella fujikuroi; Gibberellin action; Gibberellin biosynthesis; Gibberellin transport.

Fig. 1

Early and intermediate steps of GA biosynthesis in higher plants (green arrows) and the fungus Fusarium fujikuroi (red arrows). In plants, ent-kaurene is synthesised in plastids, predominately via the methylerythritol phosphate pathway, while in fungi, it is biosynthesised from mevalonic acid. Conversion of ent-kaurene to GA₁₂ and GA₅₃ (plants) and GA₁₄ (fungi) is catalysed by membrane-associated cytochrome P450 monooxygenases. Arrows running through structures indicate multiple steps catalysed by single enzymes

Fig. 2

Late steps of GA biosynthesis in vegetative plant tissues (green and brown arrows), pumpkin endosperm (blue arrows) and the fungus Fusarium fujikuroi (red arrows). The main bioactive GAs in plants, GA₁ and GA₄, are boxed in green, while the product of the fungal pathway, GA₃, which is also active and produced as a minor product in some plants, is boxed in red. Brown arrows indicate inactivation of C₁₉-GAs by 2β-hydroxylation and further C-2 oxidation to catabolites (shown for GA₂₉ and GA₅₁, but can also occur for GA₈ and GA₃₄). The reactions are catalysed by soluble 2-oxoglutarate-dependent dioxygenases in plants and cytochrome P450 monooxygenases in the fungus, except for the fungal desaturase that converts GA₄ to GA₇, which is a 2-oxoglutarate-dependent dioxygenase. Arrows running through structures indicate multiple steps catalysed by single enzymes

Fig. 3

Physiological action of GA as illustrated by comparison of the Landsberg erecta Arabidopsis plant with a GA-deficient mutant (ga1-3). In the absence of a GA response stem elongation, leaf enlargement, floral development, seed set and fruit development do not occur

Fig. 4

Representation of GA perception and signal transduction. Binding of a bioactive GA results in a conformational change in the GID1 receptor that promotes interaction with DELLA proteins. Recruitment of an F-box protein initiates ubiquitination of DELLA by an SCF E3 ubiquitin ligase targeting the DELLA for proteasomal degradation. Loss of DELLA relieves growth repression and suppresses other DELLA-mediated responses