Gibberellin Biosynthesis

Abstract

The gibberellins are a large class of tetracyclic diterpenoid carboxylic acids, which are present in flowering plants, as well as some species of lower plants, fungi and bacteria. They include endogenous growth regulators in higher plants, in which they promote organ growth and induce certain developmental switches. Production of the biologically active compounds in plants requires the activity of plastid‐localised terpene cyclases, membrane‐associated cytochrome P450 monooxygenases and soluble 2‐oxoglutarate‐dependent dioxygenases. In most plant tissues the concentrations of the active compounds are tightly regulated, in a process that requires their turnover through deactivation, for which several mechanisms have been identified, including 2β‐hydroxylation. Regulation of gibberellin concentration occurs in response to environmental cues, such as light quality, temperature and stress, as well as developmental and hormonal signals. Furthermore, gibberellin biosynthesis and inactivation are subject to homoeostasis mechanisms that act through the gibberellin signalling pathway.

Key Concepts:

  • Gibberellins are a group of tetracyclic diterpenoid carboxylic acids, which includes endogenous plant growth factors.

  • The biosynthesis of gibberellins requires the action of plastid‐localised terpene cyclases, membrane‐bound cytochrome P450 monoxygenases and soluble 2‐oxoglutarate‐dependent dioxygenases.

  • Several mechanisms for deactivating gibberellins have been identified, the most prevalent being 2β‐hydroxylation by two families of 2‐oxoglutarate‐dependent dioxygenases.

  • The concentration of the biologically active gibberellins is tightly regulated in most plant tissues at the level of biosynthesis and deactivation.

  • Gibberellin biosynthesis is regulated through feedback and feed‐forward mechanisms as well as by auxin and a range of environmental stimuli.

Keywords: 2‐oxoglutarate‐dependent dioxygenases; plant hormones; biosynthesis; cytochrome P450 monooxygenases; gibberellins; terpene cyclases

Figure 1.

Gibberellin structures, including the simplest C20‐GA, GA12, with the carbon numbering system, and C19‐GA, GA9. Also shown are the principal biologically active compounds, GA1, GA3, GA4 and GA7.

Figure 2.

Gibberellin‐biosynthetic pathway from trans‐geranylgeranyl diphosphate to the biologically active end‐products, GA1, GA3 and GA4, showing the enzymes responsible for each of the steps and the target sites for the main classes of biosynthesis inhibitor that are employed as growth retardants. These inhibitors are exemplified by chlormequat chloride (CCC), an onium‐type inhibitor, paclobutrazol, an N‐containing heterocyclic inhibitor, and the acylcyclohexanedione, prohexadione‐Ca. ent‐copalyl diphosphate, CPP; ent‐copalyl diphosphate synthase, CPS; ent‐kaurene synthase, KS; ent‐kaurenoic acid oxidase, KAO; gibberellin 13‐oxidase, GA13ox; gibberellin 20‐oxidase, GA20ox; gibberellin 3‐oxidase, GA3ox.

Figure 3.

Reactions that result in deactivation of biologically active GAs or conversion of precursors to forms that cannot be activated. The mechanisms illustrated are 2β‐hydroxylation and further oxidation to the GA‐catabolites (red arrows), epoxidation of the 16, 17 double bond (green arrows) and formation of methyl esters (blue arrows). Adapted from Hedden and Thomas .

Figure 4.

Main sites of regulation of GA biosynthesis and deactivation by intrinsic and environmental factors.

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Further Reading

Lange MJP and Lange T (2006) Gibberellin biosynthesis and the regulation of plant development. Plant Biology 8(3): 281–290.

Thomas SG and Hedden P (eds) (2006) Gibberellin metabolism and signal transduction. Plant Hormone Signaling, pp. 147–184. Oxford: Blackwell Publishing.

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Yamaguchi S (2008) Gibberellin metabolism and its regulation. Annual Review of Plant Biology 59: 225–251.

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Hedden, Peter(Aug 2012) Gibberellin Biosynthesis. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023720]