If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: GA3 biosynthesis
|Superclasses:||Biosynthesis → Hormones Biosynthesis → Plant Hormones Biosynthesis → Gibberellins and Gibberellin Precursors Biosynthesis → Gibberellins biosynthesis|
|Biosynthesis → Secondary Metabolites Biosynthesis → Terpenoids Biosynthesis → Diterpenoids Biosynthesis → Gibberellins and Gibberellin Precursors Biosynthesis → Gibberellins biosynthesis|
Some taxa known to possess this pathway include : Fusarium fujikuroi
Expected Taxonomic Range: Fungi
Gibberellins are diterpenes which, in higher plants, are synthesized in the plastids from glyceraldehyde-3-phosphate and pyruvate via the isopentenyl diphosphate (IPP). They all have either 19 or 20 carbon units grouped into either four or five ring systems (see C20-gibberellin skeleton and C19-gibberellin skeleton, respectively). The fifth ring is a lactone ring. GAs containing a tetracyclic ent-gibberellane structure (C20-gibberellin skeleton) are called C20-GAs, whereas GAs containing a pentacyclic 20-nor-ent-gibberellane structure (C19-gibberellin skeleton) are called C19-GAs. C20-GAs do not usually have biological activity but can be metabolized to active C19-GAs (note that not all C19-GAs are bioactive).
At the time of this review, 136 fully characterized gibberellins (starting with GA1 [MacMillan68]) have been identified in more than a hundred vascular plant species, seven bacteria and seven fungi [Sponsel04, MacMillan01]. Of these gibberellins only a few have biological activity. Many of the GAs identified early in the history of the discovery of these hormones are the ones which possess the highest biological activity. These include GA1, GA3, GA4, GA5, GA6 and GA7. GA1 is the most active GA for stem elongation in Zea mays and Pisum sativum, while GA4 is the most active GA in Cucurbitaceae and in Arabidopsis thaliana. GA3 (gibberellic acid), on the other hand, has been identified in more than 40 plants and is the major GA in the fungus Fusarium fujikuroi. GA3 is used commercially to promote seed germination, stem elongation and fruit growth. In Lolium, GA5 and GA6 have been shown to enhance flowering, whilst GA1 and GA4 enhanced stem elongation [King03].
Gibberellins are believed to be synthesized in young tissues of the shoot and also the developing seed. It is uncertain whether young root tissues also produce gibberellins. There is also some evidence that leaves may be the source of some biosynthesis.
Certain commercial chemicals which are used to stunt growth do so in part because they block the synthesis of gibberellins. Some of these chemicals are phosphon D, AMO-1618, cycocel, ancymidol and paclobutrazol (more inhibitors of GA biosynthesis can be found in [Sponsel04]). Active gibberellin A3 is degraded much slower which helps to explain the symptoms observed in the disease bakanae caused by the rice pathogen Fusarium fujikuroi. This pathogen is used in industry for its ability to produce large amounts of GA3 which it secretes. Incidentally, GA3 is only a minor GA in most plant species.
About This Pathway
The biosynthesis of GA3 in Fusarium fujikuroi occurs through successive oxidation steps via GA14. Unlike what is seen in plants (see gibberellin biosynthesis II (early C-3 hydroxylation)), the main route of production of GA14 occurs via GA14-aldehyde rather than GA12, which only represents a minor route of GA14 synthesis in Fusarium [Rojas01]. Following the production of GA14 the gibberellin 20-oxidase encoded by gene P450-2, catalyzes the removal of C-20, thereby forming the C19-skeleton in GA4. This protein (GfGA20OX) differs from its plant counterpart in that it is a P450 monooxygenase rather than a dioxygenase. Distinctly from the plant GA 20-oxidases, GfGA20OX does not appear to accumulate the alcohol and aldehyde intermediates observed with dioxygenases, indicating that in the case of the Fusarium enzyme, the intermediates may not be released from the enzyme active site and are instead efficiently sequentially metabolized to form GA4 [Tudzynski02]. The following two steps are catalyzed by a gibberellin 1,2-desaturase and a gibberellin 13-hydroxylase to produce GA7 and finally GA3, respectively. The main (but not only) electron donor for the monooxygenases of this pathway in Gibberellla is the NADPH-cytochrome P450 reductase CPR-Gf [Malonek04].
Variants: gibberellin biosynthesis I (non C-3, non C-13 hydroxylation) , gibberellin biosynthesis II (early C-3 hydroxylation) , gibberellin biosynthesis III (early C-13 hydroxylation) , gibberellin biosynthesis V
Malonek04: Malonek S, Rojas MC, Hedden P, Gaskin P, Hopkins P, Tudzynski B (2004). "The NADPH-cytochrome P450 reductase gene from Gibberella fujikuroi is essential for gibberellin biosynthesis." J Biol Chem 279(24);25075-84. PMID: 15037621
Rojas01: Rojas MC, Hedden P, Gaskin P, Tudzynski B (2001). "The P450-1 gene of Gibberella fujikuroi encodes a multifunctional enzyme in gibberellin biosynthesis." Proc Natl Acad Sci U S A 98(10);5838-43. PMID: 11320210
Cho04a: Cho EM, Okada A, Kenmoku H, Otomo K, Toyomasu T, Mitsuhashi W, Sassa T, Yajima A, Yabuta G, Mori K, Oikawa H, Toshima H, Shibuya N, Nojiri H, Omori T, Nishiyama M, Yamane H (2004). "Molecular cloning and characterization of a cDNA encoding ent-cassa-12,15-diene synthase, a putative diterpenoid phytoalexin biosynthetic enzyme, from suspension-cultured rice cells treated with a chitin elicitor." Plant J 37(1);1-8. PMID: 14675427
Helliwell01: Helliwell CA, Chandler PM, Poole A, Dennis ES, Peacock WJ (2001). "The CYP88A cytochrome P450, ent-kaurenoic acid oxidase, catalyzes three steps of the gibberellin biosynthesis pathway." Proc Natl Acad Sci U S A 98(4);2065-70. PMID: 11172076
Itoh01: Itoh H, Ueguchi-Tanaka M, Sentoku N, Kitano H, Matsuoka M, Kobayashi M (2001). "Cloning and functional analysis of two gibberellin 3 beta -hydroxylase genes that are differently expressed during the growth of rice." Proc Natl Acad Sci U S A 98(15);8909-14. PMID: 11438692
Morrone10: Morrone D, Chen X, Coates RM, Peters RJ (2010). "Characterization of the kaurene oxidase CYP701A3, a multifunctional cytochrome P450 from gibberellin biosynthesis." Biochem J 431(3);337-44. PMID: 20698828
Nemoto04: Nemoto T, Cho EM, Okada A, Okada K, Otomo K, Kanno Y, Toyomasu T, Mitsuhashi W, Sassa T, Minami E, Shibuya N, Nishiyama M, Nojiri H, Yamane H (2004). "Stemar-13-ene synthase, a diterpene cyclase involved in the biosynthesis of the phytoalexin oryzalexin S in rice." FEBS Lett 571(1-3);182-6. PMID: 15280039
Otomo04: Otomo K, Kenmoku H, Oikawa H, Konig WA, Toshima H, Mitsuhashi W, Yamane H, Sassa T, Toyomasu T (2004). "Biological functions of ent- and syn-copalyl diphosphate synthases in rice: key enzymes for the branch point of gibberellin and phytoalexin biosynthesis." Plant J 39(6);886-93. PMID: 15341631
Rojas04: Rojas MC, Urrutia O, Cruz C, Gaskin P, Tudzynski B, Hedden P (2004). "Kaurenolides and fujenoic acids are side products of the gibberellin P450-1 monooxygenase in Gibberella fujikuroi." Phytochemistry 65(7);821-30. PMID: 15081281
Tudzynski01: Tudzynski B, Hedden P, Carrera E, Gaskin P (2001). "The P450-4 gene of Gibberella fujikuroi encodes ent-kaurene oxidase in the gibberellin biosynthesis pathway." Appl Environ Microbiol 67(8);3514-22. PMID: 11472927
Tudzynski03: Tudzynski B, Mihlan M, Rojas MC, Linnemannstons P, Gaskin P, Hedden P (2003). "Characterization of the final two genes of the gibberellin biosynthesis gene cluster of Gibberella fujikuroi: des and P450-3 encode GA4 desaturase and the 13-hydroxylase, respectively." J Biol Chem 278(31);28635-43. PMID: 12750377
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