Gibberella fujikuroi pathway

Microbiological Methods. The low substrate specificity of many of the enzymes involved in GA biosynthesis in Gibberella fujikuroi has been utilized for the preparation of higher plant GAs. Suitable analogs of the natural GA-precursors are converted by the fungus to the corresponding GA analogs. It is usual to prevent the synthesis of the natural GAs in order to facilitate purification of the unnatural products. A mutant strain, Bl- la, in which GA biosynthesis is blocked early in the pathway (67) (between ent-kaurenal and ent-kaurenoic acid) has been used. 

Figure 2. The GA biosynthetic pathway from, MVA to GAlsraldehyde. This pathway is found in the fungus Gibberella fujikuroi and higher plants...

U. Bearder, J.R., MacMillan, J., Phinney, B.O. "Fungal products. Part XIV. Metabolic pathways from ent-kaurenoic acid to the fungal gibberellins in mutant Bl-J+la of Gibberella fujikuroi." J. . . Perkin Trans. 1975, 1, 721-726. 

Figure 7 Comparison of the GA biosynthesis pathways in Gibberella fujikuroi and plants.

The kaurenolides and fujenal that are formed by Gibberella fujikuroi are side products from the major biosynthetic pathway. Ent-kaurenoic acid is dehydrogenated to form ent-kaur-6,16-dienoic acid. Epoxidation on the p-face and hydrolysis afforded 7-hydroxykaurenolide (5.117), which was then hydroxylated at C-3 or C-18 to form the dihydroxykaurenolides. The unusual aldehyde anhydride fujenal (5.119) was formed via the 6p,7p-diol. Amongst the metabolites of Gibberella fujikuroi there are several compounds in which the 16-ene is hydrated to give a 16p-tertiary alcohol. These compounds are not metabolized further and represent a dumping mechanism . 

Tudzynski, B., P. Hedden, E. Carrera, and P. Gaskin (2001). The P450-4 gene of Gibberella fujikuroi encodes ent-kaurene oxidase in the gib-berellin biosynthesis pathway App. Environ. Microbiol. 67, 3514-3522. 

In the case of the gibberellins it has been demonstrated that their pathway is identical, or quite similar, in higher plants and in the fungus Gibberella fujikuroi irrespective of whether they function as hormones or as typical secondary products as in the case of the fungus (Eef. 20, 22). 

A simple method of screening for presumptive mutants of Gibberella fujikuroi is described. The use of one mutant (Bl-41a) in the elucidation of the gibberellin biosynthetic pathway from ent-kaurenoic acid and in the metabolism of substrate analogues is briefly reviewed. Some preliminary results are described on the investigation of the inhibition of individual biosynthetic steps by nitrogen in the medium. 

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