Kaurene, biosynthesis

Aach, H., Bose, G. and Graebe, J.E. (1995) Ent-kaurene biosynthesis in a cell-free system from wheat (Triticum aestivum) seedlings and the localisation of ent-kaurene s)mthetase in plastids of three species. Planta, 197, 333-42. 

Ceccarelli N, Lorenzi R, Alpi A (1981c) Kaurene biosynthesis in intact Phaseolus coccineus suspensors. Experientia (Basel) 37 478... 

The mode of action of CCC is attributed to the inhibition of / Akaurene synthetase A, the enzyme that drives the biosynthesis of geranyigeranylpyrophosphate by copalyl pyrophosphate to /-kaurene. The compound is registered in Europe to control lodging and is registered with the EPA. 

Since GAs as diterpenes share many intermediates in the biosynthetic steps leading to other terpenoids, eg, cytokinins, ABA, sterols, and carotenoids, inhibitors of the mevalonate (MVA) pathway of terpene synthesis also inhibit GA synthesis (57). Biosynthesis of GAs progresses in three stages, ie, formation of / Akaurene from MVA, oxidation of /-kaurene to GA 2" hyde, and further oxidation of the GA22-aldehyde to form the different GAs more than 70 different GAs have been identified. 

Most of the GA-synthesis inhibitors characterized so far affect two segments of the compHcated pathway from MVA to the many different GAs identified. The cycHzation reactions that produce / Akaurene are inhibited by the onium growth retardants, and the oxidations of /-kaurene to /-kaurenoic acid are sensitive to heterocycHc triazoles such as paclobutrazol and similar compounds. Other enzymes in the pathway are points for pathway dismption by as yet undeveloped GA biosynthesis inhibitors (236). 

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. 

HELLIWELL, C.A., SULLIVAN, JA. MOULD, R.M., GRAY, J.C., PEACOCK W.J., DENNIS, E.S., A plastid envelope location of Arabidopsis enf-kaurene oxidase links the plastid and endoplasmic reticulum steps of the gibberellin biosynthesis pathway., Plant J., 2001,28,201-208... 

The retardation effect of all these substances can be reversed by gibberellins. Furthermore, it has been possible, in the case of some of these substances, to detect precisely the point of attack or site of action in the gibberellin biosynthesis sequence. As can be seen from Figure 3, it is assumed that the onium compounds inhibit the cyclization of geranylgeranyl pyrophosphate to copalyl pyrophosphate (7), whereas it has been demonstrated in cell-free systems that pyrimidines, norbornenodiazetines, and triazoles inhibit the sequential oxidation of ent-kaurene to ent-kaurenoic acid (fj, 9). 

The partial synthesis from epicandicandiol of some C- and H-labelled kaurene derivatives has been described.These have possible application in the study of the biosynthesis of the Isodon diterpenoids. The syntheses of [17- C]kaur-16-en-20-ol from enmein and of 3-oxygenated derivatives of [17- C]kaur-16-ene from ent-3jS,19-dihydroxy-kaur-16-ene have also been described. The synthesis of radioactive aphidicolin has also been reported. It has been shown ° that ent-kaur-15-ene is formed by the dwarf mutant (ds) of maize in place of ent-kaur-16-ene. 

Sun, T.-P. and Kamiya, Y. (1994) The Arabidopsis GAl locus encodes the cyclase ent-kaurene synthetase A of gibberellin biosynthesis. Plant Cell, 6, 1509-18. 

Yamaguchi, S., Sun, T.P., Kawaide, H. and Kamiya, Y. (1998) The ga2 locus of Arabidopsis thaliana encodes ent-kaurene synthase of gibberellin biosynthesis. Plant Physiol, 116,127-78. 

A series of analogues, (4) and (5), of the precursors of squalene, in which the carbinol oxygen is replaced by a methylene group, inhibited the formation of squalene from [2- C]- and [S- HaJ-MVA by rat liver squalene synthetase. These phosphonophosphates also inhibited the biosynthesis of kaurene from MVA in a cell-free system from Ricinus communis, but the corresponding phosphonates were only weakly inhibitory. The formation of labelled squalene from a mixture of [2- C]MVA and [l- H]presqualene alcohol pyrophosphate by the squalene synthetase preparation was completely inhibited by the addition of (5) to the incubation... 

This plant growth regulatory activity is due to inhibition of the biosynthesis of gibberellins (j>), at the three oxidation steps between ent-kaurene and ent-kaurenoic acid (Figure 2). 

Biosynthesis (Chapter 6).— E>etailed studies have been reported with individual enzymes responsible for the early stages of terpenoid biosynthesis. The mechanism whereby two molecules of famesyl pyrophosphate couple to furnish squalene is still uncertain and the structure of the C30 pyrophosphate intermediate isolated by Rilling in 1966 remains elusive. The genesis of the monoterpenoid portion of the indole alkaloids has been intensively studied. Of special interest was the discovery of the bismonoterpenoid foliamenthin, which is a derivative of the indole alkaloid precursor secologanin. The biosynthesis of the gibberellins has received detailed attention on both sides of the Atlantic. nr-kaurene, the parent, is formed via geranylgeranyl pyrophosphate and enr-copalyl pyrophosphate and this seems to follow a... 

In confirmation of earlier indieations that enf-kaurene synthesis is localised in plastids [60-62], Aaeh et al. [44] demonstrated clearly the presence of CPS/EKS activity in the stroma of wheat and pea etioplasts and leucoplasts from C. maxima endosperm. They showed, furthermore, that mature chloroplasts contain no CPS/EKS activity and that the activity is associated with dividing cells in the meristem [45]. These findings, together with the demonstration that CPS is targeted to plastids, provide firm evidence that the first part of GA biosynthesis takes place in plastids. 

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. 

Another new technique for the study of biosynthesis is the use of g.c.-m.s. MacMillan and co-workers have shownin this way that kaurene and related products had incorporated four " C atoms per molecule and that the specific activity was equal at all four positions. Full details have appeared of the study concerning the ring-contraction in the formation of the gibbane skeleton. The key step seems to involve a hydride shift [see (66) -+ (67)]. A late stage in gib-berellic acid (A -68) biosynthesis might involve GAj (68). However, this compound was incorporated only into GAg (69) and its glucoside. ... 

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