Brassinosteroids biosynthetic pathway

Figure 8.3 Brassinosteroid biosynthetic pathway. DWF4 and CPD catalyze the 22a- and 23a-hydroxylation reaction, respectively, in both the early and late C-6 oxidation pathways. CYP85 catalyzes the C-6 oxidation of 6-deoxytyphasterol and 6-deoxocastasterone and tentatively the C-6 oxidation of 6-deoxocathasterone and 6-deoxoteasterone (arrows not shown). DDWF1 dark-induced DIP/7-like protein 1 DWF4 DWARF4 CPD CONSTITUTIVE PHOTOMORPHOGENESIS AND DWARF.

CHOE, S, FUJIOKA, S., NOGUCHI, T., TAKATSUTO, S. YOSHIDA, S., FELDMANN, K.A., Overexpression of DWARF4 in the brassinosteroid biosynthetic pathway results in increased vegetative growth and seed yield in Arabidopsis, Plant J., 2001,26, 1-11. 

Asami, T., Mizutani, M., Fujioka, S., Goda, Fi., Min, Y.K., Shimada, Y., Nakano, T., Takatsuto, S., Matsuyama, T., Nagata, N., Sakata, K. and Yoshida, S. (2001) Selective interaction of triazole derivatives with DWF4, a cytochrome P450 monooxygenase of the brassinosteroid biosynthetic pathway, correlates with brassinosteroid deficiency in planta. /. Biol. Chem., T7B, 25687-91. 

Fujioka, S., Takatsuto, S. and Yoshida, S. (2002) An early C-22 oxidation branch in the brassinosteroid biosynthetic pathway. Plant Physiol., 130, 930-9. 

K, Yoshida S. Selective interaction of triazole derivatives with DWE4, a c)4ochrome P450 monooxygenase of the brassinosteroid biosynthetic pathway, correlates with brassinosteroid deficiency in Planta. J. Biol. Chem. 2001 276 25687-25691. 

An enormous progress in investigating the brassinosteroid biosynthesis was made by mutant analysis and the use of very sensitive analytical methods, leading within few years to a logical and very attractive putative biosynthetic pathway. 

Figure 33 Biosynthetic pathways of brassinosteroids. The larger the arrows, the more principal the routes. Arabidopsis enzymes involved in the biosynthetic reactions are indicated in bold letters.

Like all steroids, brassinosteroids derive from a single common precursor mevalonic acid. Some phytohormones are synthesized totally or in part via the isoprenoid pathway, such as absdsic acid, gibberellins and cytokinins. The importance of this biosynthetic pathway in processes involved with cell cycle regulation and tumorigenesis in mammals is well documented. Having in mind the similarities between certain regulatory systems in plants and animals the question arose whether brassinosteroids as putative plant steroid hormones would show a specific effect on plant tumor cells. 

The biosynthetic pathway for brassinosteroids has not yet been fully elucidated. Models as presented in figure 12.3 for two parallel pathways assigned as the early C-6 oxidation and the late C-6-oxidation pathways have been... 

Brassinosteroids (BRs) are highly oxidized steroidal plant hormones and essential for normal plant growth. BR deficient mutants display strong dwarfism with curly, dark-green leaves in the light, and a deetiolated phenotype with short hypocotyl and open cotyledons in the dark. The characterization of BR-deficient mutants by biochemical studies and molecular genetic analysis has established the biosynthetic pathway for brassinoHde (BL), the biochemically most active BR. 

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