Dwarfism and cytochrome P450-mediated C-6 oxidation of plant steroid hormones

Abstract

BRs (brassinosteroids) are plant steroid hormones that are essential for normal plant development. The dramatic dwarfism exhibited by mutants in the CYP (cytochrome P450) enzymes involved in BR biosynthesis indicates a role for these hormones in plant growth and development. Since the mid-1990s, collaborative research has been geared towards developing a better understanding of the CYP85 class of CYPs involved in BR biosynthesis in both Arabidopsis and tomato. Some of the most recent observations include the fact that certain CYP85 CYPs catalyse the synthesis of the most bioactive BR, BL (brassinolide). Current evidence suggests that evolution of this function may have occurred independently in different dicotyledonous species. Interestingly, BL accumulates in tomato fruits, highlighting a key role for this hormone in fruit development. At the same time as developing a better understanding of the enzymatic function of these CYPs, we have also carried out experiments towards characterizing where and when these genes are expressed and mechanisms of their regulation. As expected for a hormone involved in growth and development, biosynthetic gene promoter activity is associated with young rapidly growing cells and with fruit development.

Drought-tolerant and drought-sensitive genotypes of maize (Zea mays L.) differ in contents of endogenous brassinosteroids and their drought-induced changes

“…BL plays an important role in the development of reproductive organs in these species, whereas CS probably serves as a regulator of plant vegetative growth [ 51 ]. Although BL has already been reported in rice shoots [ 52 ], other authors showed that the step of BR biosynthesis involving the conversion of CS to BL does not seem to exist in rice [ 53 , 54 ]. The same situation seems to apply for other monocot grasses [ 55 , 56 ].…”

Gene expression in diapause-destined embryos of the crustacean, Artemia franciscana

“…Equally vague is whether hormone synthesis occurs in mature females versus embryos, if hormones are activated or inhibited by steroid dehydrogenase, and the cell processes influenced by hormones. Oxidized and reduced nicotinamide are likely to fluctuate in amount as metabolism changes during diapause, supplying triggers for modification of steroid dehydrogenase and cytochrome P450, an NADPH-requiring enzyme capable of irreversible steroid modification (Agarwal and Auchus, 2005;Lieberman et al, 2005;Bishop et al, 2006) and for which mRNA increases during Artemia diapause.…”

From Squalene to Brassinolide: The Steroid Metabolic and Signaling Pathways across the Plant Kingdom

“…Some differences notably exist among angiosperms for the end-products of BR biosynthesis. In Arabidopsis and tomato (Lycopersicon esculentum), these end-products are castasterone (CS) and BL, with BL being the more active of the two (Bishop et al, 2006). In contrast, it seems that rice plants do not produce BL, but use CS as bioactive BR instead (Yamamuro et al, 2000;Hong et al, 2005;Nakamura et al, 2006).…”