Inactivation of Brassinosteroid Biological Activity by a Salicylate-inducible Steroid Sulfotransferase from Brassica napus

Abstract

Recent discoveries from brassinosteroid-deficient mutants led to the recognition that plants, like animals, use steroids to regulate their growth and development. We describe the characterization of one member of a Brassica napus sulfotransferase gene family coding for an enzyme that catalyzes the O-sulfonation of brassinosteroids and of mammalian estrogenic steroids. The enzyme is specific for the hydroxyl group at position 22 of brassinosteroids with a preference for 24-epicathasterone, an intermediate in the biosynthesis of 24-epibrassinolide. Enzymatic sulfonation of 24-epibrassinolide abolishes its biological activity in the bean second internode bioassay. This mechanism of hormone inactivation by sulfonation is similar to the modulation of estrogen biological activity observed in mammals. Furthermore, the expression of the B. napus steroid sulfotransferase genes was found to be induced by salicylic acid, a signal molecule in the plant defense response. This pattern of expression suggests that, in addition to an increased synthesis of proteins having antimicrobial properties, plants respond to pathogen infection by modulating steroid-dependent growth and developmental processes.Many developmental and physiological processes in organisms ranging from fungi to humans are regulated by a small number of steroid hormones. However, until recently the plant kingdom was almost completely excluded from the field of steroid endocrinology. The recent demonstration that the Arabidopsis de-etiolated2 (det2) and the constitutive photomorphogenesis and dwarfism (cpd) mutants are defective in the synthesis of brassinosteroids (BRs) 1 focused attention toward the physiological function of steroids in plants (1, 2). Since these initial discoveries, several other mutants impaired in BR synthesis or perception have been characterized at the molecular level (3-5).BRs have been shown to elicit a broad spectrum of responses including the promotion of cell elongation and cell division, inhibition of de-etiolation in the dark, repression of light-regulated genes in the dark, and repression of stressregulated genes (2, 6, 7). Brassinolide was the first BR isolated and characterized from plants (Fig.

Biochemical and Molecular Characterization of a Hydroxyjasmonate Sulfotransferase from Arabidopsis thaliana

“…However, these values are probably not reflecting the real affinity of the enzyme for its substrates, because the assay mixture contained four steroisomers as a result of the presence of two chiral carbons at C-3 and C-7 of the cyclopentanone ring. Substrate-dependent stereoselectivity has been reported for the rat hydroxysteroid and phenol STs and more recently for the B. napus brassinosteroid ST (19,33). Although the stereochemistry of naturally occurring 12-OHJA has not been established unambiguously, naturally occurring 12-OHJA seems to have a cis conformation, and it was shown that cis-12-OHJA has a much stronger tuber-inducing activity than the trans isomer (34).…”

“…Furthermore, the fact that JA is not a competitive inhibitor of the reaction indicates that the presence of a hydroxyl group at positions 11 or 12 on the side chain is required for binding at the active site of the enzyme. The strict structural specificity exhibited by AtST2a is a common feature of plant STs and has been observed with the flavonoid, gallic acid glucoside, and brassinosteroid STs (19,37).…”

“…Sulfonate conjugation not only facilitates transport and excretion of hydrophobic molecules by increasing their water solubility, it abolishes the biological activity of hormones such as estrogens. Recently, the characterization of a brassinosteroid sulfotransferase (ST) from Brassica napus demonstrated that plants like animals use the sulfonation reaction to control the biological activity of hormones (19). The sulfonation reaction can also lead to the production of biologically active molecules.…”

RAV-Like1Maintains Brassinosteroid Homeostasis via the Coordinated Activation ofBRI1and Biosynthetic Genes in Rice

“…Its levels correlate with the expression patterns of the BR biosynthetic genes BR-6-oxidase and DWARF4 and with the BR synthesis-related P450 genes (Bancos et al, 2002;Shimada et al, 2003). The inactivation of BRs by degradation and conjugation mechanisms contributes to the homeostasis of BRs (Neff et al, 1999;Rouleau et al, 1999;Nakamura et al, 2005;Poppenberger et al, 2005).…”

Identification and characterization of a novel abiotic stress responsive sulphotransferase gene (OsSOT9) from rice

“…[18,27] The expression pattern of B. napus increased after treatment with salicylic acid and ethanol, which further showed the potential function of these enzymes in the stress response. [18,28] In this paper, we screened a stress tolerance candidate gene OsSOT9 from cultivar Pei'ai 64S (photothermo-sensitive genic male sterile line), which is the maternal parent of the super hybridization rice LiangYou-Pei-Jiu (LYP9) by GeneChip Rice Genome Array and quantitative real-time polymerase chain reaction (qRT-PCR).…”