Recent advances in brassinosteroid biosynthetic pathway: insight into novel brassinosteroid shortcut pathway

Abstract

Brassinosteroids (BRs) are plant steroid hormones involved in plant growth and environmental adaptation. It is well known that oxidation/hydroxylation steps in the BR biosynthetic pathway are catalyzed by cytochrome P450 enzymes. It has been proposed that brassinolide is biosynthesized from campesterol via campestanol (CN) in the original BR biosynthetic pathway. However, a recent enzymatic analysis of cytochrome P450 enzymes and re-evaluation of the endogenous amount of BRs in BR-deficient mutants included an investigation of the novel BR biosynthetic pathway (CN-independent pathway) not via CN. This review highlights comprehensive recent advances in the biochemical research of BR biosynthetic enzymes and the CN-independent pathway. This review also focuses the biosynthesis inhibitors and the antagonists/agonists that are utilized not only as plant growth regulators but also as tools for the chemical and biological investigation of the physiological functions of BRs.

Comprehensive Overview of the Brassinosteroid Biosynthesis Pathways: Substrates, Products, Inhibitors, and Connections

“…The reaction is catalyzed by the C-4 sterol methyl oxidase 2 (SMO2) ( Figure 1 ; Figure S1 ). Then, episterol is converted to 5-dehydroepisterol by the sterol C-5(6) desaturase encoded by the DWF7 gene (also known as STE1 ), which is then converted to 24-methyleneCR (catalyzed by 7-dehydrocholesterol reductase encoded by the DWF5 gene) ( Choe, 2006 ; Ohnishi, 2018 ). Further stages of the C 28 -BR biosynthesis may proceed through two parallel pathways, called the late and early C-22 oxidation pathway.…”

“…However, an essential difference between the C-22 oxidation sub-pathways is the synthesis of 6-deoxocathasterone (6-deoxoCT) from (22 S ,24 R )-22-hydroxy-5α-ergostan-3-one, without synthesis of campestanol (CN) (CN-independent pathway of BRs biosynthesis) as a result of the early C-22 oxidation. On the other hand, in each stage of the late C-22 oxidation pathway, the compound can be hydroxylated by the C-22α hydroxylase into hydroxygenated forms of early C-22 pathway ( Choe, 2004 ; Ohnishi, 2018 ). Moreover, biochemical changes of 22-hydroxymethyleneCR can lead to the synthesis of 6-deoxodolichosterone, which may be further converted into dolichosterone (DS), and dolicholide (DL), as well as to castasterone (CS) and BL ( Roh et al., 2017 ).…”

Roles of cytochromes P450 in plant reproductive development

“…The synthesis of brassinosteroids (BRs), which are a type of polyhydroxysteroids that are essential for plant growth and development (Planas-Riverola et al, 2019) basically depends on CYPs' activities (Ohnishi, 2018). BRs act regulating the division, elongation and differentiation of numerous cell types throughout different stages of the plant life cycle (Fig.…”

“…DWF4/CYP90B1 catalyzes the C-22 hydroxylation of CR, CPD/CYP90A1 (Ohnishi et al, 2012) is involved in the C-3 dehydrogenation of steroid skeletons and CYP90C1/ROT3 and CYP90D1 have redundant functions as C-23 hydroxylases (Kim et al, 2005a). CYP85A1 and CYP85A2 were found to catalyze the C-6 oxidation reaction (Ohnishi, 2018). The structural diversity of BRs is also generated by the action of several groups of CYPs (Ohnishi, 2018).…”

“…CYP85A1 and CYP85A2 were found to catalyze the C-6 oxidation reaction (Ohnishi, 2018). The structural diversity of BRs is also generated by the action of several groups of CYPs (Ohnishi, 2018).…”