CYP724B2 and CYP90B3 function in the early C-22 hydroxylation steps of brassinosteroid biosynthetic pathway in tomato

Biosci Biotechnol Biochem. 2006 Sep;70(9):2071-80. doi: 10.1271/bbb.60034. Epub 2006 Sep 7.

Abstract

We characterized a new cytochrome P450 monooxygenase (P450), CYP724B2, from tomato (Lycopersicon esculentum). CYP724B2 showed 42% and 62% amino acid sequence identity with Arabidopsis DWARF4/CYP90B1 and rice DWARF11/CYP724B1 respectively. Functional assay of CYP724B2 heterologously expressed in insect cells revealed that CYP724B2 catalyzes C-22 hydroxylation of campesterol, indicating that CYP724B2 is a C-22 hydroxylase. We also isolated a tomato CYP90B homolog (CYP90B3) and found that CYP90B3 is a C-22 hydroxylase as well. CYP724B2 and CYP90B3 showed substrate specificities similar to each other toward the biosynthetic intermediate compounds from campesterol to campestanol. Campesterol was the best substrate, and (24R)-ergost-4-en-3-one was also metabolized to the C-22 hydroxylated product to some extent. On the other hand, the P450s catalyzed C-22 hydroxylation of (24R)-5alpha-ergostan-3-one and campestanol at a trace level, indicating that the compounds after C-5alpha reduction are poor substrates of CYP724B2 and CYP90B3. In addition, cholesterol (C27 sterol) and sitosterol (C29 sterol) were also converted to C-22 hydroxylated products by the P450s. Furthermore, CYP724B2 and CYP90B3 genes were ubiquitously expressed, and their transcript levels were down-regulated by the exogenous application of brassinolide. These findings strongly suggest that CYP724B2 and CYP90B3 function in the early C-22 hydroxylation steps of brassinosteroid biosynthetic pathway in tomato.

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • Expressed Sequence Tags / metabolism
  • Gas Chromatography-Mass Spectrometry
  • Hydroxylation
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Lycopersicon esculentum / enzymology
  • Lycopersicon esculentum / genetics
  • Lycopersicon esculentum / metabolism*
  • Molecular Sequence Data
  • Phylogeny
  • Phytosterols / biosynthesis*
  • Phytosterols / metabolism
  • RNA, Plant / chemistry
  • RNA, Plant / genetics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Spectrophotometry, Ultraviolet

Substances

  • Isoenzymes
  • Phytosterols
  • RNA, Plant
  • Recombinant Proteins
  • Cytochrome P-450 Enzyme System