title: Genetic evidence for the reduction of brassinosteroid levels by a BAHD acyltransferase-like protein in Arabidopsis.
abstract: Brassinosteroids (BRs) are a group of steroidal hormones involved in plant development. Although the BR biosynthesis pathways are well characterized, the BR inactivation process, which contributes to BR homeostasis, is less understood. Here, we show that a member of the BAHD (for benzylalcohol O-acetyltransferase, anthocyanin O-hydroxycinnamoyltransferase, anthranilate N-hydroxycinnamoyl/benzoyltransferase, and deacetylvindoline 4-O-acetyltransferase) acyltransferase family may play a role in BR homeostasis in Arabidopsis (Arabidopsis thaliana). We isolated two gain-of-function mutants, brassinosteroid inactivator1-1Dominant (bia1-1D) and bia1-2D, in which a novel BAHD acyltransferase-like protein was transcriptionally activated. Both mutants exhibited dwarfism, reduced male fertility, and deetiolation in darkness, which are typical phenotypes of plants defective in BR biosynthesis. Exogenous BR treatment rescued the phenotypes of the bia1-1D mutant. Endogenous levels of BRs were reduced in the bia1-1D mutant, demonstrating that BIA1 regulates endogenous BR levels. When grown in darkness, the bia1 loss-of-function mutant showed a longer hypocotyl phenotype and was more responsive to exogenous BR treatment than the wild-type plant. BIA1 expression was predominantly observed in the root, where low levels of BRs were detected. These results indicate that the BAHD acyltransferase family member encoded by BIA1 plays a role in controlling BR levels, particularly in the root and hypocotyl in darkness. Taken together, our study provides new insights into a mechanism that maintains BR homeostasis in Arabidopsis, likely via acyl conjugation of BRs.
authors.affiliation: School of Biological Sciences, Seoul National University, Seoul 151-747, Korea.
authors.forename: Hyungmin
authors.initials: H
authors.lastname: Roh
authors.forename: Cheol Woong
authors.initials: CW
authors.lastname: Jeong
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Youn Kyung
authors.initials: YK
authors.lastname: Kim
authors.forename: Sookjin
authors.initials: S
authors.lastname: Lee
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Ahn
authors.forename: Yang Do
authors.initials: YD
authors.lastname: Choi
authors.forename: Jong Seob
authors.initials: JS
authors.lastname: Lee
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060406:Brassinosteroids / Q000096:biosynthesis* / Q000494:pharmacology; D003624:Darkness; D005298:Fertility; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006706:Homeostasis; D018546:Hypocotyl / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D008969:Molecular Sequence Data; D010641:Phenotype; D010802:Phylogeny; D018517:Plant Roots / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D011523:Protoplasts / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D000217:Acyltransferases