title: Bikinin-like inhibitors targeting GSK3/Shaggy-like kinases: characterisation of novel compounds and elucidation of their catabolism in planta.
abstract: BACKGROUND
  Plant GSK-3/Shaggy-like kinases are key players in brassinosteroid (BR) signalling which impact on plant development and participate in response to wounding, pathogens and salt stress. Bikinin was previously identified in a chemical genetics screen as an inhibitor targeting these kinases. To dissect the structural elements crucial for inhibition of GSK-3/Shaggy-like kinases by bikinin and to isolate more potent compounds we synthesised a number of related substances and tested their inhibitory activity in vitro and in vivo using Arabidopsis thaliana.
  
  
  RESULTS
  A pyridine ring with an amido succinic acid residue in position 2 and a halogen in position 5 were crucial for inhibitory activity. The compound with an iodine substituent in position 5, denoted iodobikinin, was most active in inhibiting BIN2 activity in vitro and efficiently induced brassinosteroid-like responses in vivo. Its methyl ester, methyliodobikinin, showed improved cell permeability, making it highly potent in vivo although it had lower activity in vitro. HPLC analysis revealed that the methyl residue was rapidly cleaved off in planta liberating active iodobikinin. In addition, we provide evidence that iodobikinin and bikinin are inactivated in planta by conjugation with glutamic acid or malic acid and that the latter process is catalysed by the malate transferase SNG1.
  
  
  CONCLUSIONS
  Brassinosteroids participate in regulation of many aspects of plant development and in responses to environmental cues. Thus compounds modulating their action are valuable tools to study such processes and may be an interesting opportunity to modify plant growth and performance in horticulture and agronomy. Here we report the development of bikinin derivatives with increased potency that can activate BR signalling and mimic BR action. Methyliodobikinin was 3.4 times more active in vivo than bikinin. The main reason for the superior activity of methyliodobikinin, the most potent compound, is its enhanced plant tissue permeability. Inactivation of bikinin and its derivatives in planta involves SNG1, which constitutes a novel pathway for modification of xenobiotic compounds.
authors.affiliation: GMI-Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna Biocenter, Dr, Bohr-Gasse 3, Vienna 1030, Austria. wilfried.rozhon@wzw.tum.de.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Rozhon
authors.forename: Wuyan
authors.initials: W
authors.lastname: Wang
authors.forename: Franz
authors.initials: F
authors.lastname: Berthiller
authors.forename: Juliane
authors.initials: J
authors.lastname: Mayerhofer
authors.forename: Tingting
authors.initials: T
authors.lastname: Chen
authors.forename: Elena
authors.initials: E
authors.lastname: Petutschnig
authors.forename: Tobias
authors.initials: T
authors.lastname: Sieberer
authors.forename: Brigitte
authors.initials: B
authors.lastname: Poppenberger
authors.forename: Claudia
authors.initials: C
authors.lastname: Jonak
mesh_terms: D000631:Aminopyridines / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D055162:Biocatalysis / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006868:Hydrolysis / Q000187:drug effects; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development; D008293:Malates / Q000378:metabolism; D013058:Mass Spectrometry; D008745:Methylation / Q000187:drug effects; D010539:Permeability / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D012015:Reference Standards; D015398:Signal Transduction / Q000187:drug effects; D013056:Spectrophotometry, Ultraviolet; D013386:Succinates / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*
chemical_list: D000631:Aminopyridines; D029681:Arabidopsis Proteins; D008293:Malates; D047428:Protein Kinase Inhibitors; D013386:Succinates; C543414:bikinin; C030298:malic acid; D038362:Glycogen Synthase Kinase 3