title: MAX1 encodes a cytochrome P450 family member that acts downstream of MAX3/4 to produce a carotenoid-derived branch-inhibiting hormone.
abstract: The plant shoot body plan is highly variable, depending on the degree of branching. Characterization of the max1-max4 mutants of Arabidopsis demonstrates that branching is regulated by at least one carotenoid-derived hormone. Here we show that all four MAX genes act in a single pathway, with MAX1, MAX3, and MAX4 acting in hormone synthesis, and MAX2 acting in perception. We propose that MAX1 acts on a mobile substrate, downstream of MAX3 and MAX4, which have immobile substrates. These roles for MAX3, MAX4, and MAX2 are consistent with their known molecular identities. We identify MAX1 as a member of the cytochrome P450 family with high similarity to mammalian Thromboxane A2 synthase. This, with its expression pattern, supports its suggested role in the MAX pathway. Moreover, the proposed enzymatic series for MAX hormone synthesis resembles that of two already characterized signal biosynthetic pathways: prostaglandins in animals and oxilipins in plants.
authors.affiliation: Department of Biology, Area 11, University of York, York, YO10 5YW, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Booker
authors.forename: Tobias
authors.initials: T
authors.lastname: Sieberer
authors.forename: Wendy
authors.initials: W
authors.lastname: Wright
authors.forename: Lisa
authors.initials: L
authors.lastname: Williamson
authors.forename: Barbara
authors.initials: B
authors.lastname: Willett
authors.forename: Petra
authors.initials: P
authors.lastname: Stirnberg
authors.forename: Colin
authors.initials: C
authors.lastname: Turnbull
authors.forename: Murali
authors.initials: M
authors.lastname: Srinivasan
authors.forename: Peter
authors.initials: P
authors.lastname: Goddard
authors.forename: Ottoline
authors.initials: O
authors.lastname: Leyser
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D006728:Hormones / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D018520:Plant Shoots / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D013930:Thromboxane-A Synthase / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D006728:Hormones; C470445:MAX1 protein, Arabidopsis; D002338:Carotenoids; D003577:Cytochrome P-450 Enzyme System; C475746:MAX4 protein, Arabidopsis; D010105:Oxygenases; D013930:Thromboxane-A Synthase