Biosynthesis of the biphenyl phytoalexin aucuparin in Sorbus aucuparia cell cultures treated with Venturia inaequalis.
Aucuparin is the most widely distributed biphenyl phytoalexin in the rosaceous subtribe Pyrinae, which includes the economically important fruit trees apple and pear. The biphenyl scaffold is formed by biphenyl synthase, which catalyzes biosynthesis of 3,5-dihydroxybiphenyl. Conversion of this precursor to aucuparin (3,5-dimethoxy-4-hydroxybiphenyl) was studied in cell cultures of Sorbus aucuparia after treatment with an elicitor preparation from the scab-causing fungus Venturia inaequalis. The sequence of the biosynthetic steps detected was O-methylation - 4-hydroxylation - O-methylation. The two alkylation reactions were catalyzed by distinct methyltransferases, which differed in pH and temperature optima as well as stability. Biphenyl 4-hydroxylase was a microsomal cytochrome P450 monooxygenase, whose activity was appreciably decreased by the addition of established P450 inhibitors. When fed to V. inaequalis-treated S. aucuparia cell cultures, radioactively labeled 3,5-dihydroxybiphenyl was not only incorporated into aucuparin but also into the dibenzofuran eriobofuran, the accumulation of which paralleled that of aucuparin. However, biphenyl 2'-hydroxylase activity proposed to be involved in dibenzofuran formation was detected in neither microsomes nor cell-free extracts in the presence of NADPH and 2-oxoglutarate, respectively. Nevertheless, a basis for studying biphenyl biosynthesis at the gene level is provided.
Institute of Pharmaceutical Biology, Technische Universität Braunschweig, Mendelssohnstr. 1, 38106 Braunschweig, Germany.
Mohammed N A
MN
Khalil
Till
T
Beuerle
Andreas
A
Müller
Ludger
L
Ernst
Vijaya B R
VB
Bhavanam
Benye
B
Liu
Ludger
L
Beerhues
D001203:Ascomycota / Q000378:metabolism*; D001572:Benzofurans / Q000378:metabolism; D001713:Biphenyl Compounds / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000737:chemistry; D027845:Malus / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism*; D031989:Pyrus / Q000378:metabolism; D012717:Sesquiterpenes / Q000737:chemistry / Q000378:metabolism*; D031994:Sorbus / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D000094162:Phytoalexins
D001572:Benzofurans; D001713:Biphenyl Compounds; D003577:Cytochrome P-450 Enzyme System; D007656:Ketoglutaric Acids; D009097:Multienzyme Complexes; D012717:Sesquiterpenes; D000094162:Phytoalexins; C482658:biphenyl synthase, Sorbus aucuparia; C000588997:aucuparin; C010574:biphenyl; C023614:dibenzofuran; C019046:4-phenylphenol
Biosynthesis; Biphenyls; Dibenzofurans; Phytoalexins; Sorbus aucuparia; Venturia inaequalis