Pisatin, biosynthesis

HI4 OMT from G. echinata is thought to be distinct from the M. sativa lOMT, because a separate daidzein 7-OMT is present in G. echinata, prompting the suggestion that the lOMT be renamed D70MT. The HI4 OMT amino acid sequence is closely related to that of the SAM (+)-6a-hydroxymaackiain 3-(9-methyltransferase (HM30MT), which carries out a similar reaction in (+)-pisatin biosynthesis in Pisum sativum (pea) (see Section 3.9.7). The... 

Paiva, N.L. et al., Molecular cloning of isoflavone reductase from pea (Pisum sativum L.) evidence for a 3R-isoflavanone intermediate in (+)-pisatin biosynthesis. Arch. Biochem. Biophys., 312, 501, 1994. 

Hiramatsu M, Ichinose Y, Shiraishi T, Oku H, Ouchi S (1986) Regulation of pisatin biosynthesis in pea leaves by elicitor and suppressor produced by Mycosphaerella pinodes. Ann Phytopathol Soc Jpn 52 53-58... 

Akashi, T., VanEtten, H.D., Sawada, Y. et al. (2006b). Catalytic specificity of pea O-methyltransfer-ases suggests gene duplication for (+)-pisatin biosynthesis. Phytochemistry, 67,2525-2530. 

DiCenzo, G.L. VanEtten, H.D. (2006). Studies on the late steps of (+) pisatin biosynthesis Evidence for (-) enantiomeric intermediates. Phytochemistry, 67, 675-683. 

HI4 OMT protein showed activity against the 3-hydroxyl of a compound related to (+)-6a-hydroxymaackiain, ( + )-medicarpin, suggesting HM OMT may be functionally identical to HM30MT. However, the HM30MT substrate is only found in species making (+)-pisatin. The G. echinata HM OMT cDNA was used to isolate HM OMT cDNAs from L. japonicus, M. truncatula, and other legumes. Both HM OMT and lOMT may be involved in formono-netin biosynthesis, perhaps in the same tissues, and the formation of heterodimers of similar OMTs has been reported. 

The biosynthesis of pterocarpans, which include well-known phytoalexins such as medicarpin in alfalfa (Medicago sativa) [Baker et al., 1989 Higgins, 1972 Oommen et al., 1994 He and Dixon, 2000] (Fig. 21.2), pisatin in pea... 

WU, Q., PREISIG, C.L., VANETTEN, H.D., Isolation of the cDNAs encoding (+)6a-hydroxymaackiain 3-O-methyltransferase, the terminal step for the biosynthesis of the phytoalexin pisatin in Pisum sativum L. Plant Mol. Biol., 1997, 35,551-560. 

The pterocarpan pisatin was first isolated and characterized as a phytoalexin in Pi sum sativum in the early 1960s.234 235 Since then, structurally diverse phytoalexins have been reported from more than 30 families of higher plants. Much progress is also being made in studies on phytoalexin biosynthesis based on genomic information. 

---