Identification of cDNAs encoding pterocarpan reductase involved in isoflavan phytoalexin biosynthesis in Lotus japonicus by EST mining

Isoflavans and pterocarpans are the major biosynthetically connected phytoalexins in legumes. A search of the expressed sequence tag library of a model legume Lotus japonicus, which produces an (−)-isoflavan, for homologs of phenylcoumaran benzylic ether reductase catalyzing the reductive cleavage of dihydrofurans, yielded seven full-length cDNAs, and the encoded proteins were analyzed in vitro. Four of them cleaved the dihydrofuran of a pterocarpan medicarpin to yield an isoflavan (−)-vestitol and were designated pterocarpan reductase (PTR). Two PTRs displayed enantiospecificity to (−)-medicarpin, representing genuine L. japonicus PTRs, while the other two lacked enantiospecificity and were presumed to be evolutionarily primitive types.