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

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Abstract
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.