1. Introduction
Isoflavonoids belong to an important group of secondary
metabolites derived from the phenylpropanoid pathway and are
synthesized predominantly in legumes. Phenylalanine ammonia
lyase (PAL) is the first key enzyme catalyzing the deamination of
L-phenylalanine into cinnamate. Cinnamate 4-hydroxylase (C4H)
and 4-coumarate CoA-ligase (4CL) convert cinnamate into pcoumarate
and finally into p-coumaroyl-CoA in the phenylpropanoid
pathway. Then CHS catalyzes the first committed step
towards flavonoid biosynthesis to form a chalcone scaffold. Chalcone
reductase (CHR) acts as an intermediate of the CHS reaction,
yielding deoxychalcone. CHI catalyzes cyclization of chalcones or
deoxychalcone to form the flavonoid core, flavanone. In legumes,
a branch-point enzyme, IFS, introduces the isoflavonoid biosynthetic