Structures and functions of chalcone polyketide reductase genes in Lotus japonicus

Abstract

The biosynthesis of legume-specific 5-deoxyflavonoids requires the co-action of chalcone polyketide reductase (PKR) and chalcone synthase (CHS) to produce 6'-deoxychalcone. In contrast to extensive studies on CHSs, no detailed information of PKR genes is available. Thus, we studied PKR genes of a model legume Lotus japonicus.
Homology-based PCR yielded two cDNAs, which are ca. 80% identical to known PKRs. Genome analysis showed that four PKR genes (PKR1-4) form a cluster within a 58 kb region. The comparison of exon-intron structures suggests that PKR3 should be a pseudogene. Expression analysis revealed constitutive expression of PKR4 and transient increase of PKR1 and PKR2 mRNAs after elicitation. This result is consistent with the existence of W-box motif involved in plant defense responses in the promoters of PKR1 and PKR2. PKR-transgenic petunia displayed decreased amounts of anthocyanins and the emergence of 6'-deoxychalcone.