Isolation and characterization of a cDNA encoding polyketide reductase in Lotus japonicus

Abstract

Leguminous plants have a unique pathway for production of 5-deoxy-type flavonoids and isoflavonoids that is distinct from the general flavonoid pathways. 5-Deoxy(iso)flavonoids are believed to play important eco-physiological roles as antimicrobial compounds and symbiotic signals toward rhizobia. The branching point of the 5-deoxyflavonoid pathway is the formation of the deoxy-type chalcone (isoliquiritigenin), which is catalyzed by the co-action of chalcone synthase and polyketide reductase (PKR). In the course of the comparative genomics of legume-specific genes, we cloned a putative cDNA for PKR (cPKR1) of a model legume Lotus japonicus (Regel) K. Larsen. Genomic Southern analysis showed that L. japonicus has a gene family composed of two to four paralogous PKR genes. The overexpression of cPKR1 in a red-flowered cultivar of petunia, “Polo Red Target”, reduced anthocyanin accumulation and caused the formation of isoliquiritigenin and its putative derivatives. These results suggested that PKR1 encodes a PKR that functions in planta.