CDNA cloning and characterization of chalcone isomerase-fold proteins from snapdragon (Antirrhinum majus L.) flowers

CDNAs coding for the chalcone isomerase-fold proteins (CIFP) of the snapdragon (Antirrhinum majus L.) were cloned and characterized. One of these CIFPs was a Cluster-1 member of the CIFP family, which was a catalytically active chalcone isomerase and thus termed AmCHI1. The recombinant AmCHI1 could act on 2′,4,4′,6′-tetrahydroxychalcone (THC) and 2′,3,4,4′,6′-pentahydroxychalcone (PHC) to produce naringenin and eriodictyol with k_cat/K_m values of 0.25 s^-1 μM^-1 and 0.071 s^-1 μM^-1, respectively, at pH 7.5 and 4°C. The enzyme could not act on 4′-O-glucosides of THC and PHC. In the yellow snapdragon petals (cv. Yellow Butterfly), the temporal expression patterns of AmCHI1 were consistent with the observed temporal accumulation patterns of flavones. Thus, regulation of the AmCHI1 transcription and substrate specificity of the expressed AmCHI1 should serve as the key mechanisms that allows for partitioning of the flavonoid biosynthetic pathways into the aurones and the non-aurone flavonoids in snapdragon petal cells. The other CIFP cDNA, AmCIFP4, was a Cluster-4 member of the family and was similar in its primary structure to enhancers of the flavonoid production of torenia (Torenia×hybrida) and petunia (Petunia×hybrida). AmCIFP4 was more abundantly expressed than AmCHI1 irrespective of flower color.