Chalcone Isomerase a Key Enzyme for Anthocyanin Biosynthesis in Ophiorrhiza japonica

Abstract

Anthocyanins are distributed ubiquitously to terrestrial plants and chalcone isomerase (CHI) catalyzes the stereospecific isomerization of chalcones - a committed step in the anthocyanin biosynthesis pathway. In this study, one gene encoding CHI was isolated from <i>Ophiorrhiza japonica</i> and designated as <i>OjCHI</i>. Multiple sequence alignments and phylogenetic analysis revealed that OjCHI had the conserved CHI active site residues and was classified into type I CHI group. In order to better understand the mechanisms of anthocyanin synthesis in <i>O. japonica</i>, integrative analysis between metabolites and <i>OjCHI</i> expression was conducted. The results showed <i>OjCHI</i> expression matched the accumulation patterns of anthocyanins not only in different tissues but also during the flower developmental stages, suggesting the potential roles of <i>OjCHI</i> in the biosynthesis of anthocyanin. Then biochemical analysis indicated that recombinant OjCHI protein exhibited a typical type I CHI activity which catalyzed the production of naringenin from naringenin chalcone. Moreover, expressing <i>OjCHI</i> in Arabidopsis <i>tt5</i> mutant restored the anthocyanins and flavonols phenotype of hypocotyl, cotyledon and seed coat, indicating its function as a chalcone isomerase <i>in vivo</i>. In summary, our findings reveal the <i>in vitro</i> as well as <i>in vivo</i> functions of OjCHI and provide a resource to understand the mechanism of anthocyanin biosynthesis in <i>O. japonica</i>.