Biochemical and Molecular Characterization of the Rice Chalcone Isomerase Family

Abstract

Chalcone isomerase (CHI) is a key enzyme in flavonoid biosynthesis. In plants, CHIs occur in multigene families, and they are divided into four types, types I–IV. Type I and II CHIs are bona fide CHIs with CHI activity, and type III and IV CHIs are non-catalytic members with different functions. Rice contains seven CHI family genes (OsCHIs). Molecular analysis suggested that OsCHI3 is a type I CHI, and the other OsCHIs were classified into types III and IV. To elucidate their biochemical functions, OsCHI1, OsCHI3, OsCHI6, and OsCHI7 were expressed in Escherichia coli, and the recombinant OsCHI proteins were purified. An activity assay of recombinant OsCHIs showed that OsCHI3 catalyzed the isomerization of naringenin chalcone and isoliquiritigenin, whereas the other recombinant OsCHIs had no CHI activity. OsCHI3 also exhibited a strong preference to naringenin chalcone compared to isoliquiritigenin, which agrees well with the catalytic properties of type I CHIs. These results ascertain OsCHI3 to be a bona fide CHI in rice. OsCHI3 and the other OsCHIs were expressed constitutively throughout the rice growth period and different tissues. OsCHI3 expression was induced immediately in response to ultra-violet (UV) stress, suggesting its involvement in the biosynthesis of sakuranetin, a flavonoid phytoalexin in rice.

Genome-Wide Classification and Evolutionary Analysis Reveal Diverged Patterns of Chalcone Isomerase in Plants

“…Functional diversification after gene expansion could occur at the transcriptional level. To date, 12 differentially expressed CHIs in G. max [ 25 ], 5 tissue-specific CHIs in A. thaliana [ 15 ], 33 CHIs in cotton [ 32 ], 7 CHIs in rice [ 33 , 34 ], 30 CHIs in six Citrus species [ 35 ], 31 CHIs in liverwort and Selaginella species [ 18 ], 56 CHIs in fern species [ 26 ], and 11 CHIs in D. cambodiana [ 36 ], have been reported. These observations showed that CHIs usually have tissue-specific expression in various tissues, and often respond to various environmental stressors.…”

“…With the sequencing of plant genomes and transcriptomes, more and more plant CHI family genes have been discovered from many species, including primitive seedless plants and higher seed plants. To date, 12 CHIs in Glycine max [ 25 ], 5 CHIs in Arabidopsis thaliana [ 15 ], 33 CHIs in cotton [ 32 ], 7 CHIs in Oryza sativa [ 33 , 34 ], 30 CHIs in six Citrus species [ 35 ], 31 CHIs in liverwort and Selaginella species [ 18 ], 56 CHIs in fern species [ 26 ], and 11 CHIs in Dracaena cambodiana [ 36 ], have been identified based on their corresponding genomic or transcriptomic data. Acquisition of CHI enzymatic activity in plants during evolution is an intriguing topic, because both type III and type IV CHIs are devoid of bona fide CHI catalytic activity.…”

Two Important Anticancer Mechanisms of Natural and Synthetic Chalcones

“…Flavonoids are biosynthesized by phenylpropanoid, starting from phenylalanine [ 61 ]. Chalcone synthetase is the first enzyme in flavonoid biosynthesis and catalyzes the formation of chalcones from one molecule of p-coumaroyl-CoA and three molecules of malonyl-CoA [ 62 ]. Depending on the degree of oxidation of the central nucleus, flavonoids are classified into flavones, flavanones, flavonols (proanthocyanidins), dihydroflavonols, isoflavones, isoflavanones, chalcones, aurones, anthocyanidins and tannins ( Supplementary Figure S1 ) [ 63 , 64 , 65 , 66 ].…”

Gene Co-Expression Network Tools and Databases for Crop Improvement

“…CHS is known to catalyse the first step in the flavonoid biosynthetic pathway to produce naringenin chalcone [60]. Next, CHI catalyses the isomerisation of chalcones into (2S)-flavanones that serve as the precursor to various flavonoids in plants [61]. Rice and maize are monocots containing CHS and CHI gene families from their genomes.…”

“…precursor to various flavonoids in plants [61]. Rice and maize are monocots containing CHS and CHI gene families from their genomes.…”