Carnation <i>I</i> locus contains two chalcone isomerase genes involved in orange flower coloration

Abstract

Carnations carrying a recessive I gene show accumulation of the yellow pigment chalcononaringenin 2′-glucoside (Ch2′G) in their flowers, whereas those with a dominant I gene do accumulation the red pigment, anthocyanin. Although this metabolic alternative at the I gene could explain yellow and red flower phenotypes, it does not explain the development of orange flower phenotypes which result from the simultaneous accumulation of both Ch2′G and anthocyanin. The carnation whole genome sequencing project recently revealed that two chalcone isomerase genes are present, one that is consistent with the I gene (Dca60979) and another (Dca60978) that had not been characterized. Here, we demonstrate that Dca60979 shows a high level of gene expression and strong enzyme activity in plants with a red flower phenotype; however, functional Dca60979 transcripts are not detected in plants with an orange flower phenotype because of a dTdic1 insertion event. Dca60978 was expressed at a low level and showed a low level of enzyme activity in plants, which could catalyze a part of chalcone to naringenin to advance anthocyanin synthesis but the other part remained to be catalyzed chalcone to Ch2′G by chalcone 2′-glucosyltransferase, resulting in accumulation of anthocyanin and Ch2′G simultaneously to give orange color.

The Evolution of Flavonoid Biosynthesis: A Bryophyte Perspective

“…Studies on mutants for chi in Arabidopsis (tt5), carnation (i), and rice (gh1) found that flavonoid biosynthesis was not fully prevented (Stich et al, 1992;Hong et al, 2012;Jiang et al, 2015), suggesting some spontaneous conversion. However, in the case of carnation at least, the residual production of flavanones in the chi mutant has been found to be due to a second, weakly expressed, CHI gene (Miyahara et al, 2018). Thus, how flavonoid biosynthesis occurs in mosses is an open question.…”

The Chalcone Isomerase Family in Cotton: Whole-Genome Bioinformatic and Expression Analyses of the Gossypium barbadense L. Response to Fusarium Wilt Infection

“…The accumulation patterns of the Ophiorrhiza japonica CHI gene (OjCHI) is consistent across different tissues and developmental stages, indicating its potential role in anthocyanin biosynthesis [10]. Recently, the whole-genome sequencing project of carnation revealed two chalcone isomerase genes (Dca60979 and Dca60978) involved in the coloration of orange flowers [11]. More recent investigations suggested an involvement of CHI genes in the abiotic stress responses and biotic stress responses.…”

Analysis of Flower Color Variation in Carnation (<i>Dianthus caryophyllus</i> L.) Cultivars Derived from Continuous Bud Mutations

“…Thus, we isolated two CHI genes from the petals of three cultivars in the "MINAMI series" with the reference of Carnation DB. In Carnation DB, CHI1 (Dca60979) localized close to CHI2 (Dca60978) on the same scaffold 94 (Miyahara et al, 2018). 'Poly Minami' had two types of CHI, CHI1 coding an inactive enzyme caused by the footprint as mentioned above and CHI2 coding an active enzyme (Figs.…”