Overexpression of Ps-CHI1, a homologue of the chalcone isomerase gene from tree peony (Paeonia suffruticosa), reduces the intensity of flower pigmentation in transgenic tobacco

Abstract

Chalcone isomerase (CHI) is one of the key enzymes in the flavonoid and anthocyanin biosynthesis pathway catalyzing the stereospecific isomerization of chalcones into their corresponding (2S)-flavanones. In this study, to investigate the role of CHI in tree peony flower coloration mechanism, a CHI gene was isolated from Paeonia suffruticosa cv. Guan Shi Mo Yu, and designated as Ps-CHI1. The cDNA sequence of Ps-CHI1 was 924 bp in full length containing an opening reading frame of 654 bp that encoded a peptide of 217 amino acids with a predicted molecular mass of 23.3 kDa and a pI of 5.0. Sequence alignment and phylogenetic analysis revealed that Ps-CHI1 shared high homology with other type I higher plant CHI proteins. Quantitative real-time PCR analysis indicated that Ps-CHI1 showed the highest transcript abundance in petals, moderate levels in sepals, low levels in leaves and carpels and the lowest levels in stamens. Ps-CHI1 was expressed at the highest level in early stage of uncolored flowers and underwent moderate decreases in expression until there was little transcription could be detected when flowers fully opened and deeply pigmented. By inserting Ps-CHI1 into tobacco (Nicotiana tabacum L.) via Agrobacterium-mediated transformation, T1 transgenic plants were obtained. Phenotypes and pigment analysis revealed that they produced up to threefold total flavonols and flavones over wild-type control, and showed a remarkable reduction in anthocyanin content and flower color intensity. These results provide theoretical deduction supporting Ps-CHI1 as an important gene involved in tree peony flower pigmentation.