Identification and functional characterization of lycopene β-cyclase gene from Iris germanica and its relation to...

Accumulations of pigments plays a pivotal role in determining floral coloration, which constitutes one of the most critical ornamental characteristics in flowering plants. In Iris germanica, carotenoids underlie yellow, orange and pink flowers, yet comprehensive metabolomic profiling and associated gene regulatory networks in carotenoid biosynthetic pathway remain to be elucidated. In this study, the carotenoids and transcriptome profiles of yellow, orange and pink flower cultivars were analyzed. In pink flower 'Lenora Pearl' and orange flower 'Savannah Sunset', lycopene and (E/Z)-phytoene were the major pigments. In yellow flower 'Harvest of Memories' and 'Little Miss Magic', antheraxanthin, β-cryptoxanthin and violaxanthin were the major pigments. The expression profiles of structural genes in the carotenoid pathway were analyzed among different flower-colored cultivars. Among the structural genes, IgLCYB2s expression positively correlation with β, β-carotene (β-carotene and its derivatives) biosynthesis while negatively correlating with lycopene accumulation across cultivars, these pattern also consistent with flower color phenotype among cultivars. Thus, IgLCYB2s could be the critical genes determine composition and content of carotenoids among different cultivars. Quantitative real-time PCR results revealed that IgLCYB2s were tissue-specific in flowers. Enzyme activity assays in Escherichia coli indicated IgLCYB2s converted lycopene into β-carotene in vivo, which confirmed the function of IgLCYB2 as structural gene in regulation the composition of carotenoids. In future, IgLCYB2s can be used in genetic manipulations to facilitate genetically modified breeding of flower color in I. germanica or iris genus.