Full-Length Transcriptome Analysis and Characterization of DFRs Involved in the Formation of Anthocyanin in Allium wallichii

Allium wallichii is famous for its reddish-purple flowers, which can be utilized as cut flowers and garden landscaping. Flower color is mainly determined by flavonoids, betalains, carotenoids, as well as other pigments. However, there is no research on the color formation mechanism in A. wallichii, which restricts its genetic improvement and development of superior varieties. The flower of A. wallichii was collected for full-length transcriptome sequencing and metabolome analysis using PacBio SMART and UPLC-MS, respectively. A total of 45 anthocyanins were detected in its flower, and 75,778 transcripts of 107,208 non-redundant transcripts were annotated. Then, two AwDFRs were cloned and characterized using bioinformatics tools. Enzyme activity assays revealed that both AwDFR1 and AwDFR2 possessed DFR activity in vitro that only accepted DHQ and DHM as substrates, except for DHK. Finally, physiological results showed that AwDFR1 and AwDFR2 could restore the lacking phenotypes of Arabidopsis tt3 mutant and increase the content of anthoycanin in tobacco petals. The anthocyanins and transcriptome in A. wallichii were firstly reported, and AwDFR1 and AwDFR2 are key enzymes participating in the biosynthesis of anthocyanins. This research provides important guidance for future key gene mining, color improvement, and horticultural breeding in A. wallichii.