Abstract:Iris hollandica is an important ornamental bulbous plant. In this study, to elucidate molecular mechanism of coloration, as well as anthocyanin accumulation in blue and mutant purple flowers, we used blue wild type ‘Zhanchi’ and purple mutant ‘Ziyun’ as materials to analyze flower color variation by anthocyanin determination, transcriptome sequencing and qRTPCR. The results show that: (1) the total anthocyanin content of purple mutant ‘Ziyun’ in inner tepals (392.7 μg· g-1) was significantly lower than that of wild type ‘Zhanchi’ (543.5 μg· g-1). Compared with ‘Zhanchi’, the content of three anthocyanins in ‘Ziyun’ significantly decreased [The content of cyanidin3rutinoside decreased from 144.42 to 46.39 μg· g-1 . The content of petuniacin3 (6rhamnosyl2xylosylglucoside) decreased from 61.86 to 31.67 μg· g-1. The content of Cyanidin 3(2Gxylosylrutinoside) decreased from 25.22 to 7.65 μg· g-1]. However, the content of 6hydroxycyanidin3glucoside increased from 5.88 to 10.34 μg· g-1. (2) RNAseq analysis revealed that a total of 46 530 unigenes were obtained, compared with ‘Zhanchi’, ‘Ziyun’ had 43 upregulated genes and 73 downregulated genes. Hierarchical cluster analysis showed that there were two differentially expressed genes in the anthocyanin pathway: chalcone synthase (CHS) gene (IhCHS1) and anthocyanin 3O glucose transferase (UFGT) gene (IhUFGT1), and both of them were down regulated. (3) qRTPCR showed that, the expression of IhUFGT1 increased in both varieties with the development of flowers, and reached the highest in early flowering period, and the expression in ‘Ziyun’ flower was significantly lower than that in ‘Zhanchi’. According to the study, significant change of four anthocyanin content may be the main reason for flower color change from wild type ‘Zhanchi’ to mutant ‘Ziyun’. The expression level of IhUFGT1 in purple ‘Ziyun’ flower was significantly lower than that in ‘Zhanchi’, which resulted in the change of anthocyanin content, and finally led to the change of flower color from blue purple to purple.