A white mutant of Malay apple fruit (Syzygium malaccense) lacks transcript expression and activity for the last enzyme of anthocyanin synthesis, and the normal expression of a MYB transcription factor.

摘要

Peel of mature Malay apple is initially glossy red and then changes to purple. A mutant with mature fruits and white peel is described. Peel of wild-type fruits contained 5 glucose-based anthocyanins (cyanidin-3-O-glucoside, pelargonidin-3-O-glucoside, peonidin-3-O-glucoside, cyanidin-3,5-O-diglucoside, peonidin-3,5-O-diglucoside). Cyanidin-3-O-glucoside accounted for a large proportion of the total anthocyanins content. Accumulation cyanidin-3-O-glucoside during fruit maturation was correlated with increased activities of phenylalanine ammonia lyase (PAL) and UDPglucose:flavonoid 3-O-glucosyltransferase (UF3GlucT, F3GT). In wild-type peel, transcripts of 7 genes that encode enzymes in the anthocyanins biosynthetic pathway were detected. No anthocyanins were found in white mutant peel. Peel of white mutant fruits contained transcripts of all 7 genes identified, except F3GT. It also showed no F3GT activity. Results suggest that the lack of anthocyanins in the mutant was due to a lack of F3GT expression. In addition, the transcript of a MYB transcription factor, highly homologous to 3 Arabidopsis MYB involved in anthocyanins synthesis, was virtually absent in the mutant but very high in wild-type fruits. It is suggested that the lack of MYB expression is part of the cause of the lack of F3GT expression and anthocyanins synthesis during fruit maturation.