Two inactive MdMYBl alleles were transcribed during UV-B-induced coloration of 'Mutsu' apple

摘要

It has been well known that a class of R2R3-MYB genes is involved in anthocyanin accumulation in plants. In apple, MdMYBl/A/10 is considered as a key regulatory factor that contributes to the red coloration of fruit skin. For MdMYBl/A, at least threealleles {MdMYBl-1, MdMYBl-2 and MdMYBl-3) have been identified from different apple cultivars, among which only MdMYBl-1 is a functional allele, while MdMYBl-2 and MdMYBl-3 are not. Accordingly, 'Mutsu', a triploid apple cultivar whose MYB1 alleles are MdMYBl-2/MdMYBl-2/ MdMYBl-3, retains green under natural light condition. However, 'Mutsu' also turns to red/ pink when cultivated by paper-bagging treatment during fruit development followed by exposure to natural light or artificial UV-B. This phenomenon was also observed in some other yellow/green cultivars lack in functional MdMYBl-1, such as 'Orin' and 'Kinsei'. In this work, we intended to figure out the reason for red coloration of 'Mutsu' by paper-bagging despite lack in functional MdMYBl-1 allele. In our previous report, high level of MdMYBl transcripts were detected by qRT-PCR in colorized fruit skin of 'Mutsu'. This work investigated which MdMYBl alleles were transcribed in the red fruit skin. As a result, transcripts of both MdMYBl-2 and MdMYBl-3 were detected. Along with the transcription of MdMYBl, expressions of anthocyanin biosynthesis-related genes, such aschalcone synthase, anthocyanin synthase and UDP-galactose transferase genes were also observed.