Differential anthocyanin accumulation in radish taproot: importance of RsMYB1 gene structure
RsMYB1a was the crucial MYB, and RsbHLH4 is the essential partner in regulating the anthocyanin biosynthesis in radish.
There are four color types of radish according to whether or not the anthocyanin accumulates in the skin and flesh of taproot. Red radishes accumulate a substantial amount of anthocyanins in both the skin and flesh. It is well known that the MYB-bHLH-WD40 transcription factor(s) complex regulates the biosynthesis of anthocyanin in plants. Here in, four candidate MYB and bHLH genes, RsMYB1a, RsMYB1b, RsbHLH2 and RsbHLH4, were isolated from red radish ‘Hongxin 1’. The expression of RsbHLH4 and the two structural genes RsANS and RsUFGT was significantly positively correlated with anthocyanin contents. The expression of RsMYB1a was also highly correlated with anthocyanin accumulation, particularly when the white flesh sample of ‘Hongxin 1-1’ was excluded. The transient expression of RsMYB1a in the radish cotyledon and leaf induced anthocyanin accumulation with even stronger promoting role when expression in combination with RsbHLH4. These results suggested that RsMYB1a was the crucial MYB, and that RsbHLH4 is an essential partner in regulating the biosynthesis of anthocyanins in radish. The low or undetectable RsbHLH4 expression paralleled the lack of anthocyanin accumulation in the white flesh of ‘Hongxin 1-1’ and ‘Shaguan 1’. Assays demonstrated that RsMYB1a interacted with RsbHLH4 and activated the expression of RsbHLH4. Notably, all the dark red radish cultivars have a longer RsMYB1a genomic DNA sequence, while the short and nonfunctional RsMYB1a is present in non-red cultivars. The length of the first intron and the presence of an early stop codon of RsMYB1 might underlie the differential anthocyanin accumulation in the radish taproot.
KeywordsRed radish Anthocyanins MYB bHLH Transcriptional regulation
4-Coumarate CoA ligase
Bimolecular fluorescence complementation
Open read frame
Phenylalanine ammonia lyase
Quantitative real-time PCR
Yellow fluorescence protein
This study was supported in part by Scientific and Technological Research Program of Chongqing Municipal Education Commission (Grant nos. KJ1712303 and KJ1712302), Chongqing Natural Science Foundation (Grant nos. cstc2017jcyjA0001, cstc2016jcyjA0136 and cstc2017shms-xdny80074) and Yangtze Normal University (Grant nos. 2016KYQD20 and 2016XJQN06).
Author contribution statement
BL and LND designed the study. BL, YYC, HL, QW, CLW, and RS carried out the experiments. BL and LND analyzed the data. FBC sampled the red radishes. BL, LND and HCW wrote the manuscript. All the authors read and agreed to submit the manuscript.
Compliance with ethical standards
Conflict of interest
All the authors declare no conflict of interest.
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