MYB_SH[AL]QKY[RF] transcription factors MdLUX and MdPCL-like promote anthocyanin accumulation through DNA hypomethylation and MdF3H activation in apple

Abstract

Heritable DNA methylation is a highly conserved epigenetic mark that is important for many biological processes. In a previous transcriptomic study on the fruit skin pigmentation of apple (Malus domestica Borkh.) cv. ‘Red Delicious’ (G0) and its four continuous-generation bud sport mutants including ‘Starking Red’ (G1), ‘Starkrimson’ (G2), ‘Campbell Redchief’ (G3) and ‘Vallee spur’ (G4), we identified MYB transcription factors (TFs) MdLUX and MdPCL-like involved in regulating anthocyanin synthesis. However, how these TFs ultimately determine the fruit skin colour traits remain elusive. Here, bioinformatics analysis revealed that MdLUX and MdPCL-like contained a well-conserved motif SH[AL]QKY[RF] in their C-terminal region and were located in the nucleus of onion epidermal cells. Overexpression of MdLUX and MdPCL-like in ‘Golden Delicious’ fruits, ‘Gala’ calli and Arabidopsis thaliana promoted the accumulation of anthocyanin, whereas MdLUX and MdPCL-like suppression inhibited anthocyanin accumulation in ‘Red Fuji’ apple fruit skin. Yeast one-hybrid assays revealed that MdLUX and MdPCL-like may bind to the promoter region of the anthocyanin biosynthesis gene MdF3H. Dual-luciferase assays indicated that MdLUX and MdPCL-like activated MdF3H. The whole-genome DNA methylation study revealed that the methylation levels of the mCG context at the upstream (i.e., promoter region) of MdLUX and MdPCL-like were inversely correlated with their mRNA levels and anthocyanin accumulation. Hence, the data suggest that MYB_SH[AL]QKY[RF] TFs MdLUX and MdPCL-like promote anthocyanin biosynthesis in apple fruit skins through the DNA hypomethylation of their promoter regions and the activation of the structural flavonoid gene MdF3H.

Role of core structural genes for flavonoid biosynthesis and transcriptional factors in flower color of plants

“…DhK is an essential precursor for the synthesis of anthocyanin. hence, the F3H gene plays an important role in the color development of plants [55]. The relevant gene of F3H was cloned from the snapdragon for the first time [56].…”

Hypermethylation in the promoter regions of flavonoid pathway genes is associated with skin color fading during ‘Daihong’ apple fruit development

“…Regarding the promoter methylation of genes encoding MYB transcription factors, we observed a negative correlation between promoter methylation and gene expression levels in MdMYBPA1 and MdMYB1R1-like . In addition, the use of ‘Red Delicious’ and its derivative four-generation mutants revealed that the CG methylation level of the novel MYB transcription factors MdPCL-like and MdLUX was negatively associated with their expression levels and anthocyanin content [ 53 ]. Overall, our findings support the notion that DNA methylation plays a vital role in manipulating gene expression and anthocyanin biosynthesis.…”

Meta-Analysis of the Effect of Overexpression of MYB Transcription Factors on the Regulatory Mechanisms of Anthocyanin Biosynthesis

“…Compared with a stable expression system, transient transformation provides an efficient, convenient and faster tool to analyze gene function ( Wroblewski et al, 2005 ; Liao et al, 2019 ). To date, transient expression of MYBs has been well characterized in anthocyanidin biosynthesis of various plants, including rose ( Rosa hybrida ), radish ( Raphanus sativus ), freesia ( Freesia hybrida ), gerbera ( Gerbera hybrida ), apple ( Malus domestica ), tobacco ( Nicotiana tabacum ) and others ( Shen et al, 2019 ; Fan et al, 2020 ; Li T. et al, 2020 ; Li Y. et al, 2020 , Li et al, 2021 ; Zhong et al, 2020 ). In our studies, transient expression assays were undertaken in a dataset (105 studies) to test the function of MYB TFs.…”