A Functional InDel in the WRKY10 Promoter Controls the Degree of Flesh Red Pigmentation in Apple.

MYB transcription factors have been linked to anthocyanin synthesis and various color phenotypes in plants. In apple, MYB10 confers a red-flesh phenotype due to a minisatellite insertion in its R6 promoter, but R6:MYB10 genotypes exhibit various degrees of red pigmentation in the flesh, suggesting the involvement of other genetic factors. Here, it is shown that MdWRKY10, a transcription factor identified via DNA pull-down trapping, binds to the promoter of MdMYB10 and activates its transcription. MdWRKY10 specifically interacts with the WDR protein MdTTG1 to join the apple MYB-bHLH-WDR (MBW) complex, which significantly enhances its transcriptional activation activity. A 163-bp InDel detected in the promoter region of the alleles of MdWRKY10 in a hybrid population of identical heterozygous genotypes regarding R6 by structural variation analysis, contains a typical W-box element that MdWRKY10 binds to for transactivation. This leads to increased transcript levels of MdWRKY10 and MdMYB10 and enhanced anthocyanin synthesis in the flesh, largely accounting for the various degrees of flesh red pigmentation in the R6 background. These findings reveal a novel regulatory role of the WRKY-containing protein complex in the formation of red flesh apple phenotypes and provide broader insights into the molecular mechanism governing anthocyanin synthesis in plants.

The ABA-induced NAC transcription factor MdNAC1 interacts with a bZIP-type transcription factor to promote anthocyanin synthesis in red-fleshed apples.

Anthocyanins are valuable compounds in red-fleshed apples. The MdMYB10 transcription factor is an important regulator of the anthocyanin synthesis pathway. However, other transcription factors are key components of the complex network controlling anthocyanin synthesis and should be more thoroughly characterized. In this study, we used a yeast-based screening technology to identify MdNAC1 as a transcription factor that positively regulates anthocyanin synthesis. The overexpression of MdNAC1 in apple fruits and calli significantly promoted the accumulation of anthocyanins. In binding experiments, we demonstrated that MdNAC1 combines with the bZIP-type transcription factor MdbZIP23 to activate the transcription of MdMYB10 and MdUFGT. Our analyses also indicated that the expression of MdNAC1 is strongly induced by ABA because of the presence of an ABRE cis-acting element in its promoter. Additionally, the accumulation of anthocyanins in apple calli co-transformed with MdNAC1 and MdbZIP23 increased in the presence of ABA. Therefore, we revealed a novel anthocyanin synthesis mechanism involving the ABA-induced transcription factor MdNAC1 in red-fleshed apples.

Mdm-miR858 targets MdMYB9 and MdMYBPA1 to participate anthocyanin biosynthesis in red-fleshed apple.

Anthocyanins are important secondary metabolites in plants. They are important for human health because of their antioxidant activities and because their dietary intake reduces the incidence of cardiovascular and cerebrovascular diseases and tumors. The biosynthesis of anthocyanins and its regulation in fruits and vegetables is a global research hotspot. Compared with cultivated apples, the red-fleshed apple is a relatively new and popular commodity in the market. Previous studies on red-fleshed apples have focused on the basis for the high anthocyanin content and the transcriptional regulation of anthocyanin synthesis. In the present study, we focused on the mechanism of microRNA-mediated post-transcriptional regulation of anthocyanin synthesis in red-fleshed apples. We identified a microRNA (miRNA), designated mdm-miR858, that is specifically expressed in the flesh of apple fruit. The expression level of miR858 was significantly lower in red-fleshed apples than in white-fleshed apples. The overexpression of mdm-miR858 significantly inhibited anthocyanin accumulation, whereas the silencing of mdm-miR858 promoted anthocyanin synthesis in STTM858 transgenic apple calli. Further analyses showed that mdm-miR858 targets the transcription factor genes MdMYB9 and MdMYBPA1 to participate anthocyanin accumulation in apple. Our results also show that MdHY5, a transcription factor in the light signaling pathway, can bind to the promoter of mdm-miR858 to inhibit its transcription, thereby regulating anthocyanin synthesis. Based on our results, we describe a novel HY5-miR858-MYB loop involved in the modulation of anthocyanin biosynthesis. These findings provide new information about how plant miRNAs regulate anthocyanin anabolism and provide a basis for breeding new anthocyanin-rich, red-fleshed apple varieties.

Analyses of the photosynthetic characteristics, chloroplast ultrastructure, and transcriptome of apple (Malus domestica) grown under red and blue lights.

BACKGROUND: Light quality significantly affects plant growth and development, photosynthesis, and carbon and nitrogen metabolism. Apple (Malus domestica Borkh.) is a widely cultivated and economically important fruit crop worldwide. However, there are still few studies on the effects of different light qualities on the growth and development of apple seedlings. RESULTS: In this study, we explored the effects of blue and red light treatments on the growth and development, photosynthetic characteristics, leaf chloroplast ultrastructure, and carbon and nitrogen metabolism of apple seedlings. Blue light significantly inhibited apple plant growth and leaf extension, but it promoted the development of leaf tissue structures and chloroplasts and positively affected leaf stomatal conductance, the transpiration rate, and photosynthetic efficiency. The red light treatment promoted apple plant growth and root development, but it resulted in loosely organized leaf palisade tissues and low chlorophyll contents. The blue and red light treatments enhanced the accumulation of ammonium nitrogen in apple seedlings. Moreover, the blue light treatment significantly promoted nitrogen metabolism. Additionally, an RNA-seq analysis revealed that both blue light and red light can significantly up-regulate the expression of genes related to carbon and nitrogen metabolism. Blue light can also promote amino acid synthesis and flavonoid metabolism, whereas red light can induce plant hormone signal transduction. The expression of a gene encoding a bHLH transcription factor (MYC2-like) was significantly up-regulated in response to blue light, implying it may be important for blue light-mediated plant development. CONCLUSIONS: Considered together, blue and red light have important effects on apple growth, carbon and nitrogen metabolism. These findings may be useful for determining the ideal light conditions for apple cultivation to maximize fruit yield and quality.