Abstract
The red color is an attractive trait of fruit and determines its market acceptance. 5-Aminolevulinic acid (ALA), an eco-friendly plant growth regulator, has played a universal role in plant secondary metabolism regulation, particularly in flavonoid biosynthesis. It has been widely reported that ALA can up-regulate expression levels of several structural genes related to flavonoid metabolism and anthocyanin accumulation. However, the molecular mechanisms behind ALA-induced expression of these genes are complicated and still far from being completely understood. In this study, transcriptome analysis identified the differentially expressed genes (DEGs) associated with ALA-induced anthocyanin accumulation. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the flavonoid biosynthesis (ko00941) pathway was significantly enhanced in the ALA-treated apple calli at 24, 48, and 72 h after the treatment. Expression pattern revealed that ALA up-regulated the expression of the structural genes related to not only anthocyanin biosynthesis (MdCHS, MdCHI, MdF3’H, MdDFR, MdANS, and MdUFGT) but also anthocyanin transport (MdGST and MdMATE). Two R2R3-MYB transcription factors (MdMYB10 and MdMYB9), which are the known positive regulators of anthocyanin biosynthesis, were significantly induced by ALA. Gene overexpression and RNA interference assays demonstrated that MdMYB10 and MdMYB9 were involved in ALA-induced anthocyanin biosynthesis. Moreover, MdMYB10 and MdMYB9 might positively regulate the transcription of MdMATE8 by binding to the promoter region. These results indicate that MdMYB10 and MdMYB9 modulated structural gene expression of anthocyanin biosynthesis and transport in response to ALA-mediated apple calli coloration at the transcript level. We herein provide new details regarding transcriptional regulation of ALA-induced color development.
Highlights
Fruit coloration acts as one of the most important factors determining commodity value of red cultivars
It was described that several members of glutathione S-transferase (GST) and the multidrug and toxic compound extrusion (MATE) family were involved in anthocyanin transport, such as Zea mays Bronze2 (Marrs et al, 1995), petunia AN9 (Mueller et al, 2000), Arabidopsis TT12 and TT19 (Debeaujon et al, 2001), and grape AM1 and AM3 (Gomez et al, 2009)
The promotive capacity of acceptance. 5Aminolevulinic acid (ALA) on expression of MdMATE8 was obviously inhibited in ALA-treated MdMYB10 or MdMYB9 RNAi calli, compared with the control(i) + ALA calli. These findings indicate that MdMYB10 and MdMYB9 were probably involved in transcriptional expression regulation of MdMATE8 in ALA-up-regulated anthocyanin accumulation
Summary
Fruit coloration acts as one of the most important factors determining commodity value of red cultivars. A number of flavonoid biosynthesis pathways have been characterized in fruit crops, including apple (Takos et al, 2006), pear (Fischer et al, 2007), grape (Sparvoli et al, 1994), and strawberry (Pillet et al, 2015). With regard to the preliminary mechanism, several studies suggest that ALApromoted anthocyanin accumulation is closely related to higher expression levels of flavonoids biosynthetic genes, including CHS, DFR, ANS, and UFGT (Guo et al, 2013; Xie et al, 2013; Feng et al, 2016; Ye et al, 2017)
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