MdGSTF6, activated by MdMYB1, plays an essential role in anthocyanin accumulation in apple

Abstract

Anthocyanins are biosynthesized on the cytosolic surface of the endoplasmic reticulum and then transported into the vacuole for storage. Glutathione S -transferases (GSTs) are considered to be responsible for the transport of anthocyanins into the vacuole. However, the regulatory mechanisms of GSTs in plants are still unclear. Here, we performed a genome-wide analysis and identified 69 GST genes in apple. The expression of MdGSTF6 was positively correlated with the anthocyanin content ( r = 0.949) during ‘Yanfu 8’ fruit development. The overexpression of MdGSTF6 in the Arabidopsis thaliana tt19 mutant resulted in seedlings of 35S:: MdGSTF6 -GFP/ tt19 that could accumulate anthocyanin and rescue its phenotype, suggesting that MdGSTF6 was an anthocyanin transporter. The silencing of MdGSTF6 affected anthocyanin accumulation in apple fruit. Moreover, the knockdown of MdGSTF6 by RNA interference in cultured ‘Gala’ seedlings inhibited anthocyanin accumulation. The interaction experiments showed that MdMYB1 could bind directly to the MdGSTF6 promoter to transcriptionally activate its expression. Collectively, our results demonstrate that MdGSTF6 encodes an important GST transporter of anthocyanins in apple fruit and provide evidence for the associated regulatory mechanisms. Therefore, MdMYB1 can not only regulate anthocyanin synthesis, but also control the transport of anthocyanin in apples. This information may be useful for further clarifying the regulation of anthocyanin transport in apple.

PpGST1, an anthocyanin‐related glutathione S‐transferase gene, is essential for fruit coloration in peach

“…Earlier work in litchi revealed that the expression of LcGST4 was also activated by LcMYB1 (Hu et al, 2016). Similar results were also reported in strawberry, apple, tea and kiwifruit (Jiang et al, 2019;Liu et al, 2019;Luo et al, 2018;Wei et al, 2019). Data from the dual-luciferase assays performed in this study suggested that the transcriptional activity of the PpGST1 promoter is directly up-regulated by PpMYB10.1 rather than PpMYB10.2 and PpMYB10.3, and it was further activated by PpbHLH3 through the interaction between PpMYB10.1 and PpbHLH3.…”

“…Heterologous overexpression of VviGST4 ( Vitis vinifera ) and AcGST1 ( Actinidia chinensis ) in Arabidopsis tt19 mutant can functionally complement both the anthocyanin‐less phenotype in plant and the PA‐deficient phenotype in seed coat (Liu et al , ; Pérez‐Díaz et al , ). However, in this study, PpGST1 only possessed the capacity to functionally complement the anthocyanin‐less phenotype of Arabidopsis tt19 mutant but not the PA‐deficient phenotype in the seed coat, which was similar to the result of An9 ( Petunia hybrida ), LcGST4 ( Litchi chinensis ), RAP ( Fragaria ananassa ), CsGSTF1 ( Camellia sinensis ) and MdGSTF6 ( Malus domestica ) in the tt19 complementation assay (Hu et al , ; Jiang et al , ; Kitamura et al , ; Luo et al , ; Wei et al , ). These data indicated that PpGST1 plays a pivotal role in anthocyanin transport and differed from AtTT19 , VviGST4 and AcGST1 which also participate in seed deposition of PAs.…”

“…GSTs comprise a ubiquitous complex gene family in plants with the function to catalyse glutathionylation in a covalent form and serve as nonenzymatic carrier protein for endogenous compounds that require compartmentalization (Conn et al, 2008;Marrs et al, 1995). The involvement of GSTs in trafficking and accumulation of anthocyanins have been verified in maize (Marrs et al, 1995), petunia (Mueller et al, 2000), Arabidopsis (Sun et al, 2012), cyclamen (Kitamura et al, 2012), perilla , grape (Conn et al, 2008), apple (Jiang et al, 2019) and litchi (Hu et al, 2016). In this study, we found a GST (PpGST1), with GeneID (Prupe.3G013600, also previously as ppa011307m) later found to be identical to that of an anthocyanin transporter (Riant) related to the variegated coloration of peach flowers (Cheng et al, 2015), was differentially expressed in 'HJ' and 'YL' throughout developmental stages, which may account for the distinct anthocyanin accumulation in the fruit of two cultivars.…”

“…MdGSTF6 was shown to be the functional member in anthocyanin sequestration in apple fruit (Jiang et al, 2019).…”

“…In grapevine, VviGST3 is related to PA transport while VviGST4 is pivotal for both anthocyanin and PA accumulation (Pérez‐Díaz et al , ). MdGSTF6 was shown to be the functional member in anthocyanin sequestration in apple fruit (Jiang et al , ).…”