A coupled role for CsMYB75 and CsGSTF1 in anthocyanin hyperaccumulation in purple tea

Abstract

Cultivars of purple tea (Camellia sinensis) that accumulate anthocyanins in place of catechins are currently attracting global interest in their use as functional health beverages. RNA-seq of normal (LJ43) and purple Zijuan (ZJ) cultivars identified the transcription factor CsMYB75 and phi (F) class glutathione transferase CsGSTF1 as being associated with anthocyanin hyperaccumulation. Both genes mapped as a quantitative trait locus (QTL) to the purple bud leaf color (BLC) trait in F 1 populations, with CsMYB75 promoting the expression of CsGSTF1 in transgenic tobacco (Nicotiana tabacum). Although CsMYB75 elevates the biosynthesis of both catechins and anthocyanins, only anthocyanins accumulate in purple tea, indicating selective downstream regulation. As glutathione transferases in other plants are known to act as transporters (ligandins) of flavonoids, directing them for vacuolar deposition, the role of CsGSTF1 in selective anthocyanin accumulation was investigated. In tea, anthocyanins accumulate in multiple vesicles, with the expression of CsGSTF1 correlated with BLC, but not with catechin content, in diverse germplasm. Complementation of the Arabidopsis tt19-8 mutant, which is unable to express the orthologous ligandin AtGSTF12, restored anthocyanin accumulation, but did not rescue the transparent testa phenotype, confirming that CsGSTF1 did not function in catechin accumulation. Consistent with a ligandin function, transient expression of CsGSTF1 in Nicotiana occurred in the nucleus, cytoplasm and membrane. Furthermore, RNA-Seq of the complemented mutants exposed to 2% sucrose as a stress treatment showed unexpected roles for anthocyanin accumulation in affecting the expression of genes involved in redox responses, phosphate homeostasis and the biogenesis of photosynthetic components, as compared with non-complemented plants.

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.…”

Transcriptomic and metabolomic analysis provides insights into anthocyanin and procyanidin accumulation in pear

“…Plant GSTs are encoded by a large gene family, and are soluble and abundant in the cytosol [26,50,51]. They can be divided into eight subgroups, among which the tau and phi classes play key roles in flavonoid transport [52]. Bronze 2 (bz2) in maize was the first tau class GST reported to be involved in anthocyanin accumulation; bz2 produces yellow skin kernels because of disabled anthocyanin transport into the vacuole [53].…”

“…Bronze 2 (bz2) in maize was the first tau class GST reported to be involved in anthocyanin accumulation; bz2 produces yellow skin kernels because of disabled anthocyanin transport into the vacuole [53]. Anthocyanin deposition is also affected by genes in the phi class, such as AtGSTF12 in Arabidopsis [54,55], FvRAP in strawberry [26], CsGSTF1 in tea [52], and VvGST4 in grapevine [56]. Interestingly, these phi-class GSTs show extensive functional diversification.…”

“…Interestingly, these phi-class GSTs show extensive functional diversification. For example, AtGSTF12 plays a key role in both anthocyanin and PA accumulation in Arabidopsis [54], while CsGSTF1 in tea functions only in anthocyanin accumulation [52]. Functional divergence of GSTs has arisen through nonsynonymous mutations, especially at key amino acid sites [51].…”