A Role for PacMYBA in ABA-Regulated Anthocyanin Biosynthesis in Red-Colored Sweet Cherry cv. Hong Deng (Prunus avium L.)

Abstract

The MYB transcription factors and plant hormone ABA have been suggested to play a role in fruit anthocyanin biosynthesis, but supporting genetic evidence has been lacking in sweet cherry. The present study describes the first functional characterization of an R2R3-MYB transcription factor, PacMYBA, from red-colored sweet cherry cv. Hong Deng (Prunus avium L.). Transient promoter assays demonstrated that PacMYBA physically interacted with several anthocyanin-related basic helix-loop-helix (bHLH) transcription factors to activate the promoters of PacDFR, PacANS and PacUFGT, which are thought to be involved in anthocyanin biosynthesis. Furthermore, the immature seeds of transgenic Arabidopsis plants overexpressing PacMYBA exhibited ectopic pigmentation. Silencing of PacMYBA, using a Tobacco rattle virus (TRV)-induced gene silencing technique, resulted in sweet cherry fruit that lacked red pigment. ABA treatment significantly induced anthocyanin accumulation, while treatment with the ABA biosynthesis inhibitor nordihydroguaiaretic acid (NDGA) blocked anthocyanin production. PacMYBA expression peaked after 2 h of pre-incubation in ABA and was 15.2-fold higher than that of sweet cherries treated with NDGA. The colorless phenotype was also observed in the fruits silenced in PacNCED1, which encodes a key enzyme in the ABA biosynthesis pathway. The endogenous ABA content as well as the transcript levels of six structural genes and PacMYBA in PacNCED1-RNAi (RNA interference) fruit were significantly lower than in the TRV vector control fruit. These results suggest that PacMYBA plays an important role in ABA-regulated anthocyanin biosynthesis and ABA is a signal molecule that promotes red-colored sweet cherry fruit accumulating anthocyanin.

Evaluating the involvement and interaction of abscisic acid and miRNA156 in the induction of anthocyanin biosynthesis in drought-stressed plants

“…For example, Shen et al (2014) reported that treatment of Prunus avium with the ABA biosynthetic inhibitor nordihydroguaiaretic acid (NDGA) downregulated the expression levels of Myeloblastosis A (MYBA), a transcription factor that interacts and activates the promoters of the DFR, ANS, and UFGT genes. These authors also showed that the endogenous ABA levels as well as the transcript levels of CHS, chalcone isomerase (CHI), F3H, DFR, UFGT, and MYBA were blocked by silencing the 9-cis-epoxycarotenoid dioxygenase (NCED) gene, which encodes a key enzyme in the ABA biosynthetic pathway.…”

Abscisic Acid Regulates Anthocyanin Biosynthesis and Gene Expression Associated With Cell Wall Modification in Ripening Bilberry (Vaccinium myrtillus L.) Fruits

“…ABA has been indicated as a ripening promoter in many non-climacteric fruits, such as strawberry (Jia et al, 2011; Li et al, 2011; Kadomura-Ishikawa et al, 2015), grape (Koyama et al, 2010; Jia et al, 2017), sweet cherry (Luo et al, 2014; Shen et al, 2014), cucumber (Wang et al, 2013), citrus (Zhang et al, 2014), pear (Dai et al, 2014), and litchi (Singh et al, 2014) but also for climacteric fruits, such as tomato, peach, melon, and mango (Zhang et al, 2009; Soto et al, 2013; Sun et al, 2013; Zaharah et al, 2013; Mou et al, 2015). The direct molecular level evidence for the role of ABA in fruit ripening was shown in strawberry by suppressing the expression of the key ABA biosynthetic gene, FaNCED1 , blocking ABA biosynthesis and leading to partly uncolored strawberry fruits that could be rescued by exogenous ABA (Jia et al, 2011).…”

Transcriptional regulation of PaPYLs, PaPP2Cs and PaSnRK2s during sweet cherry fruit development and in response to abscisic acid and auxin at onset of fruit ripening

“…Secondly, exogenous ABA application to the sweet cherry fruit at the second rapid growth phase can not only accelerate fruit softening and increase the maturation index levels, but also enhance the fruit quality by increasing the content of total sugar and anthocyanin (Kondo and Gemma 1993;Ren et al 2010). Furthermore, a latest study reported that ABA can directly regulate sweet cherry fruit coloration via affecting the expression level of the PacMYBA which is a transcription factor that interacts with several anthocyanin-related bHLH transcription factors to further activate the promoters of key genes in anthocyanin biosynthesis pathway (Shen et al 2014). Besides the effects on pericarp, ABA can also affect the lignification process thereby regulating the seed development in sweet cherry (Kondo and Inoue 1997).…”

“…Phytohormones, both the endogenous and the synthetic, have been proved to have mass of effects on the development and ripening of many kinds of fruits (Given et al 1988;Zhang et al 2009;Jia et al 2011), including sweet cherry (Shen et al 2014), and at most of the time, their biological functions must depend on the perception of their specific receptors and transduction of their signaling pathways. There are two kinds of ABA signal transduction pathways that have been reported: one is the PYR/PYL/ RCARs (ABA receptor, hereafter the PYLs)-PP2C (ABA signal negative regulators, type 2C protein phosphatases)-SnRK2 (ABA signal positive regulators, subfamily 2 of SNF1-related kinases) pathway, in which the signal transduction depends on the phosphorylation/dephosphorylation of these three core components (Ma et al 2009;Melcher et al 2009;Nishimura et al 2009;Park et al 2009;Umezawa et al 2009): ABA can be sensed and bound by PYLs which belongs to the START protein superfamily through their ligand-binding pockets; with the binding of ABA, PYL closes two highly conserved b-loops around the entry of the ligand-binding pocket and forms a 'cap-lock' interface which in turn binds to PP2C phosphatase activity site and directly inhibits the activity of PP2C; then SnRK2s are released from the dephosphorylating of PP2C and can phosphorylate downstream proteins or transcription factors that trigger the expression of ABA-responsive genes.…”