Abstract
BackgroundThe regulation of anthocyanin biosynthesis by various factors including sugars, light and abiotic stresses is mediated by numerous regulatory factors acting at the transcriptional level. Here experimental evidence was provided in order to demonstrate that the nuclear GARP transcription factor AtGLK1 plays an important role in regulating sucrose-induced anthocyanin biosynthesis in Arabidopsis.ResultsThe results obtained using real-time quantitative PCR and GUS staining assays revealed that AtGLK1 was mainly expressed in the green tissues of Arabidopsis seedlings and could be induced by sucrose. The loss-of-function glk1 glk2 double mutant has lower anthocyanin levels than the glk2 single mutant, although it has been determined that loss of AtGLK1 alone does not affect anthocyanin accumulation. Overexpression of AtGLK1 enhances the accumulation of anthocyanin in transgenic Arabidopsis seedlings accompanied by increased expression of anthocyanin biosynthetic and regulatory genes. Moreover, we found that AtGLK1 also participates in plastid-signaling mediated anthocyanin accumulations. Genetic, physiological, and molecular biological approaches demonstrated that AtGLK1 acts upstream of MYBL2, which is a key negative regulator of anthocyanin biosynthesis, to genetically regulate sucrose-induced anthocyanin biosynthesis.ConclusionOur results indicated that AtGLK1 positively regulates sucrose-induced anthocyanin biosynthesis in Arabidopsis via MYBL2.
Highlights
The regulation of anthocyanin biosynthesis by various factors including sugars, light and abiotic stresses is mediated by numerous regulatory factors acting at the transcriptional level
In order to investigate whether or not the Arabidopsis transcription factor AtGLK1 is involved in responses to sugar signalling, we examined the effects of exogenous sucrose on AtGLK1 expression levels
Our results showed that the overexpression of MYBL2 significantly suppressed the anthocyanin biosynthesis of AtGLK1overexpressing seedlings, which indicated that MYBL2 was epistatic to AtGLK1 in anthocyanin biosynthesis (Fig. 6b-c)
Summary
The regulation of anthocyanin biosynthesis by various factors including sugars, light and abiotic stresses is mediated by numerous regulatory factors acting at the transcriptional level. Anthocyanins are an important class of polyphenols which are characterized with remarkable antioxidant activities Such activities help to protect plants against different abiotic and biotic stress conditions [2,3,4,5]. The gene encoding enzymes required for the anthocyanin biosynthetic pathways are conserved among different plants [6], and can be grouped into the following two classes [7, 8]. In Arabidopsis, the transcription factors PIF3 and HY5 positively regulate anthocyanin biosynthesis by directly binding to the promoters of the anthocyanin biosynthetic genes, including CHS, CHI, F3H, F3′H, DFR, and LDOX [12]. In contrast to the positive transcription factors mentioned above, the R3-MYB protein MYBL2 acts as a transcriptional repressor, and negatively regulates the biosynthesis of anthocyanin [13, 14]. Further studies have revealed that MYBL2 inhibits anthocyanin biosynthesis by interacting with TT8 protein to form a transcriptional inhibitory complex which has the ability to bind to the DFR promoter and inhibit the transcription of the DFR gene [14]
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