Abstract
Nitrogen is an important factor that affects plant anthocyanin accumulation. In apple, the nitrate-responsive BTB/TAZ protein MdBT2 negatively regulates anthocyanin biosynthesis. In this study, we found that MdBT2 undergoes posttranslational modifications in response to nitrate deficiency. Yeast two-hybrid, protein pull-down, and bimolecular fluorescence complementation (BiFC) assays showed that MdBT2 interacts with MdGRF11, a 14-3-3 protein; 14-3-3 proteins compose a family of highly conserved phosphopeptide-binding proteins involved in multiple physiological and biological processes. The interaction of MdGRF11 negatively regulated the stability of the MdBT2 protein via a 26S proteasome-dependent pathway, which increased the abundance of MdMYB1 proteins to activate the expression of anthocyanin biosynthesis-related genes. Taken together, the results demonstrate the critical role of 14-3-3 proteins in the regulation of nitrate deficiency-induced anthocyanin accumulation. Our results provide a novel avenue to elucidate the mechanism underlying the induction of anthocyanin biosynthesis in response to nitrate deficiency.
Highlights
As sessile organisms, plants produce multiple secondary metabolites to cope with environmental stresses through sophisticated regulatory mechanisms[1]
The expression of structural genes (UF3GT, ANS, DFR, F3H, CHI, and CHS) involved in anthocyanin biosynthesis is coordinately mediated by the MBW transcription complex, which is composed of three types of transcription factors (TFs): basic helix-loop-helix, R2R3-MYB, and WD40-repeat proteins[10]
The results showed that the His-MdGRF11 protein was pulled down only by glutathione S-transferase (GST)-MdBT2 and not by the GST control (Fig. 2c), demonstrating that MdGRF11 interacted with MdBT2 in vitro
Summary
Plants produce multiple secondary metabolites to cope with environmental stresses through sophisticated regulatory mechanisms[1]. Anthocyanins are a class of flavonoids ubiquitously distributed in plants. They are types of color-producing compounds in flowers, fruits, seeds, and leaves and provide plants with different colors—from orange-red to blue-purple[2,3]. It is well known that anthocyanins are derived from phenylpropanoids in the flavonoid biosynthesis pathway, in which a series of key enzymes and their encoding genes have been identified[9]. The expression of structural genes (UF3GT, ANS, DFR, F3H, CHI, and CHS) involved in anthocyanin biosynthesis is coordinately mediated by the MBW transcription complex, which is composed of three types of transcription factors (TFs): basic helix-loop-helix (bHLH), R2R3-MYB, and WD40-repeat proteins[10].
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