Regulation of anthocyanin accumulation via MYB75/HAT1/TPL-mediated transcriptional repression

Abstract

Anthocyanin is part of secondary metabolites, which is induced by environmental stimuli and developmental signals, such as high light and sucrose. Anthocyanin accumulation is activated by the MYB-bHLH-WD40 (MBW) protein complex in plants. But the evidence of how plants maintain anthocyanin in response to signals is lacking. Here we perform molecular and genetic evidence to display that HAT1 plays a new breaker of anthocyanin accumulation via post-translational regulations of MBW protein complex. Loss of function of HAT1 in the Arabidopsis seedlings exhibits increased anthocyanin accumulation, whereas overexpression of HAT1 significantly repressed anthocyanin accumulation. We found that HAT1 interacted with MYB75 and thereby interfered with MBW protein complex. Overexpression of HAT1 suppresses abundant anthocyanin phenotype of pap1-D plant. HAT1 is characterized as a transcriptional repressor possessing an N-terminal EAR motif, which determines to interact with TOPLESS corepressor. Repression activity of HAT1 in regulation of gene expression and anthocyanin accumulation can be abolished by deletion or mutation of the EAR motif 1. Chromatin immunoprecipitation assays revealed that MYB75 formed a transcriptional repressor complex with HAT1-TPL by histone H3 deacetylation in target genes. We proposed that HAT1 restrained anthocyanin accumulation by inhibiting the activities of MBW protein complex through blocking the formation of MBW protein complex and recruiting the TPL corepressor to epigenetically modulate the anthocyanin late biosynthetic genes (LBGs).

The MYB–bHLH–WDR interferers (MBWi) epigenetically suppress the MBW's targets

“…Several MBWi have been unravelled such as single‐repeat R3 MYB transcription factors [MYBL2, CAPRICE (CPC), TRIPTYCHON (TRY), ENHANCER OF TRY AND CPC1 (ETC1), ETC2, ETC3, TRICHOMELESS1 (TCL1) and TCL2], JAZ proteins, SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE9 (SPL9) and HD‐ZIP II transcription factor (HAT1) [Perazza et al., ; Schellmann et al., ; Esch et al., ; Kirik et al., , ; Dubos et al., ; Matsui et al., ; Zhu et al., ; Gan et al., ; Gou et al., ; Qi et al., ; Fambrini and Pugliesi, ; Zheng et al., ]. In the absence of MBWi proteins, the MYB, bHLH and WDR can form MBW tertiary transcription factor complexes and activate their targets such as DIHYDROFLAVONOL REDUCTASE ( DFR ) and LEUCOANTHOCYANIDIN OXIDASE ( LDOX ) (involved in anthocyanin biosynthesis) or GLABRA2 ( GL2 ) (involved in epidermal cell fate determination) [Baudry et al., ; Ishida et al., ; Schiefelbein et al., ; Xu et al., ; Fambrini and Pugliesi, ].…”

“…In the absence of JA, JAZ transcription factors can be stabilized and these can form a complex with either TT8 or MYB75 and this also prevents the formation of MBW triple complex [Qi et al., ]. Recently, an HD‐ZIP II transcription factor, HAT1, has been identified to function as a negative regulator of anthocyanin biosynthesis [Zheng et al., ]. Similarly to MYBL2 , HAT1 gene was also found to strongly express under low‐intensity light conditions [Zheng et al., ].…”

“…Recently, an HD‐ZIP II transcription factor, HAT1, has been identified to function as a negative regulator of anthocyanin biosynthesis [Zheng et al., ]. Similarly to MYBL2 , HAT1 gene was also found to strongly express under low‐intensity light conditions [Zheng et al., ]. Besides, drought stress was found to increase the phosphorylation of HAT1 which may result in degradation of this protein [Tan et al., ].…”

“…Besides, drought stress was found to increase the phosphorylation of HAT1 which may result in degradation of this protein [Tan et al., ]. Under favourable conditions, the accumulated or stabilized HAT1 proteins can sequester the MBW protein complex via its interaction with MYB75 protein [Zheng et al., ]. Interestingly, MYBL2, HAT1 and several JAZ proteins (JAZ5, 6, 7 and 8) were evidenced to have an EAR motif or EAR‐like motif which mediates the transcriptional repression in plants [Matsui et al., ; Kagale et al., ; Zheng et al., ] (Table ).…”

“…Under favourable conditions, the accumulated or stabilized HAT1 proteins can sequester the MBW protein complex via its interaction with MYB75 protein [Zheng et al., ]. Interestingly, MYBL2, HAT1 and several JAZ proteins (JAZ5, 6, 7 and 8) were evidenced to have an EAR motif or EAR‐like motif which mediates the transcriptional repression in plants [Matsui et al., ; Kagale et al., ; Zheng et al., ] (Table ). Since the owning of the transcriptional repression motif, MYBL2, HAT1 and some JAZ proteins were also found to recruit TPL or TPL‐related (TPR) corepressors to suppress their targets [Causier et al., ; Zheng et al., ] (Table ).…”