ESR2–HDA6 complex negatively regulates auxin biosynthesis to delay callus initiation in Arabidopsis leaf explants during tissue culture

Plants exhibit an astonishing ability to regulate organ regeneration upon wounding.Excision of leaf explants promotes the biosynthesis of indole-3-acetic acid(IAA),which is polar-transported to excised regions,where cell fate transition leads to root founder cell specification to induce de novo root regeneration.The regeneration capacity of plants has been utilized to develop in vitro tissue culture technologies.Here,we report that IAA accumulation near the wounded site of leaf explants is essential for callus formation on 2,4-dichlorophenoxyacetic acid(2,4-D)-rich callus-inducing medium(CIM).Notably,a high concentration of 2,4-D does not compensate for the action of IAA because of its limited efflux;rather,it lowers IAA biosynthesis via a negative feedback mechanism at an early stage of in vitro tissue culture,delaying callus initiation.The auxin negative feedback loop in CIM-cultured leaf explants is mediated by an auxin-inducible APETALA2 transcription factor,ENHANCER OF SHOOT REGENERATION 2(ESR2),along with its interacting partner HISTONE DEACETYLASE 6(HDA6).The ESR2–HDA6 complex binds directly to,and removes the H3ac mark from,the YUCCA1(YUC1),YUC7,and YUC9 loci,consequently repressing auxin biosynthesis and inhibiting cell fate transition on 2,4-D-rich CIM.These findings indicate that negative feedback regulation of auxin biosynthesis by ESR2 and HDA6 interferes with proper cell fate transition and callus initiation.

A domesticated Harbinger transposase forms a complex with HDA6 and promotes histone H3 deacetylation at genes but not TEs in Arabidopsis

In eukaryotes,histone acetylation is a major modification on histone N-terminal tails that is tightly connected to transcriptional activation.HDA6 is a histone deacetylase involved in the transcriptional regulation of genes and transposable elements(TEs)in Arabidopsis thaliana.HDA6 has been shown to participate in several complexes in plants,including a conserved SIN3 complex.Here,we uncover a novel protein complex containing HDA6,several Harbinger transposon-derived proteins(HHP1,SANT1,SANT2,SANT3,and SANT4),and MBD domain-containing proteins(MBD1,MBD2,and MBD4).We show that mutations of all four SANT genes in the sant-null mutant cause increased expression of the flowering repressors FLC,MAF4,and MAF5,resulting in a late flowering phenotype.Transcriptome deep sequencing reveals that while the SANT proteins and HDA6 regulate the expression of largely overlapping sets of genes,TE silencing is unaffected in sant-null mutants.Our global histone H3 acetylation profiling shows that SANT proteins and HDA6 modulate gene expression through deacetylation.Collectively,our findings suggest that Harbinger transposon-derived SANT domain-containing proteins are required for histone deacetylation and flowering time control in plants.

AhHDA1异源表达影响拟南芥植株干旱性

将花生组蛋白去乙酰化酶1基因(Arachis hygogaea histone deacetylase 1,AhHDA1)转化拟南芥野生型Col-0和突变体had6,对获得的纯合转基因植株进行抗旱性分析,并对ABA合成及相关响应基因表达进行检测.结果表明:AhHDA1蛋白定位于细胞核,在干旱条件下,与hda6突变体比较,p35S%HDA1/hda6拟南芥植株的叶片相对含水量降低,气孔开度增大,干旱存活率降低,基本回复了Col的表型;体内ABA合成关键酶基因At NCED3和ABA信号途径重要转录因子At ABF3基因的表达降低,但RD29A基因表达提高.而p35S%HDA1/Col较p35S%HDA1/hda6和Col的抗旱性关键生理指标降低更加显著.说明hda6突变体表型回复确实由于外源AhHDA1的表达引起的,推测AhHDA1影响植物抗旱性与ABA的合成与信号通路相关.

蒺藜苜蓿MtFVE基因功能初步解析

拟南芥(Arabidopsis thaliana)中自主通路成员FLOWERING LOCUS VE(FVE)主要通过表观遗传学机制抑制其下游开花抑制子FLOWERING LOCUS C(FLC)的表达从而促进开花,但有研究发现蒺藜苜蓿(Medicago truncatula)中没有FLC的同源基因,因此,蒺藜苜蓿中FVE同源基因调控开花时间的分子作用机理还有待研究。通过生物信息学方法在蒺藜苜蓿中筛选到2个拟南芥FVE的同源蛋白,将其分别命名为MtFVEa和MtFVEb。经氨基酸序列比对发现,2个蛋白均具有典型的WD40蛋白结合结构域。随后通过qRT-PCR和半定量RT-PCR检测MtFVEa和MtFVEb基因组织表达特异性,发现2个基因在花和营养生长期的茎尖具有较高水平的表达。经酵母双杂实验进一步分析发现,MtFVEa蛋白与MtFLD [拟南芥FLOWERING LOCUS D(FLD)的同源蛋白]和MtHDA6 [拟南芥histone deacetylase 6(HDA6)的同源蛋白]均发生蛋白互作,表明MtFVE可能同样形成FVE-FLD-HDA6三元复合体参与蒺藜苜蓿开花调控。研究结果为进一步探索蒺藜苜蓿MtFVE基因的功能提供了研究思路和理论支持。

Regulation of jasmonate signaling by reversible acetylation of TOPLESS in Arabidopsis

The plant hormone jasmonate(JA)regulates plant immunity and adaptive growth by orchestrating a genome-wide transcriptional program.Key regulators of JA-responsive gene expression include the master transcription factor MYc2,which is repressed by the conserved Groucho/Tup1-like corepressor TOPLESS(TPL)in the resting state.However,the mechanisms underlying TPL-mediated transcriptional repression of MYc2 activity and hormone-dependent switching between repression and de-repression remainenigmatic.Here,we report the regulation of TPLactivity and JAsignaling byreversibleacetylation of TPL.We found that the histone acetyltransferase GCN5 could mediate TPL acetylation,which enhances its interaction with the NOVEL-INTERACTOR-OF-JAZ(NINJA)adaptor and promotes its recruitment to MYc2 target promoters,facilitating transcriptional repression.Conversely,TPL deacetylation by the histonedeacetylase HDA6 weakens TPL-NINJA interaction and inhibitsTPL recruitmentto MYC2 target promoters,facilitating transcriptional activation.In the resting state,the opposing activities of GCN5 and HDA6 maintain TPL acetylation homeostasis,promoting transcriptional repression activity of TPL.In response to JA elicitation,HDA6 expression is transiently induced,resulted in decreased TPL acetylation and repressor activity,thereby transcriptional activation of MYC2 target genes.Thus,the GCN5-TPL-HDA6 module main tains the homeostasis of acetylated TPL,thereby determining the transcriptional state of JA-responsive genes.Our findings uncovered a mechanism by which the TPL corepressor activity in JA signaling is activelytuned inarapidandreversiblemanner.

Arabidopsis RPD3-like histone deacetylases form multiple complexes involved in stress response

The Arabidopsis thaliana RPD3-type histone deacetylases have been known to form conserved SIN3-type histone deacetylase complexes,but whether they form other types of complexes is unknown.Here,we perform affinity purification followed by mass spectrometry and demonstrate that the Arabidopsis RPD3-type histone deacetylases HDA6 and HDA19 interact with several previously uncharacterized proteins,thereby forming three types of plant-specific histone deacetylase complexes,which we named SANT,ESANT,and ARID.RNA-seq indicates that the newly identified components function together with HDA6 and HDA19 and coregulate the expression of a number of genes.HDA6 and HDA19 were previously thought to repress gene transcription by histone deacetylation.We find that the histone deacetylase complexes can repress gene expression via both histone deacetylation-dependent and-independent mechanisms.In the mutants of histone deacetylase complexes,the expression of a number of stressinduced genes is up-regulated,and several mutants of the histone deacetylase complexes show severe retardation in growth.Considering that growth retardation is thought to be a trade-off for an increase in stress tolerance,we infer that the histone deacetylase complexes identified in this study prevent overexpression of stress-induced genes and thereby ensure normal growth of plants under nonstress conditions.