组蛋白乙酰化介导的生长素信号转导调控顶端分生组织维持的分子机理

Auxin signaling mediates the transcription of down-stream genes by the activity of AUXIN RESPONSE FACTORs (ARFs). ARF family can be divided into two subgroups, including transcriptional activators and repressors. Recent studies revealed the mechanisms of transcriptional regulation mediated by MONOPTEROS (MP/ARF5), one of the transcriptional activators, but those of the repressors remain elusive. Previous studies have shown that MP is involved in the regulation of shoot apical meristem maintenance, while ARF10 and ARF16 regulate the maintenance of root apical meristem. However, whether other ARFs play roles in these processes and how do they exert their functions remain unknown. Our previous work indicates that mutations in ARF3 and its interacting protein ARF3 Interacting Protein 1(AIP1) affected the activity of apical meristems. ARF3 directly binds the promoters of WUS and WOX5 and represses their expression. ARF3 also interacts with SAP18, the subunit of histone deacetylase complex. Defects in ARF3 and AIP1 increased the levels of histione H3 acetylation in WUS and WOX5 promoter regions. Based on these results, we intend to further analyze the regulation of apical meristem maintenance by ARF3—AIP1 interaction, and investigate the molecular mechanisms underlying the transcriptional regulation of ARF3 via mediating histione H3 acetylation. The results will facilitate our understanding on the mechanisms of apical meristem maintenance, and the transcriptional regulation of ARF repressors.

生长素通过其信号转导途径中的ARF家族转录因子调控下游基因转录。ARF家族分为转录激活因子和转录抑制因子两类。近年来的研究工作揭示了转录激活因子MP的作用机制，而以ARF3为代表的转录抑制因子调控下游基因转录的机理目前仍不清楚。研究表明MP参与了茎端分生组织维持，ARF10和ARF16调控根端分生组织维持，然而其他ARF家族成员，尤其是其中的转录抑制因子是否以及如何参与顶端分生组织维持调控尚不清楚。我们的前期工作发现，ARF3及其互作蛋白AIP1突变影响顶端分生组织活动；ARF3直接结合WUS和WOX5启动子并抑制它们转录；ARF3与组蛋白去乙酰化酶复合物的SAP18亚基互作；ARF3和AIP1突变造成WUS和WOX5启动子区域乙酰化水平升高。本申请拟在此基础上进一步研究ARF3—AIP1互作通过调节组蛋白乙酰化修饰调控顶端分生组织维持的机理，为ARF家族转录抑制因子作用机理提供新信息。

位于茎端和根端分生组织的干细胞池作为高等植物发育的新细胞来源，支撑了整个胚后发育过程。生长素在干细胞池维持过程中发挥了重要作用。研究表明，生长素依赖其信号转导系统中的响应因子（AUXIN RESPONSE FACTOR，ARF）调控下游基因转录。ARF家族蛋白可分为转录激活因子和转录抑制因子两类。以ARF5为代表的转录激活因子介导的转录调控机理已有较多研究，但转录抑制因子的作用机理尚不清楚。本项目对转录抑制因子ARF3在干细胞池维持过程中的作用及其调控下游基因转录的机理开展了研究。结果发现，ARF3同时参与了茎端和根端干细胞池的维持过程。研究结果显示，ARF3、ARF3 Interacting Protein1/2（AIP1/2）和Sin3-associated polypeptide of 18 kDa（SAP18）之间存在互作关系，且ARF3、AIP1和SAP18的表达信号在茎端分生组织的周围区域和根端分生组织静止中心上方细胞中重叠。在上述区域中，ARF3直接结合在WOX5和WUS基因的启动子区域，通过与AIP1互作招募SAP18，进而维持合适的组蛋白H3乙酰化水平和正常的WOX5和WUS基因表达模式。高浓度的生长素造成ARF3、AIP1和SAP18之间的互作解离，从而导致组蛋白H3乙酰化水平升高，造成WOX5和WUS基因的异位表达。上述结果表明，ARF3-AIP1/2-SAP18复合物响应生长素浓度，并通过对WOX5和WUS基因表达的精准调控参与了茎端和根端干细胞池的维持。研究结果为理解植物干细胞池的时空调控机制和ARF抑制因子调控下游转录的分子机理提供了新信息。