拟南芥E3泛素连接酶ATL17调控脱落酸抑制主根生长的分子机制研究

E3 ubiquitin ligases play pivotal roles in growth and development in plants. However, it is unclear the mechanisms for ABA inhibition of primary root growth modulated by E3 ubiquitin ligases. Here, we obtained an Arabidopsis mutant that was insensitive to ABA-inhibited primary root elongation by screening a mutant pool. The mutation gene encoded the RING E3 ubiquitin ligase ATL17 (Arabidopsis Tóxicos en Levadura17). Preliminary results indicated that ATL17 had E3 ligase activity. Its actions on ABA inhibition of root growth were closely related to auxin. In this project, we will further identify the substrate protein of ATL17, and investigate the degradation mechanism of the substrate by ATL17. Moreover, the functions and mechanisms for ATL17 regulating auxin distribution and transport, PLETHORAs expression and cell division progression will be uncovered. In addition, we will elucidate the regulatory relationships beween ATL17 and the ABA signaling key components ABI1 (ABA insensitive1), ABI2, ABI4 and ABI5 by analyzing the relevant mutants in ABA-inhibited primary root growth. Together, the molecular mechanisms that ATL17 regulated ABA inhibition of primary root growth through protein ubiquitination in Arabidopsis will be unravelled. A novel mechanism by which a new ABA signal component modulates primary root development may be unveiled in Arabidopsis based on this project.

E3泛素连接酶在植物生长发育中发挥重要作用，但其调控ABA抑制主根生长的机制不清楚。我们筛选到一株拟南芥主根生长对脱落酸（ABA）不敏感的突变体，突变基因编码RING E3泛素连接酶ATL17（Arabidopsis Tóxicos en Levadura17）。初步研究表明，ATL17具有E3泛素连接酶活性，其在ABA抑制主根生长中的作用与生长素相关。本项目拟进一步探明ATL17泛素化的底物蛋白及底物的降解机制，阐明ABA抑制主根发育过程中ATL17对生长素分布和运输、PLETHORAs表达及细胞分裂进程的调控作用。另外，通过分析相关突变体杂交材料明确ABA作用下ATL17与ABI1（ABA insensitive1）、ABI2、ABI4和ABI5的作用关系。最终阐明ATL17介导泛素化修饰调控ABA抑制主根生长的分子机制。本项目有望揭示拟南芥ABA信号中调节主根发育的新成分和新机制。

激素脱落酸（Abscisic acid, ABA）在植物应答多种逆境胁迫反应及调控根生长和种子萌发等过程中发挥重要作用。E3泛素连接酶介导ABA反应，但RING（Really interesting new gene）E3泛素连接酶ATL17（Arabidopsis Tóxicos en Levadura 17）是否在ABA抑制根生长和种子萌发中起作用、具体作用的分子机制如何目前均不清楚。本项目前期发现拟南芥ATL17基因突变体对ABA抑制主根伸长不敏感，在此基础上，我们以多个基因的突变体和过表达植物为材料，利用生化和分子生物学等技术发现ATL17与PP2C蛋白磷酸酶AHG1（ABA hypersensitive germination 1）互作，并证明ATL17通过泛素化降解AHG1正调控ABA抑制根生长和种子萌发；同时发现ATL17通过负调控生长素反应、生长素积累、生长素运输蛋白基因PIN2（PINFORMED2）、PIN4和PIN7表达以及PLT1（PLETHORA 1）的水平在ABA抑制根生长过程中起作用。证明生长素反应因子ARF2（Auxin response factor 2）与ATL17基因启动子结合，可能通过调控ATL17的表达影响ABA介导主根生长。另外发现ATL17通过调节根细胞周期相关基因CYCB2;1（Cyclin B2;1）、KRP2（Kip related protein2）和CYCD3;1的表达在ABA信号中起作用。证明ATL17通过影响ABI5（ABA insensitive 5）或二者协同作用调控ABA反应。这些研究结果揭示了植物E3泛素连接酶ATL17调控ABA反应的新机制。

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