拟南芥转录因子MYBa/b与bZIPx/y协同调控铅积累和耐受的分子机制

Our previous studies revealed that Arabidopsis transcription factors MYBa/b and bZIPx/y are involved in regulating lead (Pb) accumulation and tolerance. Our preliminary studies showed that loss-of-function of MYBa/b genes led to reduced Pb accumulation and enhanced Pb tolerance, whereas loss-of-function of bZIPx/y genes led to enhanced Pb accumulation and reduced Pb tolerance. Further studies using yeast-one-hybrid and yeast-two-hybrid showed that transcript factors MYBa and bZIPx could directly bind to upstream regions of AtPDR12 promoter, and MYBa/b interacted with bZIPx/y. We postulated that MYBa/b might interact with bZIPx/y to coordinately regulate Pb tolerance by modulating AtPDR12 expression in Arabidopsis. In this work, we will further study the functions of MYBa/b and bZIPx/y in regulating Pb tolerance and Pb accumulation, confirm the protein interactions between MYBa/b and bZIPx/y as well as their effects on expression of the downstream gene AtPDR12, and uncover the molecular mechanisms mediated by MYBa/b and bZIPx/y in response to Pb stress. These results will provide not only new insights into understanding the mechanisms involved in tolerance of plants to Pb stress but also the novel candidate genes for engineering efficient plants for phytoremediation of heavy metal-contaminated soils.

在前期研究中我们发现拟南芥转录因子MYBa/b与bZIPx/y参与调控重金属铅（Pb）胁迫耐受。初步研究表明，MYBa/b基因功能缺失导致植株的Pb含量降低及Pb胁迫耐受，而bZIPx/y基因功能缺失导致植株的Pb含量升高及Pb胁迫敏感；此外，酵母单杂交分析显示，MYBa和bZIPx与Pb离子泵AtPDR12启动子上游区段直接结合；酵母双杂交分析显示，MYBa与MYBb、bZIPx与bZIPy、MYBa与bZIPx存在蛋白互作。据此推测：MYBa/b与bZIPx/y可能通过蛋白互作来协同调节AtPDR12转录，进而控制植株的Pb积累及耐受。本项目拟在此基础上进一步研究MYBa/b与bZIPx/y互作及其对下游靶基因AtPDR12的调控作用，阐明其协同调控Pb胁迫响应的分子机理。该研究不仅有助于揭示植物调控重金属积累和耐受的机理，而且可为利用植物修复技术治理土壤重金属污染提供新的基因资源。

重金属污染是非常严重的环境问题，对人类的生存环境与、食品安全及健康产生极大威胁。本研究对MYBa、MYBb、bZIPx、bZIPy在植物应对重金属铅胁迫的作用机理进行了深入研究，首次证实MYBa与MYBb在铅胁迫应答中起负调控作用，bZIPx与bZIPy在铅胁迫应答中起正调控作用。MYBa-MYBb、MYBa-bZIPx、bZIPx-bZIPy间存在蛋白-蛋白相互作用，其关键的相互作用区域位于中端的亮氨酸拉链结构域。此外，酵母单杂交、ChIP-qPCR、报告基因表达系统分析等实验从多个角度证实，MYBa、MYBb、bZIPx、bZIPy均通过铅离子泵PDR12进行重要的调控作用，其中MYBa与bZIPx直接结合到PDR12上游启动子区域的不同区段。进一步的遗传分析结果表明，MYBa/MYBb与bZIPx/bZIPy对PDR12的调控为负相关，推测四者间结合到DNA顺式元件后可通过蛋白-蛋白相互作用进行动态调节，实现PDR12表达水平调控，从而适应环境中不同的生长条件。本研究为了解植物调控重金属铅胁迫应答机理提供了重要的理论基础，并可为环境重金属污染治理、作物遗传改良降低其中重金属含量提供理论参考。.