Wang Wujian, Ye Jun, Xu Heng, Liu Xi, Fu Yue, Zhang Hui, Rouached Hatem, Whelan James, Shen Zhenguo, Zheng Luqing
College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, 210095, China.
Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA.
New Phytol. 2022 Jun;234(5):1753-1769. doi: 10.1111/nph.18096. Epub 2022 Apr 2.
As excess iron (Fe) is toxic, uptake of this essential micronutrient must be tightly controlled. Previous studies have shown that Oryza sativa (rice) POSITIVE REGULATOR OF IRON HOMEOSTASIS1 (OsPRI1) acts upstream of the iron-related transcription factor 2 (OsIRO2) and OsIRO3 to positively regulate root-to-shoot Fe translocation. However, as expression of OsPRI1 is constitutive it is unclear how the Fe-deficiency response is turned off to prevent toxicity when Fe is sufficient. The bHLH transcription factor OsbHLH061 interacts with OsPRI1, and this study used molecular, genetics, biochemical and physiological approaches to functionally characterise OsbHLH061 and how it affects Fe homeostasis. OsbHLH061 knockout or overexpression lines increase or decrease Fe accumulation in shoots respectively. Mechanistically, OsbHLH061 expression is upregulated by high Fe, and physically interacts with OsPRI1, the OsbHLH061-OsPRI1 complex recruits TOPLESS/TOPLESS-RELATED (OsTPL/TPR) co-repressors to repress OsIRO2 and OsIRO3 expression. The OsbHLH061 ethylene-responsive element-binding factor-associated amphiphilic repression (EAR) motif is required for this transcriptional repression activity. These results define a functional OsTPL/TPR-OsbHLH061-OsPRI1-OsIRO2/3 module that negatively controls long-distance transport of Fe in plants for adaptation to changing Fe environments and maintain Fe homeostasis in rice.
由于过量的铁（Fe）具有毒性，必须严格控制这种必需微量营养素的摄取。先前的研究表明，水稻铁稳态正向调节因子1（OsPRI1）在铁相关转录因子2（OsIRO2）和OsIRO3的上游起作用，以正向调节从根到地上部的铁转运。然而，由于OsPRI1的表达是组成型的，目前尚不清楚在铁充足时，缺铁反应是如何关闭以防止毒性的。bHLH转录因子OsbHLH061与OsPRI1相互作用，本研究使用分子、遗传、生化和生理学方法对OsbHLH061及其影响铁稳态的方式进行功能表征。OsbHLH061基因敲除或过表达系分别增加或减少地上部的铁积累。从机制上讲，高铁会上调OsbHLH061的表达，并且它与OsPRI1发生物理相互作用，OsbHLH061-OsPRI1复合物募集无顶/无顶相关（OsTPL/TPR）共抑制因子来抑制OsIRO2和OsIRO3的表达。这种转录抑制活性需要OsbHLH061的乙烯反应元件结合因子相关两亲性抑制（EAR）基序。这些结果确定了一个功能性的OsTPL/TPR-OsbHLH061-OsPRI1-OsIRO2/3模块，该模块负向控制植物中铁的长距离运输，以适应不断变化的铁环境并维持水稻中的铁稳态。
