The iron deficiency response in Arabidopsis thaliana requires the phosphorylated transcription factor URI
The iron deficiency response in Arabidopsis thaliana requires the phosphorylated transcription factor URI
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DOI：
10.1073/pnas.1916892116
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发表时间：
2019-12-10
影响因子：
11.1
通讯作者：
Guerinot, Mary Lou
中科院分区：
文献类型：
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作者：
Kim, Sun A.;LaCroix, Ian S.;Guerinot, Mary Lou
铁是植物必需的营养物质，但过量的铁是有毒的，因为它在羟基自由基的形成中起催化作用。因此，只有在缺铁的情况下，铁的摄取才会受到高度调节和诱导。根系吸收铁的机制已经很好地描述了，但对植物如何感知缺铁知之甚少。我们发现一个碱性螺旋-环-螺旋（bHLH）转录因子IRT1上游调控因子（URI）是拟南芥缺铁信号通路的重要组成部分。uri突变体在诱导铁调节转运蛋白1 （IRT1）和铁还原氧化酶2 （FRO2）及其转录调控因子fe -like铁缺乏诱导转录因子（FIT）和bHLH38/ 39/100/101响应铁缺乏方面存在缺陷。染色质免疫沉淀测序（ChIP-seq）显示URI与许多铁调控基因的启动子直接结合，包括bHLH38/39/100/101，但不包括FIT。尽管URI转录物和蛋白的表达与铁的状态无关，但URI的磷酸化形式仅在缺铁的情况下积累。在铁补给过程中，磷酸化URI受到蛋白酶体依赖性降解的影响，磷酸化URI的周转依赖于E3连接酶BTS。IVc bHLH转录因子亚群，先前已被证明调节bHLH38/39/100/101，主要在缺铁条件下与URI共免疫沉淀，这表明URI是能够在体内形成异源二聚体的磷酸化形式。我们认为URI的磷酸化形式在缺铁条件下积累，与IVc亚群蛋白形成异源二聚体，并诱导bHLH38/39/100/101的转录。这些转录因子反过来与FIT异二聚化，并驱动IRT1和FRO2的转录以增加铁的摄取。
Iron is an essential nutrient for plants, but excess iron is toxic due to its catalytic role in the formation of hydroxyl radicals. Thus, iron uptake is highly regulated and induced only under iron deficiency. The mechanisms of iron uptake in roots are well characterized, but less is known about how plants perceive iron deficiency. We show that a basic helix-loop-helix (bHLH) transcription factor Upstream Regulator of IRT1 (URI) acts as an essential part of the iron deficiency signaling pathway in Arabidopsis thaliana. The uri mutant is defective in inducing Iron-Regulated Transporter1 (IRT1) and Ferric Reduction Oxidase2 (FRO2) and their transcriptional regulators FER-like iron deficiency-induced transcription factor (FIT) and bHLH38/ 39/100/101 in response to iron deficiency. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) reveals direct binding of URI to promoters of many iron-regulated genes, including bHLH38/39/100/101 but not FIT. While URI transcript and protein are expressed regardless of iron status, a phosphorylated form of URI only accumulates under iron deficiency. Phosphorylated URI is subject to proteasome-dependent degradation during iron resupply, and turnover of phosphorylated URI is dependent on the E3 ligase BTS. The subgroup IVc bHLH transcription factors, which have previously been shown to regulate bHLH38/39/100/101, coimmunoprecipitate with URI mainly under Fe-deficient conditions, suggesting that it is the phosphorylated form of URI that is capable of forming heterodimers in vivo. We propose that the phosphorylated form of URI accumulates under Fe deficiency, forms heterodimers with subgroup IVc proteins, and induces transcription of bHLH38/39/100/101. These transcription factors in turn heterodimerize with FIT and drive the transcription of IRT1 and FRO2 to increase Fe uptake.