Departamento de Genética Molecular y Microbiología, Pontificia Universidad Católica de Chile, Santiago 8331010, Chile.
Proc Natl Acad Sci U S A. 2010 Mar 2;107(9):4477-82. doi: 10.1073/pnas.0909571107. Epub 2010 Feb 8.
One of the most striking examples of plant developmental plasticity to changing environmental conditions is the modulation of root system architecture (RSA) in response to nitrate supply. Despite the fundamental and applied significance of understanding this process, the molecular mechanisms behind nitrate-regulated changes in developmental programs are still largely unknown. Small RNAs (sRNAs) have emerged as master regulators of gene expression in plants and other organisms. To evaluate the role of sRNAs in the nitrate response, we sequenced sRNAs from control and nitrate-treated Arabidopsis seedlings using the 454 sequencing technology. miR393 was induced by nitrate in these experiments. miR393 targets transcripts that code for a basic helix-loop-helix (bHLH) transcription factor and for the auxin receptors TIR1, AFB1, AFB2, and AFB3. However, only AFB3 was regulated by nitrate in roots under our experimental conditions. Analysis of the expression of this miR393/AFB3 module, revealed an incoherent feed-forward mechanism that is induced by nitrate and repressed by N metabolites generated by nitrate reduction and assimilation. To understand the functional role of this N-regulatory module for plant development, we analyzed the RSA response to nitrate in AFB3 insertional mutant plants and in miR393 overexpressors. RSA analysis in these plants revealed that both primary and lateral root growth responses to nitrate were altered. Interestingly, regulation of RSA by nitrate was specifically mediated by AFB3, indicating that miR393/AFB3 is a unique N-responsive module that controls root system architecture in response to external and internal N availability in Arabidopsis.
植物对环境变化的发育可塑性的一个最显著的例子是根系结构 (RSA) 对硝酸盐供应的响应的调节。尽管了解这一过程具有根本和应用意义，但硝酸盐调节发育程序变化背后的分子机制在很大程度上仍然未知。小 RNA (sRNA) 已成为植物和其他生物体中基因表达的主要调控因子。为了评估 sRNA 在硝酸盐响应中的作用，我们使用 454 测序技术对对照和硝酸盐处理的拟南芥幼苗中的 sRNA 进行了测序。在这些实验中，miR393 被硝酸盐诱导。miR393 的靶标转录本编码一个基本螺旋-环-螺旋 (bHLH) 转录因子和生长素受体 TIR1、AFB1、AFB2 和 AFB3。然而，只有 AFB3 在我们的实验条件下受硝酸盐调节。对该 miR393/AFB3 模块的表达分析表明，存在一个由硝酸盐诱导并被硝酸盐还原和同化产生的 N 代谢物抑制的非相干前馈机制。为了了解该 N 调节模块对植物发育的功能作用，我们分析了 AFB3 插入突变体植物和 miR393 过表达植物对硝酸盐的 RSA 响应。这些植物的 RSA 分析表明，硝酸盐对主根和侧根生长的响应都发生了改变。有趣的是，硝酸盐对 RSA 的调节是由 AFB3 特异性介导的，这表明 miR393/AFB3 是一个独特的 N 响应模块，它控制拟南芥对外源和内源 N 可用性的根系结构。
