Centre for Sustainable Agriculture, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
J Exp Bot. 2014 Mar;65(3):779-87. doi: 10.1093/jxb/ert335. Epub 2013 Oct 22.
As a signalling molecule, glutamate is best known for its role as a fast excitatory neurotransmitter in the mammalian nervous system, a role that requires the activity of a family of ionotropic glutamate receptors (iGluRs). The unexpected discovery in 1998 that Arabidopsis thaliana L. possesses a family of iGluR-related (GLR) genes laid the foundations for an assessment of glutamate's potential role as a signalling molecule in plants that is still in progress. Recent advances in elucidating the function of Arabidopsis GLR receptors has revealed similarities with iGluRs in their channel properties, but marked differences in their ligand specificities. The ability of plant GLR receptors to act as amino-acid-gated Ca(2+) channels with a broad agonist profile, combined with their expression throughout the plant, makes them strong candidates for a multiplicity of amino acid signalling roles. Although root growth is inhibited in the presence of a number of amino acids, only glutamate elicits a specific sequence of changes in growth, root tip morphology, and root branching. The recent finding that the MEKK1 gene is a positive regulator of glutamate sensitivity at the root tip has provided genetic evidence for the existence in plants of a glutamate signalling pathway analogous to those found in animals. This short review will discuss the most recent advances in understanding glutamate signalling in roots, considering them in the context of previous work in plants and animals.
作为一种信号分子，谷氨酸以其在哺乳动物神经系统中作为快速兴奋性神经递质的作用而闻名，这一作用需要一系列离子型谷氨酸受体（iGluRs）的活性。1998 年出人意料的发现，拟南芥（Arabidopsis thaliana L.）拥有一系列与 iGluR 相关的（GLR）基因，为评估谷氨酸作为植物中信号分子的潜在作用奠定了基础，而这一作用仍在进行中。最近在阐明拟南芥 GLR 受体功能方面的进展揭示了它们在通道特性上与 iGluRs 的相似性，但在配体特异性上存在显著差异。植物 GLR 受体能够作为具有广泛激动剂谱的氨基酸门控 Ca(2+)通道发挥作用，加上它们在整个植物中的表达，使它们成为多种氨基酸信号作用的强有力候选者。尽管存在许多氨基酸会抑制根的生长，但只有谷氨酸会引起生长、根尖形态和根分枝的特定变化序列。最近发现，MEKK1 基因是根尖谷氨酸敏感性的正调节剂，为植物中存在类似于动物中发现的谷氨酸信号通路提供了遗传证据。这篇简短的综述将讨论在理解根中谷氨酸信号方面的最新进展，同时考虑到之前在植物和动物中的研究工作。
