Brenner E D, Martinez-Barboza N, Clark A P, Liang Q S, Stevenson D W, Coruzzi G M
Department of Biology, New York University, New York, New York 10003, USA.
Plant Physiol. 2000 Dec;124(4):1615-24. doi: 10.1104/pp.124.4.1615.
Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channels that are the predominant neuroreceptors in the mammalian brain. Genes with high sequence similarity to animal iGluRs have been identified in Arabidopsis. To understand the role of Arabidopsis glutamate receptor-like (AtGLR) genes in plants, we have taken a pharmacological approach by examining the effects of BMAA [S(+)-beta-methyl-alpha, beta-diaminopropionic acid], a cycad-derived iGluR agonist, on Arabidopsis morphogenesis. When applied to Arabidopsis seedlings, BMAA caused a 2- to 3-fold increase in hypocotyl elongation and inhibited cotyledon opening during early seedling development. The effect of BMAA on hypocotyl elongation is light specific. Furthermore, BMAA effects on early morphogenesis of Arabidopsis can be reversed by the simultaneous application of glutamate, the native iGluR agonist in animals. To determine the targets of BMAA action in Arabidopsis, a genetic screen was devised to isolate Arabidopsis mutants with a BMAA insensitive morphology (bim). When grown in the light on BMAA, bim mutants exhibited short hypocotyls compared with wild type. bim mutants were grouped into three classes based on their morphology when grown in the dark in the absence of BMAA. Class-I bim mutants have a normal, etiolated morphology, similar to wild-type plants. Class-II bim mutants have shorter hypocotyls and closed cotyledons when grown in the dark. Class-III bim mutants have short hypocotyls and open cotyledons when grown in the dark, resembling the previously characterized constitutively photomorphogenic mutants (cop, det, fus, and shy). Further analysis of the bim mutants should help define whether plant-derived iGluR agonists target glutamate receptor signaling pathways in plants.
离子型谷氨酸受体（iGluRs）是配体门控离子通道，是哺乳动物大脑中主要的神经受体。在拟南芥中已鉴定出与动物iGluRs具有高度序列相似性的基因。为了了解拟南芥谷氨酸受体样（AtGLR）基因在植物中的作用，我们采用了药理学方法，通过研究苏铁衍生的iGluR激动剂BMAA [S(+)-β-甲基-α,β-二氨基丙酸]对拟南芥形态发生的影响。当将BMAA应用于拟南芥幼苗时，在幼苗早期发育过程中，它会导致下胚轴伸长增加2至3倍，并抑制子叶张开。BMAA对下胚轴伸长的影响具有光特异性。此外，通过同时应用动物体内天然的iGluR激动剂谷氨酸，可以逆转BMAA对拟南芥早期形态发生的影响。为了确定BMAA在拟南芥中的作用靶点，设计了一个遗传筛选来分离具有BMAA不敏感形态（bim）的拟南芥突变体。当在光照下于BMAA上生长时，与野生型相比，bim突变体表现出短的下胚轴。根据在无BMAA的黑暗条件下生长时的形态，bim突变体被分为三类。I类bim突变体具有正常的黄化形态，类似于野生型植物。II类bim突变体在黑暗中生长时具有较短的下胚轴和闭合的子叶。III类bim突变体在黑暗中生长时具有短的下胚轴和张开的子叶，类似于先前鉴定的组成型光形态建成突变体（cop、det、fus和shy）。对bim突变体的进一步分析应有助于确定植物衍生的iGluR激动剂是否靶向植物中的谷氨酸受体信号通路。
