Bauer Sibylle, Mekonnen Dereje W, Geist Birgit, Lange Birgit, Ghirardo Andrea, Zhang Wei, Schäffner Anton R
Institute of Biochemical Plant Pathology, Department of Environmental Sciences, Helmholtz Zentrum München, München, Germany.
Institute of Biochemical Plant Pathology, Environmental Simulation Unit, Department of Environmental Sciences, Helmholtz Zentrum München, München, Germany.
J Exp Bot. 2020 Jul 6;71(14):4258-4270. doi: 10.1093/jxb/eraa160.
Isoleucic acid (ILA), a branched-chain amino acid-related 2-hydroxycarboxylic acid, occurs ubiquitously in plants. It enhances pathogen resistance and inhibits root growth of Arabidopsis. The salicylic acid (SA) glucosyltransferase UGT76B1 is able to conjugate ILA. Here, we investigate the role of ILA in planta in Arabidopsis and reveal a triad of distinct responses to this small molecule. ILA synergistically co-operates with SA to activate SA-responsive gene expression and resistance in a UGT76B1-dependent manner in agreement with the observed competitive ILA-dependent repression of SA glucosylation by UGT76B1. However, ILA also shows an SA-independent stress response. Nitroblue tetrazolium staining and pharmacological experiments indicate that ILA induces superoxide formation of the wild type and of an SA-deficient (NahG sid2) line. In contrast, the inhibitory effect of ILA on root growth is independent of both SA and superoxide induction. These effects of ILA are specific and distinct from its isomeric compound leucic acid and from the amino acid isoleucine. Leucic acid and isoleucine do not induce expression of defense marker genes or superoxide production, whereas both compounds inhibit root growth. All three responses to ILA are also observed in Brassica napus.
异亮氨酸（ILA）是一种与支链氨基酸相关的2-羟基羧酸，广泛存在于植物中。它能增强植物对病原体的抗性并抑制拟南芥的根生长。水杨酸（SA）糖基转移酶UGT76B1能够使ILA糖基化。在此，我们研究了ILA在拟南芥植株中的作用，并揭示了对这种小分子的三种不同反应。ILA与SA协同作用，以UGT76B1依赖的方式激活SA响应基因的表达和抗性，这与观察到的UGT76B1对SA糖基化的ILA依赖竞争性抑制一致。然而，ILA也表现出不依赖SA的应激反应。氮蓝四唑染色和药理学实验表明，ILA诱导野生型和SA缺陷型（NahG sid2）品系的超氧化物形成。相比之下，ILA对根生长的抑制作用与SA和超氧化物诱导均无关。ILA的这些作用具有特异性，不同于其同分异构体亮氨酸和氨基酸异亮氨酸。亮氨酸和异亮氨酸不诱导防御标记基因的表达或超氧化物产生，而这两种化合物均抑制根生长。在甘蓝型油菜中也观察到了对ILA的这三种反应。
