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.

中文翻译：

---

异亮氨酸三联体：对植物防御、根系生长和活性氧形成的独特影响。


异亮氨酸 (ILA) 是一种支链氨基酸相关的 2-羟基羧酸，广泛存在于植物中。增强拟南芥的病原抵抗力并抑制根部生长。水杨酸 (SA) 葡萄糖基转移酶 UGT76B1 能够结合 ILA。在这里，我们研究了 ILA在拟南芥植物中的作用，并揭示了对该小分子的三种不同反应。 ILA 与 SA 协同作用，以 UGT76B1 依赖性方式激活 SA 响应基因表达和抗性，这与观察到的 UGT76B1 对 SA 糖基化的竞争性 ILA 依赖性抑制一致。然而，ILA 也表现出独立于 SA 的应激反应。硝基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 ) 系的超氧化物形成。相反，ILA 对根生长的抑制作用与 SA 和超氧化物诱导无关。 ILA 的这些作用是特异性的，并且不同于其异构化合物亮氨酸和氨基酸异亮氨酸。亮氨酸和异亮氨酸不会诱导防御标记基因的表达或超氧化物的产生，而这两种化合物都会抑制根的生长。在甘蓝型油菜中也观察到了对 ILA 的所有三种反应。