Hirschmanniella oryzae is one of the most devastating nematodes on rice, leading to substantial yield losses. Effector proteins aid the nematode during the infection process by subduing plant defence responses. In this research we characterized two potential H. oryzae effector proteins, chorismate mutase (HoCM) and isochorismatase (HoICM), and investigated their enzymatic activity and their role in plant immunity. Both HoCM and HoICM proved to be enzymatically active in complementation tests in mutant Escherichia coli strains. Infection success by the migratory nematode H. oryzae was significantly higher in transgenic rice lines constitutively expressing HoCM or HoICM. Expression of HoCM, but not HoICM, increased rice susceptibility against the sedentary nematode Meloidogyne graminicola also. Transcriptome and metabolome analyses indicated reductions in secondary metabolites in the transgenic rice plants expressing the potential nematode effectors. The results presented here demonstrate that both HoCM and HoICM suppress the host immune system and that this may be accomplished by lowering secondary metabolite levels in the plant.

中文翻译：

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移殖线虫米氏线虫的两个潜在效应物分支酸突变酶和等轴线酶，通过操纵水稻的次生代谢产物含量来增加宿主易感性

米氏大孢菌是水稻上最具破坏性的线虫之一，导致大量的产量损失。效应蛋白通过抑制植物防御反应，在感染过程中辅助线虫。在这项研究中，我们表征了两种潜在的米曲霉效应子蛋白，分支酸突变酶（HoCM）和异麦芽糖酶（HoICM），并研究了它们的酶促活性及其在植物免疫中的作用。在突变大肠杆菌菌株的互补试验中，HoCM和HoICM均被证明具有酶促活性。在组成型表达HoCM或HoICM的转基因水稻品系中，迁移线虫H. oryzae的感染成功率明显更高。表达HoCM，但不是HoICM，也增加了水稻对久坐的线虫根结线虫的敏感性。转录组和代谢组学分析表明，表达潜在线虫效应子的转基因水稻植株的次生代谢产物减少。此处显示的结果表明，HoCM和HoICM均可抑制宿主免疫系统，这可以通过降低植物中的次生代谢产物水平来实现。