Singh Richard Raj, Verstraeten Bruno, Siddique Shahid, Tegene Adelahu Mekonene, Tenhaken Raimund, Frei Michael, Haeck Ashley, Demeestere Kristof, Pokhare Somnath, Gheysen Godelieve, Kyndt Tina
Department of Biotechnology, Ghent University, Ghent, Belgium.
Institute of Crop Science and Resource Conservation, Department of Molecular Phytomedicine, University of Bonn, Bonn, Germany.
J Exp Bot. 2020 Jul 6;71(14):4271-4284. doi: 10.1093/jxb/eraa171.
Ascorbic acid (AA) is the major antioxidant buffer produced in the shoot tissue of plants. Previous studies on root-knot nematode (RKN; Meloidogyne graminicola)-infected rice (Oryza sativa) plants showed differential expression of AA-recycling genes, although their functional role was unknown. Our results confirmed increased dehydroascorbate (DHA) levels in nematode-induced root galls, while AA mutants were significantly more susceptible to nematode infection. External applications of ascorbate oxidase (AO), DHA, or reduced AA, revealed systemic effects of ascorbate oxidation on rice defence versus RKN, associated with a primed accumulation of H2O2 upon nematode infection. To confirm and further investigate these systemic effects, a transcriptome analysis was done on roots of foliar AO-treated plants, revealing activation of the ethylene (ET) response and jasmonic acid (JA) biosynthesis pathways in roots, which was confirmed by hormone measurements. Activation of these pathways by methyl-JA, or ethephon treatment can complement the susceptibility phenotype of the rice Vitamin C (vtc1) mutant. Experiments on the jasmonate signalling (jar1) mutant or using chemical JA/ET inhibitors confirm that the effects of ascorbate oxidation are dependent on both the JA and ET pathways. Collectively, our data reveal a novel pathway in which ascorbate oxidation induces systemic defence against RKNs.
抗坏血酸（AA）是植物地上组织中产生的主要抗氧化缓冲物质。先前对感染根结线虫（RKN；禾谷根结线虫）的水稻（Oryza sativa）植株的研究表明，AA循环基因存在差异表达，但其功能作用尚不清楚。我们的结果证实，线虫诱导的根瘿中脱氢抗坏血酸（DHA）水平升高，而AA突变体对线虫感染的敏感性明显更高。抗坏血酸氧化酶（AO）、DHA或还原型AA的外源应用揭示了抗坏血酸氧化对水稻抗RKN防御的系统影响，这与线虫感染时H2O2的引发积累有关。为了证实并进一步研究这些系统影响，对经叶面AO处理的植株的根进行了转录组分析，结果显示根中乙烯（ET）反应和茉莉酸（JA）生物合成途径被激活，激素测量结果证实了这一点。用茉莉酸甲酯或乙烯利处理激活这些途径可以弥补水稻维生素C（vtc1）突变体的敏感表型。对茉莉酸信号转导（jar1）突变体进行的实验或使用化学JA/ET抑制剂的实验证实，抗坏血酸氧化的影响依赖于JA和ET途径。总的来说，我们的数据揭示了一条新的途径，即抗坏血酸氧化诱导对根结线虫的系统防御。
