Tang Jinxiang, Yang Dahai, Wu Jianqiang, Chen Suiyun, Wang Lei
Department of Economic Plants and Biotechnology, Yunnan Key Laboratory for Wild Plant Resources, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China.
School of Life Science, Yunnan University, Kunming, 650091, China.
Plant Divers. 2020 Jan 3;42(2):111-119. doi: 10.1016/j.pld.2019.11.005. eCollection 2020 Apr.
Jasmonic acid (JA) plays important roles in plant resistance to insect herbivores. One important derivative of JA is 12-OH-JA, which is produced by two independent pathways: direct hydroxylation of JA by jasmonate-induced oxygenases (JOXs) or hydrolyzation of 12-OH-JA-Ile.Yet the function of 12-OH-JA in plant-herbivore interactions remains largely unknown. In this study, we silenced four JOX homologs independently in the wild tobacco by virus-induced gene silencing (VIGS), and found that all four JOX homologs are involved in JA hydroxylation. Simultaneously silencing the four JA hydroxylases in VIGS-NaJOXs plants decreased herbivory-induced 12-OH-JA by 33%, but JA and JA-Ile levels increased by 45% and 30%, respectively, compared to those in control plants. Compared to direct hydroxylation from JA, hydrolyzation from 12-OH-JA-Ile is equally important for herbivory-induced 12-OH-JA accumulation: in the 12-OH-JA-Ile deficient irJAR4/6 plants, 12-OH-JA decreased 34%. Moreover, VIGS-NaJOXs plants exhibited enhanced resistance to the generalist herbivore . The poor larval performance was strongly correlated with high levels of several JA-Ile-dependent direct defense metabolites in the VIGS-NaJOXs plants. When we simultaneously silenced all four JA hydroxylases in the JA-Ile-deficient irJAR4/6 background, the enhanced herbivore resistance diminished, demonstrating that enhanced herbivore resistance resulted from elevated JA-Ile levels. Given that silencing these genes did not detectably alter plant growth but highly increased plant defense levels, we propose that genes are potential targets for genetic improvement of herbivore-resistant crops.
茉莉酸（JA）在植物对昆虫食草动物的抗性中发挥着重要作用。JA的一种重要衍生物是12-羟基茉莉酸（12-OH-JA），它通过两条独立的途径产生：由茉莉酸诱导的加氧酶（JOXs）直接将JA羟基化，或12-OH-JA-Ile水解。然而，12-OH-JA在植物与食草动物相互作用中的功能仍 largely未知。在本研究中，我们通过病毒诱导基因沉默（VIGS）在野生烟草中独立沉默了四个JOX同源基因，发现所有四个JOX同源基因都参与JA羟基化。与对照植物相比，在VIGS-NaJOXs植物中同时沉默这四个JA羟化酶可使食草动物诱导的12-OH-JA降低33%，但JA和JA-Ile水平分别增加了45%和30%。与JA的直接羟基化相比，12-OH-JA-Ile的水解对于食草动物诱导的12-OH-JA积累同样重要：在12-OH-JA-Ile缺陷的irJAR4/6植物中，12-OH-JA降低了34%。此外，VIGS-NaJOXs植物对多食性食草动物表现出增强的抗性。幼虫生长不良与VIGS-NaJOXs植物中几种依赖JA-Ile的直接防御代谢物的高水平密切相关。当我们在JA-Ile缺陷的irJAR4/6背景中同时沉默所有四个JA羟化酶时，增强的食草动物抗性减弱，表明增强的食草动物抗性是由升高的JA-Ile水平导致的。鉴于沉默这些基因未显著改变植物生长但大幅提高了植物防御水平，我们提出这些基因是抗食草动物作物遗传改良的潜在靶点。
