Long Qin, Xie Yu, He Yongrui, Li Qiang, Zou Xiuping, Chen Shanchun
Citrus Research Institute, Southwest University/Chinese Academy of Agricultural Sciences, Chongqing, China.
Front Plant Sci. 2019 Dec 20;10:1634. doi: 10.3389/fpls.2019.01634. eCollection 2019.
Antagonism between jasmonic acid (JA) and salicylic acid (SA) plays pivotal roles in the fine-tuning of plant immunity against pathogen infection. In this study, we compared the phytohormonal responses to subsp. (Xcc) between the citrus canker-susceptible (S) cultivar Wanjincheng orange ( Osbeck) and -resistant (R) cultivar Jindan ( Swingle). Upon Xcc infection, SA and JA were strongly induced in Jindan (R) and Wanjincheng orange (S), respectively, and JA appeared to contribute to citrus disease susceptibility by antagonizing SA-mediated effective defenses. A homologous gene encoding the allene oxide synthase (AOS) 1-2 enzyme, which catalyzes the first committed step in JA biosynthesis, was specifically upregulated in Wanjincheng orange (S) but not in Jindan (R). A promoter sequence analysis showed that abscisic acid (ABA)-responsive elements are enriched in the of Wanjincheng orange (S) but not in Jindan (R). Accordingly, ABA treatments could induce expression and JA accumulation, leading to enhanced citrus disease susceptibility in Wanjincheng orange (S), while the synthesis inhibitor sodium tungstate had the opposite effects. Moreover, ABA was specifically induced by Xcc infection in Wanjincheng orange (S) but not in Jindan (R). Thus, Xcc appeared to hijack host ABA biosynthesis to promote JA accumulation, which in turn suppressed effectual SA-mediated defenses to favor disease development in citrus. Our findings provide new insights into the molecular mechanisms underlying the differential citrus-canker resistance in citrus cultivars, and a new strategy for the biotechnological improvement of citrus canker resistance was discussed.
茉莉酸（JA）和水杨酸（SA）之间的拮抗作用在植物对病原体感染的免疫微调中起着关键作用。在本研究中，我们比较了柑橘溃疡病易感（S）品种温州蜜柑（Citrus reticulata Blanco cv. Wanjincheng）和抗病（R）品种锦橙（Citrus sinensis cv. Jindan）对柑橘溃疡病菌（Xanthomonas citri subsp. citri，Xcc）的植物激素反应。在感染Xcc后，SA和JA分别在锦橙（R）和温州蜜柑（S）中被强烈诱导，并且JA似乎通过拮抗SA介导的有效防御而导致柑橘易感性。一个编码丙二烯氧化物合酶（AOS）1-2酶的同源基因，该酶催化JA生物合成的第一步，在温州蜜柑（S）中特异性上调，但在锦橙（R）中没有。启动子序列分析表明，脱落酸（ABA）响应元件在温州蜜柑（S）的启动子中富集，但在锦橙（R）中没有。因此，ABA处理可以诱导该基因表达和JA积累，导致温州蜜柑（S）的柑橘易感性增强，而合成抑制剂钨酸钠则有相反的效果。此外，ABA在温州蜜柑（S）中被Xcc感染特异性诱导，但在锦橙（R）中没有。因此，Xcc似乎劫持宿主ABA生物合成以促进JA积累，这反过来又抑制了有效的SA介导的防御，从而有利于柑橘溃疡病的发展。我们的研究结果为柑橘品种对柑橘溃疡病抗性差异的分子机制提供了新的见解，并讨论了生物技术改良柑橘溃疡病抗性的新策略。
