Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, Florida 33850.
Department of Agricultural Botany, Faculty of Agriculture, Tanta University, 31512 Tanta, Egypt.
Plant Physiol. 2020 Dec;184(4):2216-2239. doi: 10.1104/pp.20.00393. Epub 2020 Aug 25.
Huanglongbing (HLB) is a devastating citrus disease worldwide that is putatively caused by Liberibacter asiaticus and transmitted by Melatonin is a ubiquitously distributed auxin-like metabolite found in both prokaryotes and eukaryotes. In this study, we used integrative metabolomic and transcriptomic approaches to investigate the potential role of melatonin in citrus response against HLB and to understand the relationships between melatonin and the stress-associated phytohormones at molecular and metabolic levels. Melatonin was detected in the leaves of Valencia sweet orange () after derivatization with -methyl--trimethylsilyltrifluoroacetamide using a targeted gas chromatography-mass spectrometry running in selective ion monitoring mode-based method. L. asiaticus infection and infestation significantly increased endogenous melatonin levels in Valencia sweet orange leaves and upregulated the expression of its biosynthetic genes (, , , , and ). However, infection with L. asiaticus had a greater effect than did infestation with Melatonin induction was positively correlated with salicylic acid content, but not that of trans-jasmonic acid. Moreover, melatonin supplementation enhanced the endogenous contents of the stress-associated phytohormones (salicylates, auxins, trans-jasmonic acid, and abscisic acid) and the transcript levels of their biosynthetic genes. Furthermore, melatonin supplementation diminished the L. asiaticus titer within the infected leaves, which suggests that melatonin might play an antibacterial role against this bacterium and gram-negative bacteria in general. These findings provide a better understanding of the melatonin-mediated defensive response against HLB via modulation of multiple hormonal pathways. Understanding the role of melatonin in citrus defense to HLB may provide a novel therapeutic strategy to mitigate the disease.
黄龙病（HLB）是一种全球性的毁灭性柑橘病害，据推测是由亚洲韧皮杆菌引起的，并通过传播。褪黑素是一种普遍存在的、类似于生长素的代谢物，存在于原核生物和真核生物中。在这项研究中，我们使用整合代谢组学和转录组学方法来研究褪黑素在柑橘对 HLB 反应中的潜在作用，并在分子和代谢水平上理解褪黑素与应激相关植物激素之间的关系。使用衍生化方法（-甲基--三甲硅基三氟乙酰胺），通过基于选择性离子监测模式的靶向气相色谱-质谱法，在瓦伦西亚甜橙（）叶片中检测到褪黑素。亚洲韧皮杆菌感染和实蝇侵害显著增加了瓦伦西亚甜橙叶片中的内源褪黑素水平，并上调了其生物合成基因（、、、和）的表达。然而，感染亚洲韧皮杆菌比实蝇侵害的影响更大。褪黑素诱导与水杨酸含量呈正相关，但与反式茉莉酸含量无关。此外，褪黑素的补充增强了应激相关植物激素（水杨酸、生长素、反式茉莉酸和脱落酸）的内源性含量和生物合成基因的转录水平。此外，褪黑素的补充降低了感染叶片中的亚洲韧皮杆菌滴度，这表明褪黑素可能对这种细菌和一般革兰氏阴性菌具有抗菌作用。这些发现通过调节多种激素途径，提供了对褪黑素介导的柑橘抗 HLB 防御反应的更好理解。了解褪黑素在柑橘防御 HLB 中的作用可能为减轻该疾病提供一种新的治疗策略。
