Huanglongbing (HLB), previously known as citrus greening disease, is a devastating disease caused by gram negative, phloem-limited, fastidious bacteria Candidatus Liberibacter spp. HLB exists in nearly all commercially cultivated citrus, causing losses to growers by affecting tree vigor, production, fruit development, and quality. Recently, some promising HLB-tolerant germplasm has been identified, and showed particularly high concentration of metabolites, such as flavone, flavanone, aldehyde, and monoterpene. This review focuses on the citrus metabolic response against the HLB and we have summarized a comprehensive metabolic pathway that is activated in response to HLB. The antibacterial role of these metabolites, which were high in the HLB tolerant varieties are discussed. Generally, most of the amino acids, flavonoids, terpenes, and volatile compounds were significantly higher, even hundreds times of increase, in HLB-tolerant varieties. We also summarized the secondary metabolites, which were differentially altered in leaves, fruits, phloem sap (stem), and roots of infected citrus plants. Different metabolic studies have suggested that particular metabolites may play vital role in restricting the movement and multiplication of pathogens. Moreover, these metabolic signatures can be developed into tolerance markers against HLB. Genome-editing technologies should be used to confirm the functions of candidate genes responsible for increased production of compounds related to HLB tolerance. Engineering the metabolic pathways to create an ideal combination of gene alleles to propel metabolite flow for the antimicrobial activities, is an alternative tool to breed tolerant cultivars against HLB.

中文翻译：

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宿主物种对柑橘黄龙病（绿化病）的代谢机制

黄龙病（HLB），以前称为柑橘绿化病，是一种由克氏阴性，韧皮部有限，挑食性细菌念珠菌引起的毁灭性疾病。Liberibacter spp。HLB几乎存在于所有商业种植的柑橘中，通过影响树木的活力，产量，果实发育和品质，对种植者造成损失。最近，已经鉴定出一些有前途的HLB耐受性种质，并显示出特别高浓度的代谢物，例如黄酮，黄烷酮，醛和单萜。这篇综述集中在针对HLB的柑橘代谢反应上，我们总结了响应HLB活化的综合代谢途径。讨论了这些代谢物的抗菌作用，这些代谢物在HLB耐性品种中较高。通常，在耐HLB的品种中，大多数氨基酸，类黄酮，萜烯和挥发性化合物均显着较高，甚至增加了数百倍。我们还总结了次级代谢产物，在被感染的柑橘类植物的叶片，果实，韧皮部汁液（茎）和根中有不同的变化。不同的代谢研究表明，特定的代谢产物可能在限制病原体的运动和繁殖方面起着至关重要的作用。而且，这些代谢特征可以发展为针对HLB的耐受性标记。应该使用基因组编辑技术来确认候选基因的功能，这些候选基因负责增加与HLB耐受性相关的化合物的产量。设计代谢途径以创建基因等位基因的理想组合，以促进代谢物的流动以实现抗菌活性，是育种对HLB耐受的品种的替代工具。不同的代谢研究表明，特定的代谢产物可能在限制病原体的运动和繁殖方面起着至关重要的作用。而且，这些代谢特征可以发展为针对HLB的耐受性标记。应该使用基因组编辑技术来确认候选基因的功能，这些候选基因负责增加与HLB耐受性相关的化合物的产量。设计代谢途径以创建基因等位基因的理想组合，以促进代谢物的流动以实现抗菌活性，是育种对HLB耐受的品种的替代工具。不同的代谢研究表明，特定的代谢产物可能在限制病原体的运动和繁殖方面起着至关重要的作用。而且，这些代谢特征可以发展为针对HLB的耐受性标记。应该使用基因组编辑技术来确认候选基因的功能，这些候选基因负责增加与HLB耐受性相关的化合物的产量。设计代谢途径以创建基因等位基因的理想组合，以促进代谢物的流动以实现抗菌活性，是育种对HLB耐受的品种的替代工具。应该使用基因组编辑技术来确认候选基因的功能，这些候选基因负责增加与HLB耐受性相关的化合物的产量。设计代谢途径以创建基因等位基因的理想组合，以推动代谢物的流动以实现抗菌活性，是育种对HLB耐受的品种的替代工具。应该使用基因组编辑技术来确认候选基因的功能，这些候选基因负责增加与HLB耐受性相关的化合物的产量。设计代谢途径以创建基因等位基因的理想组合，以促进代谢物的流动以实现抗菌活性，是育种对HLB耐受的品种的替代工具。