Huanglongbing (HLB) is one of the most serious citrus diseases, caused by phloem limited endophytic bacteria Candidatus Liberibacter asiaticus (Clas), affecting worldwide citrus production. Metabolomics approaches were employed to gain insight into mechanisms involved in defense against Clas in endophyte Bacillus subtilis L1-21 treated diseased and healthy citrus plants. Using LC-ESI-MS/MS, we compared the metabolic profile of citrus plants before and after treatment with endophyte L1-21. Our analysis indicated large differences in citrus metabolites after endophyte L1-21 application. In total, seven hundred and fourty two metabolites were detected with highest percentage recorded for organic acids, flavone, amino acid derivatives, flavone C-glycosides, nucleotide derivatives, and flavonol. Interestingly, differentially expressed metabolites (DEMs) analysis revealed the amino acids, such as lysine and tyrosine which are involved in plant defense agianst pathogen attack were regulated in diseased citrus plants after endophyte application (padj<0.05). In addition, other important metabolites up-regulated were xanthine, leucic acid, and α-Linolenic acid implicated in different plant defense pathways against Clas. Furhter, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed important pathways related to purine metabolism, biotin metabolism, and betalain biosynthesis, terpenoid-quinone biosynthesis, phenylalanine, tyrosine and lysine biosynthesis, isoflavonoid biosynthesis (padj<0.05). Taken together, this is the first study using native endophytes in diseased and healthy state of citrus which has proven to be useful in disease management by strengthening the defense of citrus to Clas pathogen.

黄龙病（HLB）是最严重的柑橘类疾病之一，由韧皮部有限的内生细菌Candidatus Liberibacter asiaticus（C las）引起，影响了全世界的柑橘生产。代谢组学方法被采用，以深入了解参与了对防御机制Ç拉斯在植物内生菌枯草芽孢杆菌L1-21处理了病态和健康的柑橘类植物。使用LC-ESI-MS / MS，我们比较了用内生菌L1-21处理前后的柑橘类植物的代谢状况。我们的分析表明，应用内生菌L1-21后，柑橘代谢产物差异很大。总共检测到742种代谢产物，其中有机酸，黄酮，氨基酸衍生物，黄酮C-糖苷，核苷酸衍生物和黄酮醇的记录百分比最高。有趣的是，差异表达代谢物（DEMs）分析显示，在施用内生菌后，病变柑橘类植物中参与植物防御蠕虫病原体侵袭的氨基酸如赖氨酸和酪氨酸受到调节（padj <0.05）。此外，其他上调的重要代谢物是黄嘌呤，白氨酸，Ç拉斯。Furhter的《京都基因与基因组百科全书》（KEGG）富集分析揭示了与嘌呤代谢，生物素代谢和甜菜碱生物合成，萜类醌-醌生物合成，苯丙氨酸，酪氨酸和赖氨酸生物合成，异黄酮类生物合成相关的重要途径（padj <0.05）。总之，这是使用已被证明是在疾病管理有用的柑橘患病和健康状态本土内生菌通过加强柑橘的防守第一项研究Ç拉斯病原体。