Centro de Citricultura Sylvio Moreira, Instituto Agronômico de Campinas, Cordeirópolis, São Paulo, Brazil.
BMC Genomics. 2013 Apr 12;14:247. doi: 10.1186/1471-2164-14-247.
Citrus huanglongbing (HLB) disease is caused by endogenous, phloem-restricted, Gram negative, uncultured bacteria named Candidatus Liberibacter africanus (CaLaf), Ca. L. asiaticus (CaLas), and Ca. L. americanus (CaLam), depending on the continent where the bacteria were first detected. The Asian citrus psyllid vector, Diaphorina citri, transmits CaLas and CaLam and both Liberibacter species are present in Brazil. Several studies of the transcriptional response of citrus plants manifesting HLB symptoms have been reported, but only for CaLas infection. This study evaluated the transcriptional reprogramming of a susceptible genotype of sweet orange challenged with CaLam, using a customized 385K microarray containing approximately 32,000 unigene transcripts. We analyzed global changes in gene expression of CaLam-infected leaves of sweet orange during the symptomatic stage of infection and compared the results with previously published microarray studies that used CaLas-infected plants. Twenty candidate genes were selected to validate the expression profiles in symptomatic and asymptomatic PCR-positive leaves infected with CaLas or CaLam.
The microarray analysis identified 633 differentially expressed genes during the symptomatic stage of CaLam infection. Among them, 418 (66%) were upregulated and 215 (34%) were down regulated. Five hundred and fourteen genes (81%) were orthologs of genes from Arabidopsis thaliana. Gene set enrichment analysis (GSEA) revealed that several of the transcripts encoded transporters associated with the endomembrane system, especially zinc transport. Among the most biologically relevant gene transcripts in GSEA were those related to signaling, metabolism and/or stimulus to hormones, genes responding to stress and pathogenesis, biosynthesis of secondary metabolites, oxidative stress and transcription factors belonging to different families. Real time PCR of 20 candidate genes validated the expression pattern of some genes in symptomatic and asymptomatic leaves infected with CaLam or CaLas.
Many gene transcripts and biological processes are significantly altered upon CaLam infection. Some of them had been identified in response to CaLas infection, while others had not been previously reported. These data will be useful for selecting target genes for genetic engineering to control HLB.
黄龙病是由内共生的、韧皮部限制的、革兰氏阴性、未培养的细菌引起的，这些细菌被命名为非洲韧皮部杆菌（CaLaf）、亚洲韧皮部杆菌（CaLas）和美洲韧皮部杆菌（CaLam），具体取决于首次检测到细菌的大陆。亚洲柑橘木虱作为柑橘黄龙病的传播媒介，传播 CaLas 和 CaLam，而这两种韧皮部杆菌都存在于巴西。已经有几项关于表现黄龙病症状的柑橘植物转录反应的研究报告，但仅针对 CaLas 感染。本研究使用包含大约 32000 个单基因转录本的定制 385K 微阵列，评估了感病基因型甜橙受到 CaLam 挑战时的转录重编程。我们分析了感染期感染甜橙叶片中 CaLam 感染的基因表达的全局变化，并将结果与之前使用 CaLas 感染植物的微阵列研究进行了比较。选择了 20 个候选基因，以验证感染 CaLas 或 CaLam 的无症状和 PCR 阳性叶片的表达谱。
微阵列分析在 CaLam 感染的症状阶段鉴定了 633 个差异表达基因。其中，418 个（66%）上调，215 个（34%）下调。514 个基因（81%）是拟南芥同源基因。基因集富集分析（GSEA）显示，一些转录本编码与内质网系统相关的转运蛋白，特别是锌转运蛋白。在 GSEA 中最具生物学意义的基因转录本中，与信号转导、代谢和/或激素刺激、对胁迫和发病机制的反应、次生代谢物的生物合成、氧化应激和属于不同家族的转录因子相关的基因转录本。20 个候选基因的实时 PCR 验证了感染 CaLam 或 CaLas 的无症状和有症状叶片中一些基因的表达模式。
CaLam 感染会显著改变许多基因转录本和生物过程。其中一些已经被鉴定为对 CaLas 感染的反应，而其他则没有被先前报道过。这些数据将有助于选择用于遗传工程控制黄龙病的靶基因。
