1 Department of Plant Pathology, Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd., Lake Alfred 33850, U.S.A.; and.
2 Department of Agricultural Botany, Faculty of Agriculture, Tanta University, Tanta, Egypt.
Mol Plant Microbe Interact. 2017 Jul;30(7):543-556. doi: 10.1094/MPMI-02-17-0045-R. Epub 2017 May 8.
Huanglongbing (HLB) is currently the largest threat to global citrus production. We examined the effect of HLB pathogen 'Candidatus Liberibacter asiaticus' infection or infestation by its vector, Diaphorina citri, on 'Valencia' sweet orange leaf pigments using high-performance liquid chromatography, followed by gene expression analysis for 46 involved genes in carotenoid and chlorophyll biosynthesis pathways. Both 'Ca. L. asiaticus' and D. citri alter the total citrus leaf pigment balance with a greater impact by 'Ca. L. asiaticus'. Although zeaxanthin was accumulated in 'Ca. L. asiaticus'-infected leaves, chlorophyllide a was increased in D. citri-infested plants. Our findings support the idea that both 'Ca. L. asiaticus' and D. citri affect the citrus pigments and promote symptom development but using two different mechanisms. 'Ca. L. asiaticus' promotes chlorophyll degradation but accelerates the biosynthesis of carotenoid pigments, resulting in accumulation of abscisic acid and its precursor, zeaxanthin. Zeaxanthin also has a photoprotective role. By contrast, D. citri induced the degradation of most carotenoids and accelerated chlorophyll biosynthesis, leading to chlorophyllide a accumulation. Chlorophyllide a might have an antiherbivory role. Accordingly, we suggest that citrus plants try to defend themselves against 'Ca. L. asiaticus' or D. citri using multifaceted defense systems, based on the stressor type. These findings will help in better understanding the tritrophic interactions among plant, pathogen, and vector.
黄龙病（HLB）是目前全球柑橘生产面临的最大威胁。我们使用高效液相色谱法检查了 HLB 病原体“亚洲韧皮杆菌”感染或其载体柑橘木虱侵染对‘瓦伦西亚’甜橙叶片色素的影响，随后对 46 个参与类胡萝卜素和叶绿素生物合成途径的基因进行了表达分析。“Ca. L. asiaticus”和 D. citri 都改变了柑橘总叶片色素平衡，“Ca. L. asiaticus”的影响更大。尽管叶黄素在“Ca. L. asiaticus”感染的叶片中积累，但在 D. citri 侵染的植物中叶绿素 a 增加。我们的研究结果支持以下观点，即“Ca. L. asiaticus”和 D. citri 都影响柑橘色素并促进症状发展，但使用两种不同的机制。“Ca. L. asiaticus”促进叶绿素降解，但加速类胡萝卜素色素的生物合成，导致脱落酸及其前体叶黄素的积累。叶黄素也具有光保护作用。相比之下，D. citri 诱导大多数类胡萝卜素的降解并加速叶绿素的生物合成，导致叶绿素 a 的积累。叶绿素 a 可能具有抗食草作用。因此，我们建议柑橘植物根据胁迫类型，利用多方面的防御系统来对抗“Ca. L. asiaticus”或 D. citri。这些发现将有助于更好地理解植物、病原体和载体之间的三营养关系。
