Huanglongbing (HLB) is the most devastating and widespread citrus disease. All commercial citrus varieties are susceptible to the HLB-associated bacterium, Candidatus Liberibacter asiaticus (CLas), which resides in the phloem. The phloem is part of the plant vascular system and is involved in sugar transport. To investigate the plant response to CLas, we enriched for proteins surrounding the phloem in an HLB susceptible sweet orange variety, Washington navel (Citrus sinensis (L) Osbeck). Quantitative proteomics revealed global changes in the citrus proteome after CLas inoculation. Plant metabolism and translation were suppressed, while defense-related proteins such as peroxidases, proteases and protease inhibitors were induced in the vasculature. Transcript accumulation and enzymatic activity of plant peroxidases in CLas infected sweet orange varieties under greenhouse and field conditions were assessed. While peroxidase transcript accumulation was induced in CLas infected sweet orange varieties, peroxidase enzymatic activity varied. Specific serine proteases were upregulated in Washington navel in the presence of CLas based on quantitative proteomics. Subsequent activity-based protein profiling revealed increased activity of two serine proteases, and reduced activity of one protease in two C. sinensis sweet orange varieties under greenhouse and field conditions. The observations in the current study highlight global reprogramming of the citrus vascular proteome and differential regulation of enzyme classes in response to CLas infection. These results open an avenue for further investigation of diverse responses to HLB across different environmental conditions and citrus genotypes.

中文翻译：

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柑橘类血管蛋白质组学突出了黄龙病病情发展过程中过氧化物酶和丝氨酸蛋白酶的作用

黄龙病（HLB）是最具破坏性和最广泛的柑橘类疾病。所有商业柑橘品种都对位于韧皮部的HLB相关细菌亚洲念珠菌（CLas）敏感。韧皮部是植物血管系统的一部分，参与糖的运输。为了调查植物对CLas的反应，我们富集了HLB敏感甜橙品种华盛顿脐橙（Citrus sinensis（L）Osbeck）韧皮部周围的蛋白质。定量蛋白质组学揭示了CLas接种后柑橘类蛋白质组的整体变化。植物的新陈代谢和翻译受到抑制，而与防御相关的蛋白质（例如过氧化物酶，蛋白酶和蛋白酶抑制剂）在脉管系统中被诱导。在温室和田间条件下，评估了在CLas感染的甜橙品种中植物过氧化物酶的转录产物积累和酶活性。虽然在CLas感染的甜橙品种中诱导了过氧化物酶转录本的积累，但过氧化物酶的酶活性却发生了变化。基于定量蛋白质组学，在CLas存在下，在华盛顿肚脐中特异性丝氨酸蛋白酶被上调。随后的基于活动的蛋白质谱分析表明，在温室和田间条件下，两种丝氨酸甜橙品种中两种丝氨酸蛋白酶的活性增加，而一种蛋白酶的活性降低。本研究中的观察结果突出了柑橘血管蛋白质组的全球重编程以及对CLas感染作出反应的酶类别的差异调节。