Pitino Marco, Armstrong Cheryl M, Duan Yongping
USDA-ARS, US Horticultural Research Laboratory, 2001 S. Rock Road, Fort Pierce, 34945 FL USA.
Hortic Res. 2017 Aug 23;4:17040. doi: 10.1038/hortres.2017.40. eCollection 2017.
Liberibacter asiaticus (Las) is a fastidious, phloem-restricted pathogen with a significantly reduced genome, and attacks all citrus species with no immune cultivars documented to date. Like other plant bacterial pathogens, Las deploys effector proteins into the organelles of plant cells, such as mitochondria and chloroplasts to manipulate host immunity and physiology. These organelles are responsible for the synthesis of adenosine triphosphate (ATP) and have a critical role in plant immune signaling during hydrogen peroxide (HO) production. In this study, we investigated HO and ATP accumulation in relation to citrus huanglongbing (HLB) in addition to revealing the expression profiles of genes critical for the production and detoxification of HO and ATP synthesis. We also found that as ATP and HO concentrations increased in the leaf, so did the severity of the HLB symptoms, a trend that remained consistent among the four different citrus varieties tested. Furthermore, the upregulation of ATP synthase, a key enzyme for energy conversion, may contribute to the accumulation of ATP in infected tissues, whereas downregulation of the HO detoxification system may cause oxidative damage to plant macromolecules and cell structures. This may explain the cause of some of the HLB symptoms such as chlorosis or leaf discoloration. The findings in this study highlight important molecular and physiological mechanisms involved in the host plants' response to Las infection and provide new targets for interrupting the disease cycle.
亚洲韧皮杆菌（Las）是一种苛求的、局限于韧皮部的病原体，其基因组显著缩减，能侵袭所有柑橘品种，迄今为止尚无免疫品种的记载。与其他植物细菌病原体一样，Las将效应蛋白分泌到植物细胞的细胞器中，如线粒体和叶绿体，以操纵宿主的免疫和生理机能。这些细胞器负责三磷酸腺苷（ATP）的合成，在过氧化氢（H₂O₂）产生过程中的植物免疫信号传导中起关键作用。在本研究中，我们除了揭示对H₂O₂产生、解毒及ATP合成至关重要的基因的表达谱外，还研究了与柑橘黄龙病（HLB）相关的H₂O₂和ATP积累情况。我们还发现，随着叶片中ATP和H₂O₂浓度的增加，HLB症状的严重程度也随之增加，这一趋势在所测试的四个不同柑橘品种中保持一致。此外，能量转换的关键酶ATP合酶的上调可能导致感染组织中ATP的积累，而H₂O₂解毒系统的下调可能会对植物大分子和细胞结构造成氧化损伤。这可能解释了一些HLB症状的成因，如黄化或叶片变色。本研究结果突出了宿主植物对Las感染反应中涉及的重要分子和生理机制，并为中断疾病循环提供了新的靶点。
