柑橘黄龙病菌效应子致病机制研究进展

Research Progress on Pathogenic Mechanism of Effectors of Candidatus Liberibacter asiaticus

柑橘黄龙病(Citrus Huanglongbing,HLB)是全世界范围内为害最严重的柑橘病害之一,每年对柑橘生产造成巨大损失,严重影响全球柑橘产业发展。在中国岭南地区,重要药用植物茶枝柑、化州柚、广佛手等均受到柑橘黄龙病的威胁。亚洲韧皮部杆菌(Candidatus Liberibacter asiaticus,CLas)是最常见的柑橘黄龙病致病菌株,该菌定殖于植物的韧皮部,主要感染芸香科柑橘属(CitrusL.)植物。目前尚无体外成功培养亚洲韧皮部杆菌的报道,因此对柑橘黄龙病致病机制研究和黄龙病防治均有较高难度。效应子(又称效应蛋白)是病原菌向宿主分泌的一类致病因子,是病原菌侵染植物的重要武器。效应子能够靶向宿主细胞关键免疫信号转导和调控组分,从而抑制植物防御反应,增强病原菌致病性。柑橘黄龙病菌能够分泌近百个效应子,根据分泌途径的不同,主要分为Sec依赖型效应子和非经典分泌效应子,其中Sec依赖型效应子有90个、非经典分泌效应子有15个。这些效应子在柑橘黄龙病菌侵染宿主过程中发挥关键作用。已有研究发现,黄龙病菌效应子能够靶向包括植物免疫信号转导、细胞自噬、水杨酸信号途径等多个生物学过程,从而干扰宿主柑橘的防御反应,以促进黄龙病菌的定殖。该文结合近年来有关柑橘黄龙病菌效应子致病机制的研究,阐述了柑橘黄龙病研究概况、黄龙病菌效应子的分类,重点综述了影响柑橘防御反应的柑橘黄龙病菌效应子的致病机制,最后展望了黄龙病菌效应子的未来研究趋势和方向,讨论了基于效应子靶标寻找黄龙病重要抗性基因的可能性,期望通过亚洲韧皮部杆菌效应子研究,为柑橘黄龙病致病机制研究和病害防控提供指导。

Citrus Huanglongbing(HLB)is one of the most serious citrus diseases worldwide,causing huge economic losses every year and seriously affecting the development of the global citrus industry.In Lingnan region of China,HLB threatens the growth of important medicinal plants,such as Citrus reticulata‘Chachi’,C.grandis‘Tomentosa’,and C.medica‘Fingered’.Candidatus Liberibacter asiaticus(CLas)is the most common pathogen,which colonizes the phloem of plants and mainly infects rutaceae citrus species.At present,there is a lack of reports on the successful cultivation of CLas in vitro,making it difficult to study the pathogenic mechanism and control of the disease.Effector(also called effector protein)is a kind of pathogenic factor secreted by pathogens to the host,serving as an important weapon for pathogens to infect plants.The effectors are capable of targeting the key immune signal transduction and regulatory components of host cells,thereby inhibiting plant defense responses and enhancing the pathogenicity of pathogens.CLas can secrete over a hundred effectors,mainly divided into Sec-dependent effectors and non-classical secretory effectors according to different secretion pathways.Among them,there are 90 Sec-dependent effectors and 15 non-classical secretory effectors.They play a key role in the pathogenic process of infecting the host.Studies have shown that HLB effectors could target multiple cellular processes including plant immune signal transduction,autophagy,salicylic acid signaling pathway,and seriously disrupt the host’s defense response to achieve colonization.Combined with recent researches on the pathogenic mechanism of HLB effectors,this article elaborates on the research overview of HLB and the classification of HLB effectors,and summarizes the pathogenic mechanism of effectors that affect citrus defense response.Finally,it offers a prospect on the future research directions,discusses the possibility of searching for important resistance genes to HLB based on identification of effector targets,with a aim to provide guidance for the pathogenic mechanism and disease control of HLB through the study of the effectors.