Sétamou Mamoudou, Alabi Olufemi J, Simpson Catherine R, Jifon John L
Texas A&M University-Kingsville Citrus Center, Weslaco, United States of America.
Department of Plant Pathology & Microbiology, Texas A&M AgriLife Research and Extension Center, Weslaco, TX, United States of America.
PLoS One. 2017 Dec 13;12(12):e0187921. doi: 10.1371/journal.pone.0187921. eCollection 2017.
Huanglongbing is a devastating disease of citrus. In this study, a comprehensive profile of phloem sap amino acids (AA) in four permissive host plants of Candidatus Liberibacter asiaticus (CLas) and three non-permissive Rutaceae plants was conducted to gain a better understanding of host factors that may promote or suppress the bacterium. The AA profiles of Diaphorina citri nymphs and adults were similarly analyzed. A total of 38 unique AAs were detected in phloem sap of the various plants and D. citri samples, with phloem sap of young shoots containing more AAs and at higher concentrations than their mature counterparts. All AAs detected in phloem sap of non-permissive plants were also present in CLas -permissive hosts plus additional AAs in the latter class of plants. However, the relative composition of 18 commonly shared AAs varied between CLas -permissive hosts and non-permissive plants. Multivariate analysis with a partial least square discriminant methodology revealed a total of 12 AAs as major factors affecting CLas host status, of which seven were positively related to CLas tolerance/resistance and five positively associated with CLas susceptibility. Most of the AAs positively associated with CLas susceptibility were predominantly of the glutamate family, notably stressed-induced AAs such as arginine, GABA and proline. In contrast, AAs positively correlated with CLas tolerance/resistance were mainly of the serine family. Further analysis revealed that whereas the relative proportions of AAs positively associated with CLas susceptibility did not vary with host developmental stages, those associated with CLas tolerance/resistance increased with flush shoot maturity. Significantly, the proline-to-glycine ratio was determined to be an important discriminating factor for CLas permissivity with higher values characteristic of CLas -permissive hosts. This ratio could be exploited as a biomarker in HLB-resistance breeding programs.
黄龙病是柑橘的一种毁灭性病害。在本研究中，对亚洲韧皮杆菌（CLas）的四种适宜寄主植物和三种非适宜芸香科植物的韧皮部汁液氨基酸（AA）进行了全面分析，以更好地了解可能促进或抑制该细菌的寄主因素。对柑橘木虱若虫和成虫的氨基酸谱也进行了类似分析。在各种植物和柑橘木虱样本的韧皮部汁液中总共检测到38种独特的氨基酸，幼嫩梢的韧皮部汁液比成熟梢含有更多且浓度更高的氨基酸。在非适宜寄主植物韧皮部汁液中检测到的所有氨基酸在CLas适宜寄主中也都存在，并且后一类植物中还有额外的氨基酸。然而，18种常见共享氨基酸的相对组成在CLas适宜寄主和非适宜植物之间有所不同。采用偏最小二乘判别法进行多变量分析，共发现12种氨基酸是影响CLas寄主状态的主要因素，其中7种与CLas耐受性/抗性呈正相关，5种与CLas易感性呈正相关。与CLas易感性呈正相关的大多数氨基酸主要属于谷氨酸家族，特别是应激诱导的氨基酸，如精氨酸、γ-氨基丁酸和脯氨酸。相比之下，与CLas耐受性/抗性呈正相关的氨基酸主要属于丝氨酸家族。进一步分析表明，与CLas易感性呈正相关的氨基酸相对比例不随寄主发育阶段而变化，而与CLas耐受性/抗性相关的氨基酸比例则随着新梢成熟而增加。值得注意的是，脯氨酸与甘氨酸的比例被确定为CLas适宜性的一个重要判别因素，CLas适宜寄主的该比例值更高。该比例可作为黄龙病抗性育种计划中的一个生物标志物。
