Shotgun Proteomic Analysis of the Mexican Lime Tree Infected with “<i>Candidatus</i> <i>Phytoplasma aurantifolia</i>”

Infection of Mexican lime trees (Citrus aurantifolia L.) with the specialized bacterium “Candidatus Phytoplasma aurantifolia” causes witches’ broom disease. Witches’ broom disease has the potential to cause significant economic losses throughout western Asia and North Africa. We used label-free quantitative shotgun proteomics to study changes in the proteome of Mexican lime trees in response to infection by “Ca. Phytoplasma aurantifolia”. Of 990 proteins present in five replicates of healthy and infected plants, the abundances of 448 proteins changed significantly in response to phytoplasma infection. Of these, 274 proteins were less abundant in infected plants than in healthy plants, and 174 proteins were more abundant in infected plants than in healthy plants. These 448 proteins were involved in stress response, metabolism, growth and development, signal transduction, photosynthesis, cell cycle, and cell wall organization. Our results suggest that proteomic changes in response to infection by phytoplasmas might support phytoplasma nutrition by promoting alterations in the host’s sugar metabolism, cell wall biosynthesis, and expression of defense-related proteins. Regulation of defense-related pathways suggests that defense compounds are induced in interactions with susceptible as well as resistant hosts, with the main differences between the two interactions being the speed and intensity of the response.墨西哥莱檬树（Citrus aurantifolia L.）被专性细菌"Candidatus Phytoplasma aurantifolia"侵染后，会引发丛枝病。该丛枝病在西亚与北非地区均可能造成严重的经济损失。本研究采用无标记定量鸟枪法蛋白质组学（label-free quantitative shotgun proteomics），探究墨西哥莱檬树在被"Ca. Phytoplasma aurantifolia"侵染后的蛋白质组变化。在健康与侵染植株各5次生物学重复中鉴定到的990种蛋白质里，有448种蛋白质的丰度在植原体侵染后发生了显著变化。其中，274种蛋白质在侵染植株中的丰度低于健康植株，剩余174种则在侵染植株中丰度更高。这448种蛋白质涉及应激响应、代谢、生长发育、信号转导、光合作用、细胞周期以及细胞壁组织等生物学过程。本研究结果表明，植原体侵染诱导的蛋白质组变化，可通过调控宿主糖代谢、细胞壁生物合成以及防卫相关蛋白质的表达，为植原体的营养需求提供支持。防卫相关通路的调控规律显示，在与感病寄主和抗病寄主的互作中，防卫化合物均会被诱导产生，二者的主要差异在于响应速度与响应强度。