National Citrus Engineering Research Center, Citrus Research Institute, Southwest University, Chongqing, China.
Mol Plant Pathol. 2022 Jul;23(7):1022-1034. doi: 10.1111/mpp.13206. Epub 2022 Mar 13.
Huanglongbing (HLB), associated with "Candidatus Liberibacter asiaticus" (CLas), is a globally devastating plant disease. The highly reduced genome of CLas encodes a number of secretory proteins. The conserved prophage-encoded protein AGH17470 is herein identified as a nonclassical secretory protein. We confirmed that the N-terminal and C-terminal sequences jointly determine the secretion of AGH17470. The transient expression of AGH17470 protein in Nicotiana benthamiana caused hypersensitive response (HR) cell death in infiltrated leaves and systemically infected leaves as well as the dwarfing of the entire plant, suggesting that AGH17470 is involved in the plant immune response, growth, and development. Overexpression of AGH17470 in N. benthamiana and citrus plants up-regulated the transcription of pathogenesis-related and salicylic acid (SA)-signalling pathway genes and promoted SA accumulation. Furthermore, transient expression of AGH17470 enhanced the resistance of sweet orange to Xanthomonas citri subsp. citri. To our knowledge, AGH17470 is the first prophage-encoded secretory protein demonstrated to elicit an HR and induce a strong plant immune response. The findings have increased our understanding of prophage-encoded secretory protein genes, and the results provide clues as to the plant defence response against CLas.
黄龙病（HLB）与“亚洲韧皮杆菌”（CLas）有关，是一种全球性的破坏性植物疾病。CLas 的高度简化基因组编码了许多分泌蛋白。保守的前噬菌体编码蛋白 AGH17470 被鉴定为一种非经典分泌蛋白。我们证实，N 端和 C 端序列共同决定了 AGH17470 的分泌。AGH17470 蛋白在本氏烟中的瞬时表达导致了浸润叶片和系统感染叶片的过敏反应（HR）细胞死亡，以及整个植株的矮化，表明 AGH17470 参与了植物的免疫反应、生长和发育。在本氏烟和柑橘植物中超表达 AGH17470 上调了病程相关和水杨酸（SA）信号通路基因的转录，并促进了 SA 的积累。此外，AGH17470 的瞬时表达增强了甜橙对柑橘黄龙病菌的抗性。据我们所知，AGH17470 是第一个被证明能引起过敏反应并诱导强烈植物免疫反应的前噬菌体编码分泌蛋白。这些发现增加了我们对前噬菌体编码分泌蛋白基因的理解，并为植物对 CLas 的防御反应提供了线索。
