关键词: 柑橘, 柑橘黄龙病, 亚洲柑橘木虱, 病原增殖, 传播机制, 免疫调控

Abstract: Citrus huanglongbing, caused by the phloem-limited Candidatus Liberibacter asiaticus (CLas), is a major quarantine disease of citrus. In nature, the pathogen is mainly transmitted by the Asian citrus psyllid (Diaphorina citri) in a persistent propagative manner. In this review, we systematically summarized the research progress on the interactions among CLas, the host citrus and the insect vector D. citri. In 2009, the complete genome of CLas was obtained from a single citrus psyllid, and 86 Sec-dependent secreted proteins were identified. D. citri nymphs exhibit higher CLas acquisition and transmission efficiency than adults, with 25 ℃ being the optimal temperature for CLas acquisition by the vector. The CLas infection cycle within D. citri lasts 15-20 d. CLas enters D. citri cells via clathrin-mediated endocytosis, forms Liberibacter-containing vacuoles (LCVs), and utilizes its outer membrane proteins (OMPs) to reshape gut actin protein and overcome midgut barriers. Furthermore, CLas enhances the fecundity of D. citri to promote transmission by regulating the juvenile hormone (JH), adipokinetic hormone (AKH) and vitellogenin receptor (VgR) pathways, and related microRNAs. To counteract D. citri innate immunity, CLas achieves immune evasion by inducing mild autophagy through interaction with the autophagy-related proteins ATG8/ATG14 of D. citri and inhibiting the melanization-related PGRP-CLIP1-CLIP4-PPO-PO signaling cascade via its effector protein SDE3230. In the CLas-citrus-D. citri tripartite interaction, CLas infection manipulates the synthesis of citrus volatile compounds to attract D. citri for feeding. In response, D. citri secretes salivary effectors to suppress citrus immune pathways, thereby facilitating pathogen spread. Current research has not yet clarified the key scientific issues such as CLas proliferation, host-pathogen immune game, and LCV formation in D. citri. Future research should focus on three key areas, including the molecular mechanisms underlying CLas-D. citri immune homeostasis, CLas proliferation strategies within D. citri, and the signaling networks of the tripartite interactions among CLas, citrus and D. citri. Concurrently, an integrated approach involving gene editing-based germplasm improvement, AI-driven high-throughput screening of antimicrobial peptides, synthetic biology techniques and nano delivery system is proposed to develop effective prevention, control and management strategies for CLas.

Key words:  Citrus, citrus huanglongbing, Diaphorina citri, pathogen propagation, transmission mechanism, immunoregulation