Publications

4619

ABSTRACT Ubiquitin‐proteasome is a conserved mechanism that regulates cellular responses and disease resistance in plants. However, the regulatory role of ubiquitin‐proteasome in the pathogenicity of “ Candidatus Liberibacter asiaticus” ( C Las), the causal agent of citrus huanglongbing (HLB), one of the most serious citrus diseases, remains poorly defined. In this study, we demonstrated that CLIBASIA_04250 (SDE4250) suppresses 26S proteasome activity in citrus, leading to a reduction in salicylic acid (SA) levels and downregulation of SA‐responsive genes. Further investigation revealed that SDE4250 specifically targets the citrus 26S proteasome non‐ATPase regulatory subunit 4 homologue (CsRPN10) and enhances its degradation via the 26S proteasome pathway. Moreover, overexpression of CsRPN10 inhibited C Las proliferation in citrus hairy roots, which was accompanied by a significant accumulation of SA content and upregulation of related defence genes. Collectively, our findings indicate that SDE4250 targets the citrus 26S proteasome to disrupt SA‐mediated citrus immunity.

Citrus huanglongbing (HLB), associated with the bacterium ‘Candidatus Liberibacter asiaticus’ and spread by the Asian citrus psyllid (Diaphorina citri; ACP), poses a significant threat to California’s citrus industry. First identified in Los Angeles in 2012, HLB has since spread through residential areas across Southern California. A risk-based survey (RBS) model has been developed to improve HLB surveillance and intervention. Within this framework, model components change as HLB dynamics shift, requiring regular updates to maintain data accuracy and model reliability. Disease spread is influenced by natural factors, such as ACP establishment and confirmed HLB locations, as well as human-mediated factors like global mobility (travel introduction from HLB-infected countries), transportation of citrus materials, nurseries, packinghouses, farmers’ markets, and proximity to private or otherwise inaccessible lands. Human-mediated risk factors account for approximately 26.3% (18.4 to 38.4%) of HLB incidence across different years, and natural causes predominantly explain the remaining 73.7% (61.6 to 81.7%). Notably, global mobility was crucial for early HLB detection in new areas, whereas ACP density strongly correlated with disease spread once established. A retrospective analysis from 2015 to 2022 evaluated the RBS model’s performance, showing a predictive power of 88 to 97%, which confirms its validity for developing targeted interventions and early detection strategies in California.

'Candidatus Phytoplasma solani' is a distinct species of the class Mollicutes (16SrXII group), characterized by phloem-limited localization and strong host dependence. It is widely distributed, mainly in Europe, and affects over 100 plant species, including economically important crops for Moldova. The name reflects its significant impact on plants of the Solanaceae family, causing stolbur disease. It also infects grapevine, pepper, maize, lavender, and other crops. Climate change has favored the spread of the pathogen and its insect vectors into new regions and host plants. Therefore, monitoring and controlling its dissemination in economically important crops is essential. Accurate diagnosis can be achieved by molecular methods, with PCR-based techniques offering a reliable and cost-effective approach. The aim of the study was to determine the presence or absence of infection in some agricultural crops: tomato, maize, potato, pepper, eggplant, wheat, plum and apple growing in experimental fields of Institute of Genetics, Physiology and Plant Protection, MSU. Materials and methods: Various DNA extraction methods were used depending on plant culture: boiling in alkaline solution, DNAzol, SDS, CTAB. Nested PCR analysis was carried out using specific to 'Ca. P. solani' primers designed on the base of chaperonine or 16S rRNA gene sequences. Amplification results were recorded using gel agarose electrophoresis (1.5% agarose, 0.5 x TBE buffer) stained with ethidium bromide and visualized in UV. Results: A comprehensive study of tomato conducted during 2016-2025 showed the continuous presence of the pathogen, with infection rates reaching up to 72% depending on annual conditions, confirming the high susceptibility of tomato to 'Ca. P. solani'. In potato, 14.6% of plants were infected, while sweet pepper showed a much lower incidence of 4%. Overall, the results indicate the predominant distribution of the pathogen within the Solanaceae family, further supported by its detection in the ruderal species Solanum nigrum. The phytoplasma was not detected only in eggplant among the analyzed Solanaceae species. In contrast, molecular diagnostics gave negative results in crops from other families, including maize and wheat (cereals), as well as apple and plum (fruit crops). The pathogen was not detected in orchard trees during either the dormant or fruit-bearing stages. Conclusions: Thus, obtained results demonstrate an ecological and epidemiological specificity of 'Ca. P. solani' for certain host species, characterized by a high incidence in Solanaceae, particularly tomato. Additionally, the study confirms the potential role of ruderal species within the same family as natural reservoirs of the pathogen. These data contribute to a deeper understanding of the spread of the phytoplasma providing a base for effective monitoring and phytosanitary management strategies.

Citrus huanglongbing (HLB), caused by ‘Candidatus Liberibacter asiaticus’ (CLas), is a destructive disease threatening global citrus industry. Although citrus cultivars differ in HLB sensitivity, how infection alters endophytic bacterial communities in cultivars with contrasting susceptibility remains unclear. Here, we compared endophytic microbiome shifts in leaf and root tissues of HLB-susceptible Shatangju mandarin (Citrus reticulata cv. Shatangju) and HLB-tolerant Shatian pomelo (C. maxima cv. Shatian) at 10 months postgrafting with CLas-infected buds. Infected Shatangju mandarin showed severe symptoms and higher CLas levels in leaves than in roots, while infected Shatian pomelo remained asymptomatic with higher CLas in roots than in leaves. High-throughput 16S rRNA gene sequencing revealed that CLas infection restructured the endophytic microbial community in a tissue-specific manner. CLas-infected Shatian pomelo leaves displayed increased microbial diversity and network complexity, while CLas-infected Shatangju mandarin roots harbored more disease-suppressive taxa like Streptomyces. Across both cultivars, network complexity correlated inversely with CLas abundance. Key genera (e.g., Pseudomonas, Streptomyces, and Prevotella) correlated positively with CLas, suggesting roles in mitigating pathogen effects. Predicted functional profiling indicated activated pathways (amino acid metabolism, terpenoid/polyketide biosynthesis, and xenobiotic biodegradation) potentially supporting host defense in infected tissues. The HLB tolerance of Shatian pomelo appeared linked to tissue-specific bacterial restructuring, particularly recruitment of antibiotic-producing bacteria and enhanced metabolic resilience. These findings elucidated cultivar-specific microbial strategies against CLas, offering insights for microbiome-mediated HLB management.