Publications

4888

ABSTRACT Insect‐vectored pathogens pose a significant threat to global agriculture. The colonization efficiency of pathogens in vectors plays a central role in these pathosystems, yet studies of the factors that affect this aspect are limited. This study investigates the genetic and microbial symbiont factors influencing the susceptibility of Diaphorina citri to Candidatus Liberibacter asiaticus ( C Las), the pathogen causing citrus greening disease (huanglongbing). Through a microbiome Genome Wide Association Study (mGWAS) based on 16S amplicon sequencing and genomic resequencing of 120 D. citri individuals from six populations, we identified 79 SNPs significantly associated with the relative abundance of C Las within insects. Additionally, some of these SNPs were also associated with the relative abundance of Candidatus Profftella armature, a key endosymbiont of D. citri . SNPs in the regulatory region of gene Dcitr04g11610.1 led to its overexpression in C Las‐susceptible D. citri , and C Las infection further elevated its expression. Conversely, RNAi knockdown of Dcitr04g11610.1 reduced C Las infection rates and abundance, accompanied by increased abundance of Profftella . Phylogenetic analysis revealed Dcitr04g11610.1 ’s high homology to Major Facilitator Superfamily‐type transporter SLC18B1 proteins, suggesting a role in C Las polyamine utilization. These findings highlight the importance and potential interplay of insect genetics and symbiotic microbiota in insect‐vectored plant pathogen systems.

ABSTRACT Citrus huanglongbing (HLB), caused by the phloem‐limited bacterium ‘ Candidatus Liberibacter asiaticus’ ( C Las), is one of the most destructive diseases in global citrus production. Here, we report the functional characterization of a core C Las effector, CLIBASIA_00525 named SDE525, that manipulates host immunity by targeting the citrus nascent polypeptide‐associated complex alpha subunit (CsNACα). We confirmed that SDE525 is a secreted protein that localizes to the nucleus, cytoplasm, and plasma membrane. Notably, the effect of SDE525 exhibits host‐specific context dependence: while its transient expression in the non‐host Nicotiana benthamiana unexpectedly triggered immune responses, in its native host, sweet orange ( Citrus sinensis ), SDE525 interacted with CsNACα to modulate defence, as demonstrated by multiple independent assays. Integrated transcriptomic and metabolomic analyses revealed that this interaction reprograms the host's hormonal landscape, suppressing the jasmonic acid (JA) signalling pathway while simultaneously activating the salicylic acid (SA) pathway. Importantly, under transient overexpression conditions in citrus, this immune reprogramming enhanced resistance against the bacterial canker pathogen Xanthomonas citri subsp. citri —a phenomenon distinct from the susceptibility observed during authentic C Las infection. Our findings uncover a sophisticated mechanism by which a C Las effector rewires host defence signalling, providing fundamental insights into its pathogenesis with potential long‐term implications for future HLB management.

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), 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.

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.

ABSTRACT Background Data on feline hemotropic mycoplasmas is limited in Iran. Aim. The aim of this study was to investigate the infection rate of cats with this pathogen in Mashhad,Iran and evaluate its assosiation with cliniopathological changes. Materias & Methods Blood samples from 100 cats presenting at veterinary clinics were analysed for Mycoplasma haemofelis (Mhf) and Candidatus Mycoplasma haemominutum (CMhm). Samples were screened for hemotropic mycoplasmas using microscopic examination and conventional polymerase chain reaction (PCR). Samples were also subjected to haematological and biochemical analysis. Results Microscopic examination detected hemotropic mycoplasmas in 65% of samples, whereas PCR identified a 23% infection rate, with 65.21% ( n  = 15) positive for CMhm and 34.78% ( n  = 8) for Mhf. The presence of Haemomycoplasma DNA was significantly associated with age, gender, breed and roaming status ( p  < 0.05). Infected cats exhibited significant alterations ( p  < 0.05) in haematocrit (Hct), red blood cell count (RBC), haemoglobin (HGB), white blood cell count (WBC), neutrophil counts, serum total protein (TP), globulin, phosphorus (Pi), aspartate aminotransferase (AST) levels and the albumin/globulin ratio (AGR). Conclusions Our study highlights a high prevalence of feline hemoplasmosis in northeastern Iran, with CMhm as the predominant species. Key risk factors included male gender, adult, outdoor access and domestic short hair (DSH) breed. Although infected cats showed consistent clinicopathologic changes, no differences were observed between Mhf and CMhm infections.