Yang, Kun

Background: The Asian Haemaphysalis longicornis is capable of transmitting a wide range of zoonotic pathogens. This study aimed to investigate the prevalence and characteristics of major pathogens in questing H. longicornis ticks collected from two geographically and ecologically distinct regions in China. Methods: A total of 1004 questing H. longicornis ticks were collected from Liaoning Province (Northeast China; n = 882) and Anhui Province (Central and Eastern China; n = 122) and pooled into 670 mixed samples. Tick species were identified by mitochondrial cytochrome oxidase I gene sequencing. Nucleic acid samples from all pools were first screened for Dabie bandavirus using RT-PCR and for bacteria using universal 16S rRNA primers. Bacteria-positive samples were further tested using polygenic seminested PCR for Rickettsia spp. and Coxiella -like endosymbionts (CLEs). Phylogenetic analyses, including polygene sequence analysis, were performed to ensure the accuracy of species identification and to explore genetic relationships. Results: No Dabie bandavirus was detected in any samples. Among the 670 tick pools, 14 were positive for spotted fever group rickettsiae (SFGR), with an overall minimum infection rate (MIR) of 1.4% (14/1004). Notably, the detected SFGR species showed clear geographic segregation: Candidatus Rickettsia jingxinensis was detected only in Liaoning Province (MIR of 1.4%), while Rickettsia heilongjiangensis was found exclusively in Anhui Province (MIR of 1.6%). Additionally, CLEs (overall MIR of 2.0%) were identified in 20 tick pools, with a significantly higher prevalence in Anhui Province (10.7%) than in Liaoning Province (0.8%; p < 0.001). Conclusions: This surveillance revealed a distinct geographical distribution pattern of SFGR species in H. longicornis populations in China and confirmed the presence of Ca . R. jingxinensis in the northeast and R. heilongjiangensis in the central and eastern regions. These findings, supported by polygenic evidence, provide essential epidemiological data for understanding regional tick-borne disease risks and highlight the need for continued region-specific surveillance.

ABSTRACT Citrus huanglongbing (HLB), caused by “ Candidatus Liberibacter” spp., is one of the most disastrous citrus diseases worldwide. HLB‐affected citrus fruits are significantly more acidic than healthy fruits. However, the molecular mechanism behind this phenomenon remains to be elucidated. Here, we report that HLB‐affected fruits have higher levels of citric acid (CA) than healthy fruits. Moreover, Citrus PH4 ( CitPH4 ), which encodes a MYB transcription factor that functions as a key regulator of CA accumulation, was upregulated in HLB‐affected fruits relative to healthy fruits. Heterologous overexpression of CitPH4 in tobacco ( Nicotiana tabacum ) plants enhanced tolerance to HLB. Subsequently, overexpression and gene‐editing experiments indicated that CitPH4 can affect the salicylic acid (SA) pathway, which directly binds to and activates the promoter of CsPBS3 , a key gene of SA biosynthesis. HLB‐affected fruits had higher SA levels than healthy fruits. Furthermore, application of SA activated CA biosynthesis and application of CA activated SA biosynthesis and signalling in citrus fruits and decreased “ Candidatus Liberibacter asiaticus” ( C Las) titres in infected leaves. This work suggests that CitPH4 is a key node between CA and SA, thus revealing crosstalk between defence responses and fruit quality in citrus.