Publications

4481

Brinjal little leaf (BLL) disease, caused by phytoplasmas, leads to significant yield losses, but its pathogenic mechanisms remain poorly understood. This study characterizes SAP54LP/S54LP (SAP54-like protein of BLL), an effector protein associated with the 16SrVI-D phytoplasma strain linked to BLL in Tamil Nadu, India. Molecular analyses, including nested PCR and virtual RFLP, confirmed the phytoplasma's classification within the 16SrVI group. The S54LP effector gene was amplified from infected brinjal, confirming its presence. Sequence comparisons showed that S54LP was 100 % identical to homologs in the 16SrVI-A group and 98 % identical to those in the 16SrIB group (phyl1 and S54LP), indicating group-specific divergence. Comparative analysis identified 13 single nucleotide polymorphisms (SNPs), 69 % of which led to nonsynonymous substitutions in the mature protein, potentially affecting host interactions. Haplotype network analysis revealed a globally distributed Hap_6 lineage and region-specific haplotypes, suggesting localized evolutionary dynamics. Evolutionary analysis indicated strong purifying selection on the coding sequence (Ka/Ks ≈ 0.3), reflecting the conservation of functional domains essential for pathogenicity. Conversely, positive selection was detected in the signal peptide region, implying adaptive evolution related to secretion and host targeting. Additionally, AT-rich codon usage at specific sites highlights multiple layers of evolutionary constraints shaping S54LP. Overall, these findings establish S54LP as a model for studying host-phytoplasma coevolution, providing insights into effector biology and informing strategies to manage phytoplasma diseases in crops.

Background New tick-borne pathogens are being discovered worldwide, and recognized tick-borne diseases are becoming increasingly diverse. Candidatus R. jingxinensis is endemic in Asia, but its potential to cause clinical infection in humans remains unclear. This study was designed to elucidate the prevalence and delineate the clinical profile of Candidatus Rickettsia jingxinensis infection in Liaoning Province, China. Methods The subjects of this study were suspected cases of tick-borne infectious diseases admitted to the First Affiliated Hospital of China Medical University or reported to the Liaoning Provincial Center for Disease Control and Prevention in 2018–2022. Epidemiological and clinical data were collected. Tick-borne pathogens were detected with a microfluidic chip detection system, and specific gene fragments of the screened pathogens were amplified, sequenced, and compared. Evolutionary and phylogenetic trees were constructed and analyzed. Results In total, 398 infected subjects from 14 cities were included in the study, and 255 tick-borne pathogens were detected. Among these, 11 subjects were found to be infected with Candidatus Rickettsia jingxinensis. This is the first time this strain has been shown to cause infection and illness in humans. The main clinical features of subjects infected with Candidatus R. jingxinensis included fever, fatigue, dizziness, headache, nausea, diarrhea, general pain or muscle and joint pain, reduced leukocytes and platelets, abnormal coagulation function and liver function. Conclusions This study documents the first human infections with Candidatus R. jingxinensis, confirms its prevalence in Liaoning Province, and delineates the primary clinical manifestations of the disease.

Abstract Cable bacteria are filamentous microorganisms capable of centimeter‐scale electron transport, which have great impacts on sediment biogeochemistry, especially oxygen consumption and sulfide depletion. While 16S rRNA sequences related to known cable bacteria have been identified in saline lakes, their genomic diversity, metabolic potentials, and evolution remain unknown. Eight cable bacteria genomes were retrieved from 23 sediment metagenomes across four saline lakes, representing five novel species adapted to different salinity niches. A deep‐branching Electronema species, named Electronema qinghaiense , was found preferentially in brackish to saline environments, implying an ecological and evolutionary link between marine and freshwater lineages. Based on genome analysis, the three newly named cable bacteria species are likely mixotrophic diazotrophs capable of degrading diverse complex carbohydrates, while also participating in hydrogen metabolism via various groups 3 and 4 [NiFe]‐hydrogenases. Genome streamlining and horizontal gene transfer likely drove ecophysiological differentiation among these Electrothrix and Electronema species, including an interphylum horizontal transfer of glycine/sarcosine N‐methyltransferase ( gsmt ) and sarcosine/dimethylglycine N‐methyltransferase ( sdmt ) genes into their common ancestor. Subsequent loss of these genes in some descendants led to adaptation to different salinity niches. Given the inferred ancestral physiological properties, phylogenomic analysis and the evidence that “freshwater” Electronema species experienced stronger purification selection than “saline” Electronema and “hypersaline” Electrothrix species, the evolutionary progression of cable bacteria occurred most likely in the saline‐to‐freshwater direction. Additionally, cable bacteria ecotypes adapted to specific salinity niches likely formed from selective sweeps with low homologous recombination. Collectively, these findings deepen our understanding of the ecophysiology and evolution of cable bacteria.

A Microviridae phage, CLasMV1, was recently identified in ‘ Candidatus Liberibacter asiaticus’ (CLas), the bacterium associated with citrus Huanglongbing (HLB). The CLasMV1 strain GDHZ11D (CP045566) exhibited a circular genome of 8,869 bp containing eight open reading frames (ORFs). Phages of CLas play crucial roles in regulating bacterial population diversity that have potential use for HLB control. However, knowledge of CLasMV1 population diversity is currently limited. In this study, 1,520 CLas samples were collected from 10 citrus-growing provinces in China. PCR screening revealed that 1,042 samples (69%) harbored CLasMV1. Complete genome sequences of 43 CLasMV1 strains were obtained through Illumina HiSeq sequencing with genome sizes ranging from 8,696 to 8,881 bp. Variations were mostly related to single-nucleotide polymorphisms and sequence insertions/deletions. Notably, two hypervariable regions (HVRs) were identified. Two new ORFs were detected, ORF-A (144 bp) in HVR-1 and ORF-B (342 bp) in HVR-2. Whole-genome phylogenetic analysis using 43 strains from this study, 9 previously reported Chinese strains, and 2 Florida strains (CP040636 and MZ382797) delineated five genomic groups. Chinese strains dominated Groups 1 to 4, and Group 5 contained the Florida strains. Further analyses of HVR-1 across all 1,042 CLasMV1 samples detected a 173-bp sequence with suspected mobile activity. Analysis of a PacBio long-read assembly published previously detected a concatemer of the CLasMV1 sequence, suggesting that the phage used the rolling circle mechanism for its replication. These findings significantly enhance our understanding of CLasMV1 genomic diversity and will facilitate future research on CLasMV1 classification and HLB biology.

ABSTRACT Phytoplasmas were detected in potato tubers and sugar beet roots in neighbouring fields in Southern Germany using quantitative PCR. Infected potato plants showed phytoplasma‐associated symptoms including yellowing, upward leaf rolling, aerial tubers and early senescence. Sugar beet plants showed similar symptoms to those of syndrome ‘basses richesses’ (SBR) disease, including proliferation, yellowing and necrosis of older leaves. The genetic diversity of the phytoplasmas in the symptomatic potato and sugar beet plants was investigated through sequence analysis of 16S rRNA and stamp , vmp1 , tuf and secY genes. The RFLP profiles and sequences of 16S rRNA were identical among all the sugar beet‐positive samples and aligned with subgroup 16SrXII‐P, whereas the potato phytoplasma strains were identified as belonging to subgroup 16SrXII‐A. Sequence analysis of the non‐ribosomal genes showed that the potato strains belonged to the b1 group of the tuf gene, the V4 and V17 groups of the vmp1 gene and the secY3 and secY4 groups of the secY gene. However, the sugar beet strain was clearly distinct from the potato strains. Together with strain 916/22 from sugar beet in eastern Germany, they formed a new group of tuf , secY , vmp and stamp genes. RFLP assays and multilocus sequence analysis of non‐ribosomal genes of the phytoplasma strains confirmed that the potato phytoplasma strains were molecularly different from the sugar beet phytoplasma strains. In addition, this is the first report on the multilocus sequence analysis of ‘ Candidatus Phytoplasma solani’ strains in potato plants in Germany, suggesting differences in source plants other than sugar beet or interactions with insect vectors specific to each crop.

‘ Candidatus Liberibacter solanacearum’ (Lso), haplotype D, is an insect-transmitted, phloem-limited bacterium that induces developmental abnormalities in carrots, including witches’ broom and hairy root symptoms. We hypothesize that these symptoms result from Lso-induced hormonal imbalances. To investigate this, we analyzed the spatial and temporal distribution of Lso in carrot plants and assessed its effects on hormone-related gene expression and phytohormone levels. Our findings revealed that Lso first accumulates in the shoot apical meristem before spreading to root tissues, aligning with phloem flow dynamics. Transcriptomic and biochemical analyses indicated that cytokinin (CK) biosynthesis and response genes were upregulated, whereas gibberellin biosynthesis genes were downregulated. In contrast, no significant changes were observed in auxin biosynthesis or signaling. Hormone quantification further demonstrated increased CK levels in lateral roots and decreased CK levels in the root meristem of infected plants, with no detectable changes in auxin levels. Additionally, salicylic acid and jasmonic acid were significantly elevated following Lso infection, suggesting a persistent plant defense response. To validate the role of CK and auxin in symptom development, we applied synthetic growth regulators to infected and uninfected plants. CK treatment exacerbated witches’ broom symptoms, whereas auxin application mitigated this phenotype but enhanced lateral root formation. These results suggest that Lso manipulates phytohormone homeostasis to induce disease symptoms, offering a potential avenue for symptom mitigation through targeted hormone applications. Our findings provide novel insights into the role of plant hormones in Lso pathogenesis and highlight new strategies for managing carrot yellows disease.