Publications

4865

Abstract Background The Toll signaling pathway is a key component of insect innate immunity, yet its role in hemipteran vectors and their interactions with plant pathogens remains poorly understood. The potato psyllid ( Bactericera cockerelli ), an important agricultural pest in the USA, transmits two haplotypes of ‘Candidatus Liberibacter solanacearum ’ (LsoA and LsoB) that cause severe diseases in solanaceous crops. Methods and Results We characterized Toll pathway components in the B. cockerelli genome and examined their transcriptional responses during pathogen acquisition. Six Toll receptors and ten pathway-associated genes were identified in the psyllid genome. Gene expression was evaluated using RT-qPCR following exposure to the entomopathogenic fungus Beauveria bassiana (Bb-490) and infection with Lso haplotypes. The transcription of five Toll receptors was significantly induced in response to B. bassiana , indicating their potential role in antifungal defense. In contrast, Lso infection elicited haplotype-specific transcriptional responses: two Toll receptors (Toll like-1 and Toll-7) were up-regulated during LsoB acquisition, whereas only Toll-7 responded to LsoA. In addition, Spätzle-3 was induced by LsoB, while Spätzle was induced by LsoA. Persistent Lso infection did not significantly alter the transcriptional expression of Toll receptors. Conclusions These findings provide new insights into immune regulation in B. cockerelli and highlight the potential of targeting Toll-mediated responses and fungal biocontrol strategies for sustainable disease management.

Abstract Background ‘ Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited bacterial pathogen causing significant diseases in solanaceous crops. In the United States, haplotypes A and B are transmitted by the potato psyllid Bactericera cockerelli . We previously identified differences in their acquisition and transmission between adults and nymphs. The present study characterized the dynamics of LsoA and LsoB acquisition and transmission by nymphs and examined the transcriptional responses of the nymphal gut upon their acquisition. Methods and results Nymphs were exposed to LsoA- or LsoB-infected plants for 1, 3, 5, or 7 days to measure the bacterial accumulation and for 8 days to assess the transmission efficiency following sequential inoculation of tomato plants. Quantitative PCR showed that LsoB accumulated to higher levels than LsoA after 3 days of acquisition. Following the sequential inoculation, LsoB was transmitted earlier than LsoA indicating a shorter latency period. RNA-seq analysis of the guts following a 1- and 5-day acquisition access periods revealed a greater transcriptional regulation at 5 days than at 1 day. Furthermore, the responses were haplotype-specific: LsoA primarily affected genes involved in protein translation, ER stress, and cell cycle regulation, whereas LsoB regulated genes involved in autophagy, apoptosis, and immune pathways. Conclusions This study revealed haplotype-specific gene regulation potentially leading to LsoB being transmitted more efficiently by psyllid nymphs.

‘ Candidatus Liberibacter asiaticus’ ( C Las) is a phloem-limited bacterium that causes Huanglongbing (HLB), the devastating citrus greening disease that has led to billions of dollars in losses throughout global citrus production. There is very little epidemiological data available regarding fine-scale molecular variability of C Las populations in different regions of the world or their distribution across various geographical landscapes. Here, we present an assessment of C Las genetic diversity using a hypervariable variable number tandem repeat (VNTR) marker (AGACACA) at the CLIBASIA_01645 locus of 344 genomic sequence data obtained from GenBank from five regions of the world (India-177, China-113, Saudi Arabia-37, Bhutan-10, and Nepal-7). The findings revealed high evolutionary plasticity and non-random distribution of TRN within four distinct classes, significantly deviating from a uniform distribution ( p  < 0.05). The analyzed populations were stratified into four distinct classes: Class I (TRN ≤ 5), Class II (TRN > 5 ≤ 10), Class III (TRN > 10 ≤ 15), and Class IV (TRN > 15). The predominant type of subpopulation for all field samples was intermediate variants, with the highest frequencies observed for TRN6 (25%) and TRN7 (17.15%), possibly indicating genomic stability and/or adaptive advantages of specific tandem repeats. On the other hand, lower frequency rare variants (e.g., TRN17, TRN18, and TRN20 at 0.29%) represent some form of continued low frequency micro evolutional replication slippage and corresponding absence of some individual TRs indicates evidence of local purging forces. Crucially, the Indian C Las populations exhibited significantly greater densities of molecular diversity than populations from China, Saudi, Bhutan, and Nepal examined in this study. The distinct TRN signature profiles of these populations’ subpopulations exhibit strong geographic correlation with ecological regions, reinforcing the CLIBASIA_01645 locus as a strong marker for epidemiological surveillance for tracking global strain movement to develop target-specific HLB management programs.

Abstract The evolution of phototrophy and carbon fixation in the phylum Chloroflexota remains incompletely understood, largely due to the scarcity of cultured mesophilic representatives. Here, we report the isolation and genomic characterization of a novel filamentous anoxygenic phototrophic bacterium from a microbial mat in the mesothermal Lake Umkhey (Southern Siberia). Although the original culture was lost, its genome was recovered via metagenome-assembled genome reconstruction from environmental samples, enabling a detailed phylogenomic and metabolic analysis. The genome of umkhey_bin13 (proposed as ‘Candidatus Viridifilum namsaraevi’ gen. nov., sp. nov.) encodes a complete 3-hydroxypropionate bicycle for autotrophic CO₂ fixation, a type II sulfide:quinone oxidoreductase, but lacks nitrogenase and chemolithotrophic markers. Comparative genomics across 18 Chloroflexota genomes reveals that this new lineage occupies an intermediate phylogenetic position, with distinct gene content for sulfur, nitrogen, and hydrogen metabolism, and highlights a complex evolutionary history within the group. Our findings provide new insights into the evolutionary transitions of photosynthetic and carbon-fixation pathways, and underscore the value of integrating cultivation-independent genomics with classical microbiology. The proposed novel genus and species contribute to a revised framework of Chloroflexota evolution and offer a genomic reference for studying metabolic adaptation in alkaline, sulfide-influenced microbial mats.

In Germany, maize (Zea mays L.) is cultivated on approximately 2.4 Mha, making it one of the most widely grown arable crops alongside wheat and barley (German Federal Statistical Office, 2025). Although maize has previously been identified as a host of Candidatus Phytoplasma solani (PHYPSO, 16SrXII-A), particularly in relation to maize redness (MR) disease detected in southeastern Europe (Jović et al., 2009), its role as a host of ‘Candidatus Arsenophonus phytopathogenicus’ (ARSEPH) has not been reported previously. The planthopper Pentastiridius leporinus (Hemiptera: Cixiidae) is the major vector for transmitting both pathogens in many crops in Germany (Rinklef et al., 2024). MR symptoms include patchy premature drying, reddish discoloration of leaves and midribs, poorly filled or aborted ears, and malformed kernels. In August and September 2025, maize plants showing MR-like symptoms were observed in different fields in Otzberg 49°48'25.3"N, 8°52'28.8"E (South Hesse), Bellheim 49°10′19.9N, 8°15′50.8E, Bockenheim 49°36'18.6"N, 8°11'30. E"O, Ibersheim 49°43′36.5″N, 8°24′34.6″E (Rhineland-Palatinate) and Ettling 48°48'50.0"N, 11°40'17.2"E (Baden-Württemberg). Samples from roots (25), leaves (10), ears (14) and kernels (9) of 14 selected symptomatic plants were collected for molecular analysis. DNA was extracted using a CTAB-based protocol. ARSEPH was detected by qPCR targeting the manA gene according to Zübert and Kube (2021). Positive results were obtained from ears of six plants from Ibersheim and Ettling, leaves of three plants from Bockenheim and Otzberg, kernels of two plants from Bellheim, and roots of one plant from Bockenheim. Four ARSEPH-positive samples (two ears and two kernels) were further analyzed using the Fra4/Fra5 PCR assay (Zreik et al. 1998). Sanger sequencing of the resulting amplicons followed by BLAST analysis confirmed all four sequences as ‘Candidatus Arsenophonus phytopathogenicus’ with 100% identity to reference sequence PP400342. The sequences have been deposited in GenBank under accession numbers PZ623476, PZ623478, PZ623483, and PZ626926. Furthermore, all samples were screened for PHYPSO using the qPCR assay described by Behrmann et al. (2022) with primers KL464/KL465. Seven ear samples from Ibersheim yielded positive qPCR signals. To further validate these results, DNA from qPCR-positive samples was subjected to nested PCR targeting the 16S rRNA gene using primer pairs P1/P7 (Schneider et al., 1995) and R16F2n/R16R2 (Gundersen and Lee, 1996), followed by Sanger sequencing and BLAST analysis against the NCBI GenBank database. However, repeated sequencing did not provide sufficient sequence identity to the reference strain STOL11 (GenBank accession number AF248959) to confirm the qPCR-positive samples as PHYPSO. To our knowledge, this is the first report of ARSEPH in maize in Germany. Its detection in maize extends the known host range of this phloem-limited bacterium. The high ARSEPH loads in ears and kernels detected in reproductive tissues are consistent with preferential accumulation in sink organs during grain filling. Whether maize contributes to pathogen persistence and transmission within the Pentastiridius leporinus or other potential vectors’ pathosystem remains to be investigated.

The family Gallionellaceae includes neutrophilic, aerobic, iron-oxidizing bacteria, many of which remain uncultured and known only from metagenomic data. In this study, two high-quality Gallionellaceae genomes were assembled from a ferruginous spring in the Voronezh region, Russia. Phylogenetic analysis based on 120 concatenated proteins, ANI (average nucleotide identity), and AAI (average amino acid identity) indicates that BG-057 belongs to the genus Gallionella and BG-364 to the genus 39-52-133. We propose the names “Candidatus Gallionella aquifuscii” sp. nov. for BG-057 and “Candidatus Dubininella ochracea” gen. nov., sp. nov. for BG-364. Both genomes encode genes for the Calvin-Benson-Bassham (CBB) cycle. Both are potentially capable of aerobic respiration due to the presence of electron transfer chain components. Both genomes encode the iron oxidase Cyc2, and BG-057 also encodes MtoA. BG-057 is potentially capable of lithotrophic growth in the presence of H2 and H2S. BG-364 is potentially capable of growth via Mn (II) oxidation; arsenite oxidation; the direct oxidation of thiosulfate; H2S, elemental sulfur, and sulfite oxidation. BG-364 encodes denitrification genes (narGHI, nirS, norBC). BG-057 possesses systems for the biosynthesis and export of siderophores, while BG-364 lacks these systems but retains Ton-dependent receptors, suggesting the use of exogenous siderophores.