Publications

4947

Abstract Phytoplasma diseases are threat to sesame and its wild relatives, but information on their occurrence in exotic Sesamum species is limited. During field evaluation, Sesamum angolense , S. angustifolium , and S. latifolium exhibited characteristic phyllody and witches' broom symptoms, including virescence, leafy floral organs, polysepalous calyx, polypetalous corolla, flattened stamens, shortened internodes, excessive shoot proliferation, and leaf twisting and curling. Molecular detection using universal phytoplasma primers P1/P7 and tuf gene-specific primers fTufAy/rTufAy amplified products of approximately 1.8 kb and 940 bp, respectively, from symptomatic plants. Sequence analysis of the 16S rRNA and tuf genes revealed 99–100% nucleotide identity with members of the 'Candidatus Phytoplasma asteris ' group. Phylogenetic reconstruction based on both loci consistently assigned the isolates to the 16SrI-B subgroup of 'Ca. Phytoplasma asteris'. To the best of our knowledge, this is the first report of phytoplasma infection in S. angolense , S. angustifolium , and S. latifolium , characterized at the strain level using both 16S rRNA and tuf gene sequences. The findings expand the known host range of 16SrI-B phytoplasmas and demonstrate that these wild Sesamum species, which are valuable components of the tertiary gene pool of cultivated sesame, can serve as natural reservoirs of phytoplasma inoculum.

Abstract Huanglongbing (HLB), primarily induced by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas), poses a significant threaten to citrus production worldwide. CLas deploys Sec-dependent effectors (SDEs) to manipulate host cellular processes, yet the underlying virulence mechanisms remain incompletely understood. Here, we identify SDE4580, a conserved CLas effector localized to the plant plasma membrane, as a key virulence factor that promotes pathogen proliferation and suppresses host immunity across citrus and Arabidopsis. Transcriptomic analysis reveals that SDE4580 reprograms membrane-associated biological processes and defense responses. Through yeast two-hybrid screening and biochemical validation, we demonstrate that SDE4580 physically interacts with the citrus vesicle trafficking regulator CsPRA1.E, a Prenylated Rab Acceptor 1 family protein. Functional assays establish CsPRA1.E as a positive regulator of immunity that promotes apoplastic secretion of defense-related proteins and enhances resistance to Xanthomonas citri subsp. citri. Crucially, SDE4580 antagonizes CsPRA1.E-mediated resistance by suppressing defense protein secretion without inducing target degradation. These findings uncover a novel pathogenic strategy whereby CLas subverts host endomembrane trafficking to disarm plant immunity. Targeting the SDE4580-CsPRA1.E interface may offer a promising avenue for developing durable HLB control strategies.

The spread of the reed planthopper Pentastiridius leporinus and its associated pathogens Candidatus Arsenophonus phytopathogenicus (ARSEPH) and Candidatus Phytoplasma solani (PHYPSO) increasingly threatens sugar beet production in Central Europe. Current surveillance systems rely mainly on vector monitoring, visual field assessments and molecular diagnostics of individual vectors and plants, all of which provide valuable but spatially limited information. This study evaluated sugar beet pulp samples generated during routine factory quality assessment as a large- scale surveillance resource for PHYPSO. During the 2025/26 campaign, 4887 pulp samples representing 1954 delivery field locations were collected, of which 1237 samples of individual field locations with consistent beet quality parameters were analyzed by direct PCR. PHYPSO was detected in 214 samples (17.3%). The molecular workflow was not subgroup-specific and did not include genotyping; therefore, PHYPSO-positive samples could not be assigned to individual 16SrXII subgroups. Comparison with visual field assessments showed that 85.7% of positive molecular detections originated from fields without visible symptoms. A carry-over experiment demonstrated that pathogen-derived DNA may persist across consecutive samples under worst-case conditions and must therefore be considered during data interpretation. In contrast, ARSEPH was detected by direct PCR in only six of 1237 samples (0.5%), all originating from the Euskirchen growing region. Comparison with qPCR, single-beet diagnostics and the carry-over experiment indicated insufficient sensitivity of the current ARSEPH direct-PCR assay; therefore, the observed detection rate should not be interpreted as true pathogen prevalence. Nevertheless, the observed spatial distribution patterns of monitoring sites indicate that industrial pulp sample monitoring substantially expands surveillance coverage beyond conventional symptom-based approaches and can help identify regions warranting further epidemiological investigation.

Peptidyl-tRNA hydrolase (Pth2) hydrolyzes peptidyl-tRNA, an immature product of aborted translation, into peptide and tRNA, thereby maintaining cellular protein synthesis through peptide release and tRNA recycling. Here, we present the crystal structure of Pth2 from Candidatus Lokiarchaeum sp. GC14_75 ( Loki Pth2) at 2.12 Å resolution. This is the first structure of Pth2 from a lineage within Promethearchaeati, a kingdom of archaea closely related to eukaryotes. The structure reveals that Loki Pth2 forms a homodimer and closely resembles Pth2 structures from other species. However, Loki Pth2 exhibits two prominent structural differences: a short helix around the catalytic center, which is absent in other Pth2s, and a distinct orientation of the C-terminal helix. Detailed comparative structural analysis suggests that these regions may regulate enzymatic activity and substrate binding, respectively. Furthermore, the corresponding regions in other Pth2s also exhibit high flexibility, suggesting that similar mechanisms may be conserved among Pth2s. To gain insights into the growth environment of Candidatus Lokiarchaeum sp. GC14_75, we assess the optimal temperature for the catalytic reaction of Loki Pth2, which suggests that Candidatus Lokiarchaeum sp. GC14_75 inhabits moderately thermophilic environments.