Publications

3843

Tobacco (Nicotiana tabacum) is among the agricultural products with the highest added value in Turkey. Although frequently associated with its negative effects on human health, it also provides important contributions to the Turkish economy with the employment it creates in rural areas and continues to be a strategic product. Many postgraduate theses and studies related to the sociological and economic importance of the production of this plant, which is of great importance for our country, have been carried out. However, there are very limited studies on plant diseases in tobacco production areas in Turkey. Phytoplasma is one of the important plant pathogens that cause yield loss in tobacco. Since available data on phytoplasma diseases on tobacco was very scarce worldwide, field surveys to collect samples showing phytoplasma infection-like symptoms such as yellowish color changes, leaf blisters, proliferation, dwarfism, and other physical abnormalities were carried out in Çanakkale and Balıkesir provinces of Turkey from June to August 2021. The presence of phytoplasmas in six samples was confirmed by 16S ribosomal DNA amplification by nested-PCR using universal phytoplasma primer sets, which also suggested the pathogen associated with the symptoms on tobacco. According to phylogenetic study and virtual-RFLP analysis using AluI and MseI endonuclease enzymes, the six Turkish tobacco phytoplasma strains all belong to group 16SrXII and have more than 99% nucleotide sequence identity with some members of ‘Candidatus Phytoplasma solani’ of the taxonomic subgroup ‘stolbur’ (16SrXII-A). Genetic distances analysis indicated that group 16SrI was more closely related to 16SrXII than 16SrVI, in agreement with the groups clustering in the phylogenetic tree. Neutrality tests found that 16SrI and 16SrXII groups are experiencing expanding or bottleneck selections, probably due to new mutations in the 16S rRNA gene fragment. Meanwhile, 16SrVI populations are shown to be undergoing balancing selections, indicating that its isolates have evolved for a long time.

‘Candidatus Phytoplasma solani’ (‘Ca. P. solani’) is a crop pathogen that is a member of the 16SrXII-A ribosomal subgroup. It is also known as stolbur phytoplasma and causes yield losses in several important crops, especially in Solanaceous crops. Different strains of the pathogen are regularly reported all over the world, particularly in the Mediterranean region. In this study, the determination of genetic diversity for the pathogen infecting tomatoes and potatoes was carried out by using multilocus sequence typing analysis for the Tuf, SecY, and Vmp1 genes to gain insight into the epidemiology of ‘Ca. P. solani’ in Turkey. Genetic diversity of the phytoplasmas was investigated by sequence-based phylogenetic analyses and in silico RFLP analysis of related genes. It was determined that all ‘Ca. P. solani’-related strains infecting tomatoes and potatoes were tuf-b, which is linked to field bindweed (Convolvulus arvensis L.). Tomato or potato-infecting ‘Ca. P. solani’-related strains showed similarities with each other; however, the isolates collected from different plants showed genetic differences in terms of the SecY gene. This study indicates that the highest genetic variability of collected samples was found in the Vmp1 gene. RsaI-RFLP analysis of TYPH10F/R amplicons showed that potato-infecting ‘Ca. P. solani’-related strains were found to be similar to some existing V types. However, the V-type of tomato-infecting isolates is not similar to any previously reported V-type. The results indicate that there could be an important genetic diversity of ‘Ca. P. solani’-related phytoplasmas in Turkey. This could indicate various ways in which the pathogen has adapted to the two host plants as a consequence of the various Vmp1 gene rearrangements seen in these two plant hosts. Obtained results also indicate that the epidemiology of ‘Ca. P. solani’-related phytoplasmas in the tomato and potato agroecosystem may be better understood with the use of molecular data on the complex of vmp-types.

Huanglongbing (HLB), the most destructive citrus disease, is associated with unculturable, phloem-limited Candidatus Liberibacter species, mainly Ca. L. asiaticus (Las). Las is transmitted naturally by the insect Diaphorina citri. In a previous study, we determined that the Oceanian citrus relatives Eremocitrus glauca, Microcitrus warburgiana, Microcitrus papuana, and Microcitrus australis and three hybrids among them and Citrus were full-resistant to Las. After 2 years of evaluations, leaves of those seven genotypes remained Las-free even with their susceptible rootstock being infected. However, Las was detected in their stem bark above the scion-rootstock graft union. Aiming to gain an understanding of the full-resistance phenotype, new experiments were carried out with the challenge-inoculated Oceanian citrus genotypes through which we evaluated: (1) Las acquisition by D. citri fed onto them; (2) Las infection in sweet orange plants grafted with bark or budwood from them; (3) Las infection in sweet orange plants top-grafted onto them; (4) Las infection in new shoots from rooted plants of them; and (5) Las infection in new shoots of them after drastic back-pruning. Overall, results showed that insects that fed on plants from the Oceanian citrus genotypes, their canopies, new flushes, and leaves from rooted cuttings evaluated remained quantitative real-time polymerase chain reaction (qPCR)-negative. Moreover, their budwood pieces were unable to infect sweet orange through grafting. Furthermore, sweet orange control leaves resulted infected when insects fed onto them and graft-receptor susceptible plants. Genomic and morphological analysis of the Oceanian genotypes corroborated that E. glauca and M. warburgiana are pure species while our M. australis accession is an M. australis × M. inodora hybrid and M. papuana is probably a M. papuana × M. warburgiana hybrid. E. glauca × C. sinensis hybrid was found coming from a cross between E. glauca and mandarin or tangor. Eremocitrus × Microcitrus hybrid is a complex admixture of M. australasica, M. australis, and E. glauca while the last hybrid is an M. australasica × M. australis admixture. Confirmation of consistent full resistance in these genotypes with proper validation of their genomic parentages is essential to map properly genomic regions for breeding programs aimed to generate new Citrus-like cultivars yielding immunity to HLB.

Abstract The candidate phyla radiation (CPR) has been described as an obligatory group of ultrasmall bacteria associated with host bacteria. They phylogenetically represent a subdivision of bacteria distinct from other living organisms. Using polyphasic approaches, we screened human faecal samples for the detection of Saccharibacteria. The new sequences obtained by sequencing were compared to the complete CPR genomes available to date. Then, we attempted a co-culture of CPR-bacteria and non-CPR bacteria from human faecal samples. We finally aimed to evaluate the prevalence and distribution of these Saccharibacteria sequences in human sources in 16S amplicon datasets. We were able to reconstitute two high-quality Saccharibacteria genomes named Minimicrobia massiliensis and Minimicrobia timonensis. We have established, for the first time in human digestive samples, the coculture of Candidatus Saccharibacteria with two different bacterial hosts. Finally, we showed that 12.8% (610/4,756) of samples sequenced in our laboratory were positive for operational taxonomic units (OTUs) assigned to M.massiliensis. and significantly enriched in human respiratory and oral microbiota. Here, we reported the first genomes and coculture of Saccharibacteria from human gut specimens. This study opens a new field, particularly in the study of the involvement of CPR in the human intestinal microbiota.

“Candidatus Liberibacter asiaticus” (CLas) is the causal agent of citrus Huanglongbing (HLB, also called citrus greening disease), a highly destructive disease threatening citrus production worldwide. A novel Microviridae phage (named CLasMV1) has been found to infect CLas, providing a potential therapeutic strategy for CLas/HLB control. However, little is known about the CLasMV1 biology. In this study, we analyzed the population dynamics of CLasMV1 between the insect vector of CLas, the Asian citrus psyllid (ACP, Diaphorina citri Kuwayama) and the holoparasitic dodder plant (Cuscuta campestris Yunck.); both acquired CLasMV1-infected CLas from an HLB citrus. All CLas-positive dodder samples were CLasMV1-positive, whereas only 32% of CLas-positive ACP samples were identified as CLasMV1-positive. Quantitative analyses showed a similar distribution pattern of CLasMV1 phage and CLas among eight citrus cultivars by presenting at highest abundance in the fruit pith and/or the center axis of the fruit. Transcriptome analyses revealed the possible lytic activity of CLasMV1 on CLas in fruit pith as evidenced by high-level expressions of CLasMV1 genes, and CLas genes related to cell wall biogenesis and remodeling to maintain the CLas cell envelope integrity. The up-regulation of CLas genes were involved in restriction–modification system that could involve possible phage resistance for CLas during CLasMV1 infection. In addition, the regulation of CLas genes involved in cell surface components and Sec pathway by CLasMV1 phage could be beneficial for phage infection. This study expanded our knowledge of CLasMV1 phage that will benefit further CLas phage research and HLB control.