Publications

4369

From 2016, witches’ broom and stunting symptoms were observed in Lolium rigidum grown in some fruit tree nurseries in Faragheh (Abarkouh, Yazd province, Iran). Total DNAs were extracted from symptomatic and asymptomatic plants and assessed for phytoplasma presence using direct and nested PCR to detect the 16S ribosomal RNA gene. From all symptomatic L. rigidum plant samples, expected length PCR amplicons were obtained. RFLP analysis with informative restriction enzymes showed identical profiles in all the samples resulted positive, that were also consistent with those of one of the subgroups of the aster yellows phytoplasmas (16SrI). The 16S rRNA gene sequence of Faragheh L. rigidum bushy stunt strain was 100% identical to some ‘Candidatus Phytoplasma asteris’ related strains, and 99.12% similar to the reference ‘Ca. P. asteris’ strain. The virtual RFLP pattern was identical (similarity coefficient 1.00) to the pattern of phytoplasmas in subgroup 16SrI-F. This is the first report of occurrence and molecular identification of this phytoplasma strain in L. rigidum and indicates a potential phytoplasma reservoir for trees in fruit tree nurseries where insect vectors may be present. This phytoplasma strain has been reported in symptomatic stone fruits in Spain and in potato in Ecuador. Further research on the epidemiology of witches’ broom and stunting in L. rigidum is required to develop elimination the phytoplasma from areas surrounding agricultural crops and avoid the risks of epidemics.

Abstract Rickettsia species, which constitute obligate intracellular bacteria adapted to a host-dependent lifestyle, have traditionally been classified into four phylogenetic groups. However, the available genomes are biased toward the Typhus and Spotted Fever groups, with early-diverging Ancestral group (AG) lineages being underrepresented. Here, we isolated six Candidatus Rickettsia mendelii strains from Ixodes turdus ticks in Japan. We obtained their whole-genome sequences, including one closed genome, and found that they form a distinct lineage in the AG and have the smallest genome among the known rickettsial species. Gene tree-aware reconstruction of evolutionary events using amalgamated likelihood estimation revealed that the last common ancestor of Rickettsia had a smaller gene family size than modern species do, and Ca . R. mendelii retains the most similar genomic content to this ancestral state. Various patterns of gene gain and loss among Rickettsia lineages were also suggested, highlighting their divergent evolutionary trajectories. These findings increase our understanding of Rickettsia genome evolution.