Uncontrolled proliferation is the hallmark of cancer and other proliferative disorders and abnormal cell cycle regulation is, therefore, common in these diseases. Cyclin-dependent kinases (CDKs) play a crucial role in the control of the cell cycle and proliferation. These kinases are frequently deregulated in various cancers, viral infections, neurodegenerative diseases, ischemia and some proliferative disorders. This led to a rigorous pursuit for small-molecule CDK inhibitors for therapeutic uses. Early efforts to block CDKs with nonselective CDK inhibitors led to little specificity and efficacy but apparent toxicity, but the recent advance of selective CDK inhibitors allowed the first successful efforts to target these kinases for the therapies of several diseases. Major ongoing efforts are to develop CDK inhibitors as monotherapies and rational combinations with chemotherapy and other targeted drugs.

Symptoms of general stunting and yellowing of leaves were observed in diseased cultivated strawberry (Fragaria×ananassa Duchesne) in Lithuania. Analysis of 16S rRNA gene sequences amplified by PCR indicated that the symptoms were associated with infection by a phytoplasma, designated strawberry yellows (StrawY) phytoplasma. Phylogenetic analysis of 16S rRNA gene sequences indicated that StrawY phytoplasma, ‘Candidatus Phytoplasma australiense’, ‘Candidatus Phytoplasma asteris’, stolbur phytoplasma and ‘Candidatus Phytoplasma japonicum’ shared a common ancestor, but were mutually distinct. Nucleotide sequence alignments of a 1·3 kb 16S rRNA gene sequence fragment revealed that StrawY phytoplasma shared 97·4 % or less similarity with previously described ‘Candidatus Phytoplasma’ species. These results, in addition to natural host and geographical occurrence, support the recognition of StrawY phytoplasma as a representative of a novel taxon, ‘Candidatus Phytoplasma fragariae’.

Phytoplasmas are classified into 16Sr groups and subgroups and ‘Candidatus Phytoplasma ’ species, largely or entirely based on analysis of 16S rRNA gene sequences. Yet, distinctions among closely related ‘Ca. Phytoplasma ’ species and strains based on 16S rRNA genes alone have limitations imposed by the high degree of rRNA nucleotide sequence conservation across diverse phytoplasma lineages and by the presence in a phytoplasma genome of two, sometimes sequence-heterogeneous, copies of the 16S rRNA gene. Since the DNA-dependent RNA polymerase (DpRp) β-subunit gene (rpoB) exists as a single copy in the phytoplasma genome, we explored the use of rpoB for phytoplasma classification and phylogenetic analysis. We sequenced a clover phyllody (CPh) phytoplasma genetic locus containing ribosomal protein genes, a complete rpoB gene and a partial rpoC gene encoding the β′-subunit of DpRp. Primers and reaction conditions were designed for PCR-mediated amplification of rpoB gene fragments from diverse phytoplasmas. The rpoB gene sequences from phytoplasmas classified in groups 16SrI, 16SrII, 16SrIII, 16SrX and 16SrXII were subjected to sequence similarity and phylogenetic analyses. The rpoB gene sequences were more variable than 16S rRNA gene sequences, more clearly distinguishing among phytoplasma lineages. Phylogenetic trees based on 16S rRNA and rpoB gene sequences had similar topologies, and branch lengths in the rpoB tree facilitated distinctions among closely related phytoplasmas. Virtual RFLP analysis of rpoB gene sequences also improved distinctions among closely related lineages. The results indicate that the rpoB gene provides a useful additional marker for phytoplasma classification that should facilitate studies of disease aetiology and epidemiology.

Although mainly known as pathogens that affect angiosperms, phytoplasmas have recently been detected in diseased coniferous plants. In 2008–2014, we observed, in the Curonian Spit of Western Lithuania and in forests of Southern Lithuania (Varena district), diseased trees of Scots pine (Pinus sylvestris) and mountain pine (Pinus mugo) with unusual symptoms similar to those caused by phytoplasmas. Diseased trees exhibited excessive branching, dwarfed reddish or yellow needles, dried shoots and ball-like structures. restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis of 16S rRNA gene fragments revealed that individual trees were infected by Candidatus (Ca.) Phytoplasma pini-related strains (members of phytoplasma subgroup 16SrXXI-A) or by Ca. Phytoplasma asteris-related strains (subgroup 16SrI-A). Of the nearly 300 trees that were sampled, 80% were infected by phytoplasma. Ninety-eight percent of the positive samples were identified as Ca. Phytoplasma pini-related strains. Strains belonging to subgroup 16SrI-A were identified from only few trees. Use of an additional molecular marker, secA, supported the findings. This study provides evidence of large-scale infection of Pinus by Ca. Phytoplasma pini in Lithuania, and it reveals that this phytoplasma is more widespread geographically than previously appreciated. This is also the first report of phytoplasma subgroup 16SrI-A in pine trees.