TAXONOMIC STATUS OF THE AGENT OF CEREALS PALE-GREEN DWARF AND PROPOSITION OF FOUNDING IN THE CLASS OF MOLLICUTES, OF THE ORDER III ACHOLEPLASMATALES, FAMILY I ACHOLEPLASMATACEAE, GENUS II PLURAPLASMA GEN. NOV., AND ITS FIRST SPECIES

He data are presented on taxonomic status of the agent of cereals pale-green dwarf (ACPGD) which has been defined as the phytopathogenic variant of the mollicute Acholeplasma laidlawii and called A. laidlawii var. granulum. Phytopathogenicity of ACPGD possess several fundamental differences from A. Laidlawii as: large genome consisting of 2,200 thousand pairs of nucleotides (t.p.n.) to 2,310 t.p.n. that practically equals a sum of genomes of A. Laidlawii (1,600 t.p.n.) and phytoplasmas (710 t.p.n.); two forms of DNA-dependent RNA-polymerase (only form functions in A. laidlawii); capacity to form extracellular fructosobisphosphatase that looks like its hypothetical phylogenetic precursor on bacteria Bacillus subtilis; availability of numerous enzymatic activities that are absent in acholeplasmas; peculiar relation to sterols availability in nutrient media that is not characteristic for the known acholeplasmas; extremely rich, as to quantity and quality, composition of antigens capable of reacting almost homologously with antibodies against representatives of Acholeplasma genus and separate species of Mycoplasma genus; great similarity (above 88 %) of sequences of 16S rRNA of ACPGD and representatives of Phytoplasma genus; other properties. It is concluded, that taking into account its characteristics, ACPGD cannot be referred to either of existing genera of the Mollicutes class, since according to its features, this mollicute is a transition form of the microorganism. It is the hitherto an unknown chain between these genera of mollicutes and sporiferous bacteria. ACPGD can be representative of mollicute precursor with genome of about 1,600 t.p.n. and of genera Acholeplasma and Phytoplasma that arised as a result of evolutionary splitting of their genome. Thus, it is recommended to include ACPGD in the Mollicutes class, order III Acholeplasmatales, family I Acholeplasmataceae as a new genus II Pluraplasma gen. nov., and its first species Pluraplasma granulum sp. nov, strain 118, being its typical representative.