Immunodominant membrane proteins from two phytoplasmas in the aster yellows clade (chlorante aster yellows and clover phyllody) are highly divergent in the major hydrophilic region.

The mechanisms by which phytoplasmas interact with their hosts are not understood. Mollicute membrane proteins may play a role in such interactions and therefore the amp genes encoding immunodominant proteins from two phytoplasmas, aster yellows and clover phyllody, which fall within the largest taxonomic subclade of the phytoplasmas, have been cloned and characterized. The putative translation products, antigenic membrane proteins (Amps), of these genes have properties which are typical for bacterial membrane proteins, and which suggest that each has a single large extracellular hydrophilic domain held by a transmembrane region near the C-terminus, with only a short C-terminal intracellular sequence.

An immunodominant membrane protein gene from the Western X-disease phytoplasma is distinct from those of other phytoplasmas.

Membrane proteins mediate several important processes, including attachment, in several Mollicute species. Phytoplasmas are non-culturable plant pathogenic mollicutes that are transmitted in a specific manner by certain phloem-feeding insect vectors. Because it is likely that phytoplasma membrane proteins are involved with some aspect of the transmission process, their identification, isolation and characterization are important first steps in understanding phytoplasma transmission.

Isolation of the gene encoding an immunodominant membrane protein of the apple proliferation phytoplasma, and expression and characterization of the gene product.

An immunodominant membrane protein (IMP) of the apple proliferation (AP) phytoplasma was detected in preparations from AP-diseased periwinkle plants using monoclonal and polyclonal antibodies to the AP agent. Following isolation from Western blots and partial sequencing, degenerate oligonucleotides derived from the IMP sequence were used as probes to identify a DNA fragment containing the ORF encoding the IMP. Complete sequencing and subsequent analysis of the cloned DNA fragment revealed the presence of two ORFs, predicted to encode proteins with molecular masses of 25 kDa (P-318A) and 19 kDa (P-318B).