Hemolysin-like Protein of 'Candidatus Phytoplasma Mali' Is an NTPase and Binds Arabidopsis thaliana Toc33.

'Candidatus Phytoplasma mali' is associated with apple proliferation, a devastating disease in fruit production. Using genome analysis, a gene encoding a hemolysin-like protein was identified. It was postulated that this protein could be an effector. However, the function of this protein is unknown. It is shown that the hemolysin-like protein binds to a GTP binding protein, Toc33, of Arabidopsis thaliana in yeast two-hybrid analysis and that the Toc33-binding domain is located in the C-terminus of the domain of unknown function (DUF21) of the protein. The biochemical studies reveal that the protein can hydrolyze phosphate of purine and pyrimidine nucleotides. Transgenic Nicotiana benthamiana plants expressing the protein show no discernible change in phenotype. Phytoplasma have a much-reduced genome, lacking important genes for catabolic pathways or nucleotide production; therefore, the hemolysin-like protein plays a role in the uptake of plant nucleotides from their host and hydrolyzes these nucleotides for energy and their own biosynthesis.