The AAA+ ATPases and HflB/FtsH Proteases of ‘Candidatus Phytoplasma mali’: Phylogenetic Diversity, Membrane Topology, and Relationship to Strain Virulence

摘要

Previous examination revealed a correlation of phytopathogenicuddata of ‘Candidatus Phytoplasma mali’ strains andudthe DNA sequence variability of a type ATP00464 hflBudgene fragment. To further investigate such a relationship,udall distinct genes previously annotated as hflB in the genomeudof ‘Ca. P. mali’ strain AT were fully sequenced and analyzedudfrom a number of representative mild, moderate, and severeudstrains. The re-annotation indicated that the sequencesudencode six AAA+ ATPases and six HflB proteases. Each ofudthe nine distinct deduced AAA+ proteins that were examinedudformed a coherent phylogenetic cluster. However,udwithin these groups, sequences of three ATPases and threeudproteases from mild and severe strains clustered distantly,udaccording to their virulence. This grouping was supportedudby an association with virulence-related amino acid substitutions.udAnother finding was that full-length genes fromudATPase AP11 could only be identified in mild and moderateudstrains. Prediction of the membrane topology indicatedudthat the long ATPase- and protease-carrying C-terminaludtails of approximately half of the AAA+ proteins are extracellular,udputatively facing the environment of the sieve tubes.udThus, they may be involved in pathogen–host interactionsudand may compromise phloem function, a major effect ofudphytoplasma infection. All full-length genes examinedudappear transcriptionally active and all deduced peptidesudshow the key positions indicative for protein function.