Abstract
Background Spiroplasma citri is a wall-less bacterium that colonizes phloem vessels of a large number of host plants. Leafhopper vectors transmit S. citri in a propagative and circulative manner, involving colonization and multiplication of bacteria in various insect organs. Previously we reported that phosphoglycerate kinase (PGK), the well-known glycolytic enzyme, bound to leafhopper actin and was unexpectedly implicated in the internalization process of S. citri into Circulifer haematoceps cells.Methodology/Principal FindingsIn an attempt to identify the actin-interacting regions of PGK, several overlapping PGK truncations were generated. Binding assays, using the truncations as probes on insect protein blots, revealed that the actin-binding region of PGK was located on the truncated peptide designated PGK-FL5 containing amino acids 49–154. To investigate the role of PGK-FL5-actin interaction, competitive spiroplasma attachment and internalization assays, in which His6-tagged PGK-FL5 was added to Ciha-1 cells prior to infection with S. citri, were performed. No effect on the efficiency of attachment of S. citri to leafhopper cells was observed while internalization was drastically reduced. The in vivo effect of PGK-FL5 was confirmed by competitive experimental transmission assays as injection of PGK-FL5 into S. citri infected leafhoppers significantly affected spiroplasmal transmission.ConclusionThese results suggest that S. citri transmission by its insect vector is correlated to PGK ability to bind actin.
Highlights
The plant pathogenic mollicute Spiroplasma citri, available in culture since 1971 [1,2], has emerged as an outstanding model for studying spiroplasma interactions with its two experimental hosts: the periwinkle plant and the insect vector Circulifer haematoceps [3]
These results suggest that S. citri transmission by its insect vector is correlated to phosphoglycerate kinase (PGK) ability to bind actin
For S. citri, we previously reported that phosphoglycerate kinase (PGK), a key enzyme in glycolysis which is classified as a cytosolic protein, unexpectedly bound actin and mediated the process leading to internalization of S. citri in eukaryotic cells [16]
Summary
The plant pathogenic mollicute Spiroplasma citri, available in culture since 1971 [1,2], has emerged as an outstanding model for studying spiroplasma interactions with its two experimental hosts: the periwinkle plant and the insect vector Circulifer haematoceps [3]. Successful transmission of S. citri by the leafhopper depends mainly on the ability of spiroplasmas to pass through the insect gut cells, to multiply in various tissues, and to cross the salivary gland cells. The crossing of these different barriers doubtlessly requires protein interactions between the spiroplasma cells and cells of its insect host. We reported that phosphoglycerate kinase (PGK), the well-known glycolytic enzyme, bound to leafhopper actin and was unexpectedly implicated in the internalization process of S. citri into Circulifer haematoceps cells
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