Identification and evolutionary analysis of putative cytoplasmic mcpA-like protein in a bacterial strain living in symbiosis with a mycorrhizal fungus

In this paper we report the identification and characterization of a DNA region containing putative mcpA-like gene coding for a Methyl Accepting Chemotaxis Protein (MCP) and belonging to a Burkholderia endosymbiont of the arbuscular mycorrhizal fungus Gigaspora margarita. A genomic library of total DNA extracted from the fungal spores, representative of the bacterial genome, was used to investigate the prokaryotic genome. PCR experiments with primers designed on the Burkholderia mcpA-like gene and Southern blot analysis demonstrate that they actually belong to the genome of G. margarita endosymbiont. The expression of the mcpA-like gene in the fungal spores was demonstrated by RT-PCR experiments. The detailed comparative analysis of the bacterial MCPs available in databases allowed to draw a possible evolutionary pathway leading to the present-day mcpA genes. Accordingly, the ancestor of the mcpA-like genes was the result of a domain shuffling event involving two ancestral mini-genes encoding a PAS-PAC and a MA domains, respectively, followed by the elongation of the PAS-PAC moiety. The following evolutionary divergence involved not only point mutations, but also larger rearrangements (insertions and deletions) at the 3′ end of the gene.