Bacterial leaf symbiosis in Ardisia (Myrsinoideae, Primulaceae): molecular evidence for host specificity.

The association between bacteria and leaves in Ardisia has been described as a cyclic and obligate symbiosis in which bacteria are maintained throughout all stages of the plant's life cycle to guarantee normal growth and survival of the host. This intimate interaction suggests that both partners have co-diversified together. To test this co-speciation hypothesis, we constructed an endosymbiont (16S rDNA and gyrB) and host (rps16, trnL, matK and ITS) phylogeny. Phylogenetic analyses of the endosymbionts revealed a pattern of strict host specificity and recovered a single clade in the genus Burkholderia (β-proteobacteria), which was closely related to the endosymbionts of leaf-nodulated Rubiaceae. Comparison of symbiont and host phylogenies suggests a single origin of bacterial leaf symbiosis in the nodulated ancestor of Ardisia and does not reject the co-speciation hypothesis.