Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2005
Publication Date: 12/14/2005
Citation: Jomantiene, R., Davis, R.E. 2006. Clusters of diverse genes existing as multiple, sequence-variable mosaics in the phytoplasma genome. Federation of European Microbiological Societies Microbiology Letters. 355:59-65.
Interpretive Summary: Phytoplasmas are very small bacteria that are responsible for hundreds of diseases affecting agriculturally important plants around the world. Phytoplasmas are unlike most bacteria, in that they have no cell wall, and they cannot be isolated in laboratory culture. There is need to curb the spread of phytoplasmas and to devise safe measures to control the diseases they cause, but how they cause plant diseases is not understood. In a study of the genome (all of the genes) in a phytoplasma, we have discovered that the genome organization includes a previously unrecognized mosaic of diverse genes that occurs in multiple copies and could account for the rapid evolution of phytoplasmas, as well as the substantial differences among closely related phytoplasmas in the sizes of their genomes. These mosaics, clusters of varied genes, may be related to the ability of phytoplasmas to adapt to their environments and to cause disease. Genes in the clusters provide molecular tools for phytoplasma detection. This work will interest scientists and students studying the evolution of bacteria, plant diseases, and molecular bases of disease mechanisms, as well as to diagnostics companies and centers involved in pathogen detection.
Technical Abstract: Clustering of functionally related genes has long been known in bacterial genomes; this study revealed clustering of diverse, possibly functionally unrelated sequences in the genomes of phytoplasmas -- cell wall-less prokaryotes living as obligate parasites and pathogens of plants and insects. Analysis of the AT-rich genomes of clover phyllody (CPh) and onion yellows (OY-M) phytoplasmas, representing two distinct subgroups of ‘Candidatus Phytoplasma asteris’-related strains, showed that functionally unrelated genes, pseudogenes, mobile genetic elements, intergenic repeat units (IRUs), and phytoplasmal repetitive extragenic palindromes (PREPs) were linked in multiple homologous clusters in both phytoplasma genomes. The tight linkage and putative functions of the sequences suggests that the clusters represent previously unrecognized mosaics assembled through multiple events of horizontal gene transfer, targeted mobile element attack, duplication, rearrangement, and recombination.