Bacteria Genomes - ONION YELLOWS PHYTOPLASMA

Phytoplasmas associated with yellows diseases were firstly described in 1926 by Kunkle in American aster plants showing virescence and flower malformations. Since then the etiological agent of this and of similar diseases was believed to be a virus;until in 1967 Doi et al. detected under electron microscope phytoplasmas in aster and other plants with "yellows" symptoms opening phytoplasmology history.

Like other mollicutes, phytoplasmas lack cell walls, are pleomorphic and reside endocellularly in insects and plant phloem. Onion yellows phytoplasma is a parasite that lives inside leafhopper insects and spreads to plants through the saliva of feeding insects.

The metabolic pathways and host interactions of Onion yellows phytoplasma is of interest in agricultural and basic sciences. The inability to culture phytoplasmas in vitro has hindered their characterization at the molecular level, the determination of factors involved in their pathogenicity and the discovery of effective ways to control or cure phytoplasma diseases.

Analysis of the phytoplasma genome suggests reductive evolution as a consequence of its life as an intracellular parasite in a nutrient-rich environment and shows that phytoplasma lacks several genes previously considered to be essential for autonomously replicating cells. Instead, it possesses transporter genes involved in the uptake of substances from the cytoplasm of surrounding host cells. Although it is difficult to define the minimal genome concept for pathogens and symbionts that rely on their hosts, phytoplasmas are unique bacteria that contain a new minimal gene set.

References:

Nat. Genet. 36(1):27-29(2004)
http://www.genomenewsnetwork.org/sequenced_genomes/genome_guide_p3.shtml
http://www.uniud.it/phytoplasma/pap/bert8310.Html