The eroded genome of a Psychotria leaf symbiont: hypotheses about lifestyle and interactions with its plant host
Article first published online: 2 MAY 2012
© 2012 Society for Applied Microbiology and Blackwell Publishing Ltd
Thematic issue: Sulfur Metabolism
Volume 14, Issue 10, pages 2757–2769, October 2012
How to Cite
Carlier, A. L. and Eberl, L. (2012), The eroded genome of a Psychotria leaf symbiont: hypotheses about lifestyle and interactions with its plant host. Environmental Microbiology, 14: 2757–2769. doi: 10.1111/j.1462-2920.2012.02763.x
- Issue published online: 3 OCT 2012
- Article first published online: 2 MAY 2012
- Received 5 October, 2011; revised 3 March, 2012; accepted 1 April, 2012.
Several plant species of the genus Psychotria (Rubiaceae) harbour Burkholderia sp. bacteria within specialized leaf nodules. The bacteria are transmitted vertically between plant generations and have not yet been cultured outside of their host. This symbiosis is also generally described as obligatory because plants devoid of symbionts fail to develop into mature individuals. We sequenced for the first time the genome of the symbiont of Psychotria kirkii in order to shed some light on the nature of their symbiotic relationship. We found that the 4 Mb genome of Candidatus Burkholderia kirkii (B. kirkii) is small for a Burkholderia species and displays features consistent with ongoing genome erosion such as large proportions of pseudogenes and transposable elements. Reductive genome evolution affected a wide array of functional categories that may hinder the ability of the symbiont to be free-living. The genome does not encode functions commonly found in plant symbionts such as nitrogen fixation or plant hormone metabolism. Instead, a collection of genes for secondary metabolites' synthesis is located on the 140 kb plasmid of B. kirkii and suggests that leaf nodule symbiosis benefits the host by providing protection against herbivores or pathogens.