Citrus pest's little helper

Nature 499, 257 (18 July 2013)

doi:10.1038/499257c

Published online

17 July 2013

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A notorious agricultural pest harbours a bacterium that produces a toxin which may deter its predators. Orange-grove farmers dread the Asian citrus psyllid (Diaphorina citri), a small insect that carries the bacterial disease huanglongbing, which ruins citrus crops. Atsushi Nakabachi at Toyohashi University of Technology in Japan and his colleagues…

Subject terms:

• Ecology

READ THE FULL ARTICLE Defensive Bacteriome Symbiont with a Drastically Reduced Genome

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Current Biology, 11 July 2013

Copyright © 2013 Elsevier Ltd All rights reserved.

10.1016/j.cub.2013.06.027

Authors

Atsushi Nakabachi ,Reiko Ueoka,Kenshiro Oshima,Roberta Teta,Alfonso Mangoni,Mihaela Gurgui,Neil J. Oldham,Gerhild van Echten-Deckert,Keiko Okamura,Kohei Yamamoto,Hiromitsu Inoue,Moriya Ohkuma,Yuichi Hongoh,Shin-ya Miyagishima,Masahira Hattori,Jörn Piel,Takema FukatsuSee Affiliations

• Highlights

• The Asian citrus psyllid has a dual symbiotic system with Carsonella and Profftella

• Profftella is a defensive symbiont with an extremely reduced 460 kb genome
• As much as 15% of the small Profftella genome is devoted to toxin biosynthetic genes
• Profftella acquired the toxin biosynthetic genes through horizontal gene transfer

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Summary

Diverse insect species harbor symbiotic bacteria, which play important roles such as provisioning nutrients and providing defense against natural enemies [1,2,3,4,5,6]. Whereas nutritional symbioses are often indispensable for both partners, defensive symbioses tend to be of a facultative nature [1,2,3,4,5,6,7,8,9,10,11,12]. The Asian citrus psyllid Diaphorina citri is a notorious agricultural pest that transmitsLiberibacter spp. (Alphaproteobacteria), causing the devastating citrus greening disease or Huanglongbing [13,14]. In a symbiotic organ called the bacteriome, D. citri harbors two distinct intracellular symbionts: a putative nutrition provider, Carsonella_DC (Gammaproteobacteria), and an unnamed betaproteobacterium with unknown function [15], for which we propose the name “Candidatus Profftella armatura.” Here we report that Profftella is a defensive symbiont presumably of an obligate nature with an extremely streamlined genome. The genomes of Profftella and Carsonella_DC were drastically reduced to 464,857 bp and 174,014 bp, respectively, suggesting their ancient and mutually indispensible association with the host. Strikingly, 15% of the small Profftella genome encoded horizontally acquired genes for synthesizing a novel polyketide toxin. The toxin was extracted, pharmacologically and structurally characterized, and designated diaphorin. The presence of Profftella and its diaphorin-biosynthetic genes was perfectly conserved in the world’s D. citri populations.