title: The genome sequence of the leaf-cutter ant Atta cephalotes reveals insights into its obligate symbiotic lifestyle.
abstract: Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the formation of their massive colonies. Mature leaf-cutter ant colonies contain millions of workers ranging in size from small garden tenders to large soldiers, resulting in one of the most complex polymorphic caste systems within ants. To begin uncovering the genomic underpinnings of this system, we sequenced the genome of Atta cephalotes using 454 pyrosequencing. One prediction from this ant's lifestyle is that it has undergone genetic modifications that reflect its obligate dependence on the fungus for nutrients. Analysis of this genome sequence is consistent with this hypothesis, as we find evidence for reductions in genes related to nutrient acquisition. These include extensive reductions in serine proteases (which are likely unnecessary because proteolysis is not a primary mechanism used to process nutrients obtained from the fungus), a loss of genes involved in arginine biosynthesis (suggesting that this amino acid is obtained from the fungus), and the absence of a hexamerin (which sequesters amino acids during larval development in other insects). Following recent reports of genome sequences from other insects that engage in symbioses with beneficial microbes, the A. cephalotes genome provides new insights into the symbiotic lifestyle of this ant and advances our understanding of host-microbe symbioses.
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America. gsuen@wisc.edu
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authors.lastname: Suen
authors.forename: Clotilde
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authors.forename: Marie-Julie
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authors.forename: Sarah E
authors.initials: SE
authors.lastname: Marsh
authors.forename: Joseph A
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authors.lastname: Moeller
authors.forename: Mónica C
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authors.lastname: Muñoz-Torres
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authors.forename: Meredith C
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authors.lastname: Naughton
authors.forename: Surabhi
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authors.lastname: Nigam
authors.forename: Rick
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authors.lastname: Overson
authors.forename: Rajendhran
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authors.lastname: Rajakumar
authors.forename: Justin T
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authors.lastname: Reese
authors.forename: Jarrod J
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authors.lastname: Scott
authors.forename: Chris R
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authors.lastname: Smith
authors.forename: Shu
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authors.lastname: Tao
authors.forename: Neil D
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authors.lastname: Tsutsui
authors.forename: Lumi
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authors.lastname: Viljakainen
authors.forename: Lothar
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authors.lastname: Wissler
authors.forename: Mark D
authors.initials: MD
authors.lastname: Yandell
authors.forename: Fabian
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authors.lastname: Zimmer
authors.forename: James
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authors.lastname: Taylor
authors.forename: Steven C
authors.initials: SC
authors.lastname: Slater
authors.forename: Sandra W
authors.initials: SW
authors.lastname: Clifton
authors.forename: Wesley C
authors.initials: WC
authors.lastname: Warren
authors.forename: Christine G
authors.initials: CG
authors.lastname: Elsik
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Smith
authors.forename: George M
authors.initials: GM
authors.lastname: Weinstock
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Gerardo
authors.forename: Cameron R
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authors.lastname: Currie
mesh_terms: D000818:Animals; D001000:Ants / Q000235:genetics / Q000502:physiology*; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D005658:Fungi / Q000235:genetics; D049750:Genome, Insect / Q000235:genetics*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D017422:Sequence Analysis, DNA; D057057:Serine Proteases / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis
chemical_list: D019476:Insect Proteins; C041137:storage proteins, Insecta; D001120:Arginine; D057057:Serine Proteases