Letters to Nature

Nature 430, 205-208 (8 July 2004) | doi:10.1038/nature02703; Received 5 April 2004; Accepted 21 May 2004

Evolutionary change from induced to constitutive expression of an indirect plant resistance

Martin Heil1, Sabine Greiner1,2, Harald Meimberg3, Ralf Krüger1, Jean-Louis Noyer4, Günther Heubl3, K. Eduard Linsenmair2 & Wilhelm Boland1

  1. Department of Bioorganic Chemistry, Max-Planck-Institute for Chemical Ecology, Hans-Knöll-Stras zlige 8, Beutenberg Campus, D-07745 Jena, Germany
  2. Lehrstuhl Zoologie III, Biozentrum, Am Hubland, D-94074 Würzburg, Germany
  3. Department of Biology I, Section: Biodiversity Research, Systematic Botany, LMU Munich, Menzinger Stras zlige 67, D-80638 München, Germany
  4. CIRAD, UMR 1096/PIA, TA 40/03, Avenue Agropolis, F-34398 Montpellier Cedex 5, France

Correspondence to: Martin Heil1 Email: Heil_Martin@web.de
The trnK intron and the trnL–trnF region sequences are published in GenBank under accession numbers AY574092–AY574105 (trnK intron) and AY574106–AY574114 (trnL–trnF region).

Induced plant resistance traits are expressed in response to attack and occur throughout the plant kingdom1, 2. Despite their general occurrence, the evolution of such resistances has rarely been investigated3. Here we report that extrafloral nectar, a usually inducible trait, is constitutively secreted by Central American Acacia species that are obligately inhabited by ants. Extrafloral nectar is secreted as an indirect resistance4, attracting ants that defend plants against herbivores5. Leaf damage induces extrafloral nectar secretion in several plant species6, 7, 8; among these are various Acacia species and other Fabaceae investigated here. In contrast, Acacia species obligately inhabited by symbiotic ants9 nourish these ants by secreting extrafloral nectar constitutively at high rates that are not affected by leaf damage. The phylogeny of the genus Acacia and closely related genera indicate that the inducibility of extrafloral nectar is the plesiomorphic or 'original' state, whereas the constitutive extrafloral nectar flow is derived within Acacia. A constitutive resistance trait has evolved from an inducible one, obviously in response to particular functional demands.

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