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GENETICS, GENOMICS, AND MOLECULAR EVOLUTION

Genotype, Age, Tissue, and Environment Regulate the Structural Outcome of Glucosinolate Activation^1,[W],[OA]

Genetics Graduate Group and Department of Plant Sciences, University of California, Davis, Davis, California 95616

Glucosinolates are the inert storage form of a two-part phytochemical defense system in which the enzyme myrosinase generates an unstable intermediate that rapidly rearranges into the biologically active product. This rearrangement step generates simple nitriles, epithionitriles, or isothiocyanates, depending on the structure of the parent glucosinolate and the presence of proteins that promote specific structural outcomes. Glucosinolate accumulation and myrosinase activity differ by plant age and tissue type and respond to environmental stimuli such as planting density and herbivory; however, the influence of these factors on the structural outcome of the rearrangement step remains unknown. We show that the structural outcome of glucosinolate activation is controlled by interactions among plant age, planting density, and natural genetic variation in Arabidopsis (Arabidopsis thaliana) rosette leaves using six well-studied accessions. We identified a similarly complex interaction between tissue type and the natural genetic variation present within these accessions. This raises questions about the relative importance of these novel levels of regulation in the evolution of plant defense. Using mutants in the structural specifier and glucosinolate activation genes identified previously in Arabidopsis rosette leaves, we demonstrate the requirement for additional myrosinases and structural specifiers controlling these processes in the roots and seedlings. Finally, we present evidence for a novel EPITHIOSPECIFIER PROTEIN-independent, simple nitrile-specifying activity that promotes the formation of simple nitriles but not epithionitriles from all glucosinolates tested.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Daniel J. Kliebenstein (kliebenstein{at}ucdavis.edu).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.115279

^* Corresponding author; e-mail kliebenstein{at}ucdavis.edu.

Received December 20, 2007; accepted March 16, 2008; published March 21, 2008.