Functional and adaptive significance of natural variation in relatives of Arabidopsis

Prof. Tom Mitchell-Olds

Department of Genetics & Evolution, Max Planck Institute of Chemical Ecology, Hans-Knoell-Strasse 8, D-07745 Jena, Germany

Email: tmo@ice.mpg.de

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What evolutionary factors influence insect resistance in natural plant populations? We identified the MAM2 gene, an enzyme-encoding locus responsible for biosynthesis of glucosinolates, biologically active secondary compounds which provide defense against generalist insect herbivores. Fine mapping reveals that MAM2 constitutes an insect resistance QTL, caused by variation in glucosinolate profiles conferred by allelic polymorphism at this locus. A sequence survey of randomly chosen accessions indicates that the MAM2 locus is highly variable among A. thaliana ecotypes. Furthermore, statistical methods of molecular population genetics suggest that MAM2 is subject to balancing selection. This may be caused by ecological trade-offs, i.e., by contrasting physiological effects of glucosinolates on generalist vs. specialist insects.

We then examined a large, undisturbed population of perennial Arabidopsis lyrata. Data from microsatellites and nuclear loci show high levels of molecular variation compatible with equilibrium neutral models. Quantitative genetic variation for morphological and phenological traits also shows very high levels of genetic variance. Little heritable variation for resistance to mustard specialists was found, whereas plant resistance to a generalist herbivore showed highly significant genetic variation. This result corresponds with patterns of insect herbivory in undisturbed natural populations, where specialist insect herbivores cause greater damage than generalists.