Cis-regulatory evolution of Chalcone-synthase expression in the genus Arabidopsis

¹ Max Planck Institute for Plant Breeding Research
² Max Planck Institute for Chemical Ecology
³ Duke University

^* To whom correspondence should be addressed. E-mail: demeaux{at}mpiz-koeln.mpg.de.

Submitted on August 10, 2006
Revised on September 6, 2006
Accepted on 26 September 2006

	Abstract

The contribution of cis-regulation to adaptive evolutionary change is believed to be essential, yet little is known about the evolutionary rules that govern regulatory sequences. Here, we characterize the short term evolutionary dynamics of a cis-regulatory region within and among two closely related species, A. lyrata and A. halleri, and compare our findings to A. thaliana. We focused on the cis-regulatory region of chalcone synthase (CHS), a key enzyme involved in the synthesis of plant secondary metabolites. We observe patterns of nucleotide diversity that differ among species but do not depart from neutral expectations. Using intra- and inter-specific F1 progeny, we have evaluated functional cis-regulatory variation in response to light and herbivory, environmental cues which are known to induce CHS expression. We find that substantial cis-regulatory variation segregates within and among populations as well as between species, some of which resulting from interspecific genetic introgression. We further demonstrate that in A. thaliana, CHS cis-regulation in response to herbivory is greater than in A. lyrata or A. halleri. Our work indicates that the evolutionary dynamics of a cis-regulatory region is characterized by pervasive functional variation, achieved mostly by modification of response modules to one but not all environmental cues. Our study did not detect the footprint of selection on this variation.

Key Words: cis-regulation, herbivory, light response, promoter evolution, pyrosequencing

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