Ecological genomics of adaptive responses of sunflower to the environment

Soil fertility is an important factor driving plant ecological performance and evolutionary change in natural and managed ecosystems. We are studying the evolutionary ecophysiology of plant nutrient relation traits in infertile habitats, using a desert sunflower species. Helianthus anomalus is a homoploid hybrid from ancestral parents H. annuus and H. peiolaris. Compared to its ancestral parent species, H. anomalus is endemic to a low nutrient habitat, does better in that habitat than its ancestral parents, and has some traits consistent with low nutrient adaptation. Additionally, we have found genetic variation (quantitative trait loci, QTL) for some of the traits under high resource conditions and demonstrated that some of the traits are under phenotypic selection in the H. anomalus habitat. We are currently investigating the outcome of selection on traits putatively adaptive in a low nutrient environment, by comparing H. anomalus to its ancestral parents under low and high nutrient conditions. Traits include leaf ecophysiological traits, allocation, and RGR carbon and nitrogen economy components. Candidate genes underlying these traits are being targeted with gene expression analysis using microarrays. Of greatest interest are those genes that respond differently to nutrient stress in the hybrid as compared to the response of ancestral parents. We also plan to identify QTL for nutrient relation traits under low and high nutrient conditions, using a diverse synthetic hybrid population (F2, H. annuus x H. petiolaris). We will further investigate selection on nutrient relation traits using artificial selection and phenotypic selection analysis. The integration of ecophysiological, quantitative genetic, and genomic perspectives is providing insights into the evolutionary forces that have shaped H. anomalus, and more generally to the process of selection that leads to adaptation to low nutrient habitats.