Genomic Analysis of Adaptation to an Extreme Terrestrial Environment
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abstract
Organisms have adapted to an astonishing diversity of habitats on our planet. One of the most extreme terrestrial habitats is the result of geological exposures of serpentine rocks, which are the product of chemical and hydrological modification of materials from the Earth''s mantle. Serpentine rocks (and soils derived from these rocks) have extremely limited amounts of a number of essential mineral nutrients, including nitrogen, phosphorous, potassium, and calcium. In addition, they have naturally high levels of toxic ''heavy'' metals such as nickel and chromium. As a result of these multiple chemical challenges, serpentine environments are characterized by poor soil development, low levels of organic matter, and susceptibility to drought. Only a small number of plant, animal and microbial life forms have adapted to the harsh serpentine environment.The Santa Barbara Jewelflower, C. amplexicaulis var. barbarae is a wild plant in the mustard family that is adapted to (and in fact restricted to) serpentine geology. To study the genetic, physiological and molecular mechanisms that underlie adaptation to serpentine habitats, this plant was crossed to its close relative C. amplexicauis var. amplexicaulis, which grows on granite soils and shows 100% mortality on serpentine. Progeny from this cross were used to create an experimental population that showed genetic segregation for several serpentine-tolerance traits, including growth on low calcium, low nitrogen, and low phosphorous, as well as high nickel concentrations. These genetic resources will be used along with next-generation sequencing of all expressed genes (transcriptomics) and whole-genome resequencing to identify the genes and genetic interactions that underlie adaptation to the serpentine environment.The serpentine taxon C. amplexicaulis var. barbarae shows superior growth in low nitrogen and low phosphorous conditions, compared to the non-serpentine C. amplexicaulis var. amplexicaulis. Knowledge of the molecular mechanisms underlying these genetic differences will stimulate new approaches to the development of crops that require smaller applications of nitrogen and phosphorous fertilizers to achieve optimum productivity, and thus help address some of the most pressing agro-environmental issues facing humankind: balancing global food production against pollution by excess application of nitrogen and phosphorous fertilizers (leading to eutrophication, coastal ''dead zones'', coral reef destruction, and other ecological degradation). Further, in laboratory experiments, C. amplexicaulis var. barbarae shows superior tolerance to toxic nickel, and actually hyper-accumulates nickel to extraordinary levels (~1% dry weight). Understanding the genetic mechanisms of heavy metal tolerance and accumulation will provide the foundational science that will foster the development of efficient phytoremediation systems for metal contaminated sites.In collaboration with an educationally innovative high school that encompasses a natural serpentine outcrop with a native population of Caulanthus amplexicaulis var. barbarae, this project will explore a new paradigm for involving students and faculty in authentic collaborative research that is integrated with teaching in mathematics, spatial sciences, earth sciences, and biology.
