Genetic Analysis of Natural Variation in the Control of Water Use Efficiency and Response to Drought Stress in Brassica rapa

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PI: C. Robertson McClung (Dartmouth College)CoPIs: Cynthia Weinig and Brent E. Ewers (University of Wyoming), Richard M. Amasino (University of Wisconsin - Madison), and Todd C. Mockler (Oregon State University)This project investigates the genetic underpinnings of plant water use in the crop species Brassica rapa. Water-use efficiency is a critical determinant of yield in crops and fitness in wild species. The match between a plant's endogenous circadian rhythm and external abiotic conditions, including water stress, can dramatically affect physiological functions such as chlorophyll production, carbon fixation, and water loss through transpiration. Brassica rapa exhibits a strong association between circadian rhythms and both transpiration and water-use efficiency. Preliminary studies exploiting the genetic diversity present in two parental genotypes have identified at least ten genetically defined regions that affect water-use efficiency. Of these, six co-localize with genes affecting circadian clock function. This project will clone and characterize the gene or genes of one region, on Chromosome A7, that explains more than one-quarter of the variation in water-use efficiency. Identifying the underlying locus will be facilitated by experiments where water stress is imposed at the atmospheric and soil levels, and plant measurements quantify the connection between water supply and demand as well as plant carbon fixation and utilization. This project also will characterize the gene expression response to water stress and the influence of time of day on the magnitude of that response. This project will develop genetic resources akin to the maize Nested Association Mapping (NAM) lines that will explore the genetic diversity present in ~20 diverse parents. This should allow the identification of more genetic loci that contribute to water-use efficiency. These in turn will be fine-mapped and cloned, thus enhancing our understanding of the genetic basis of water-use efficiency in crop species. Enhanced understanding of the architecture of water-use efficiency in this crop species should facilitate efforts to breed for enhanced water-use efficiency in a wide range of crop species.Given the profound implications to society of even small changes in crop water use on global hydrology, a thorough understanding of the genetic controls on and natural variation in plant water use and gas exchange is warranted to feed a rapidly growing global population with increasingly limited fresh water supplies. This project offers innovative educational opportunities at the high school, undergraduate, predoctoral and postdoctoral levels in quantitative molecular and classical genetic analysis and plant physiology. The project will train middle and high school teachers and develop educational modules that permit K-16 students to do hands on studies in classical and molecular genetics using a rapid-cycling strain of B. rapa. Annual summer institutes at University of Wisconsin - Madison will enhance the value of a resource to teach classical, molecular, and biochemical genetics at the K-12 and undergraduate levels that has already gained widespread acceptance in the classroom. Thus, the outreach aspects of this project should be manifest on a national level. All data, biological materials, and teaching materials will be freely available through the DIURNAL website (http://diurnal.cgrb.oregonstate.edu/diurnal_about.html), public databases [NCBI Short Read Archive (SRA) (http://www.ncbi.nlm.nih.gov/Traces/sra/sra.cgi?), Gene Expression Omnibus (GEO) (http://www.ncbi.nlm.nih.gov/geo/), Brassica.info (www.brassica.info)] and/or repositories [Arabidopsis Biological Resource Center (ABRC) (http://abrc.osu.edu/) and the Wisconsin Fast Plants Program (WFPP) (http://www.fastplants.org/)].