Linking Calcium Sensor Gene Duplication and Functional Divergence to Plant Salt Tolerance

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Soil salinity affects over 6% of the world's land mass, and currently causes the loss of at least three hectares of arable land worldwide each minute. It has been estimated that, in the United States alone, soil salinity reduces irrigated crop yields by 20-30% annually. With few exceptions, crop plants are unable to adapt to the stresses induced by elevated levels of salt in the soil. While genetic variation for plant growth in salinity (salt tolerance) exists, little is known about the genes underlying this variation. Two copies of a calcium sensor gene has been found in the plant species Eutrema salsugineum, while many related species have only one copy. Because Eutrema is able to grow in high salt soils that kill most, if not all crop plants, the duplication of this gene provides a unique opportunity to link its function to plant salt tolerance. To do this, the project will uncover how and when the functions of the original and duplicate genes diverged and identify the physiological changes that resulted. In addition, this project will be used to enhance the infrastructure of research, training, and outreach through the continued education and training of students and postdoctoral researchers at the University of Arizona, design of simple research modules for largely minority-serving K-12 classrooms in the Tucson area, and participation in outreach efforts to K-12 students and the community in Southern Arizona.Gene duplication is a major source of genetic diversity and, consequently, adaptive evolution. Because most duplicated genes are lost via pseudogenization, the maintenance of duplicated gene pairs in a genome can be indicative of an adaptive benefit conferred by the paralogous genes. The CBL10 calcium sensor is present as a single gene in the salt-sensitive model plant Arabidopsis thaliana (Arabidopsis), but as two genes in its salt-tolerant relative, Eutrema (both members of the Brassicaceae). This project will use the genetic and genomic resources developed for Arabidopsis to determine how new traits and phenotypes emerge from a gene duplication event and contribute to plant adaptation. Specifically, characterization of Eutrema with reduced expression of the CBL10 genes will determine their specific functions in salt tolerance (Aim 1). Functional analysis of CBL10 homologs from closely related species within the Brassicaceae will determine when the duplicated Eutrema genes acquired the changes that led to their functional divergence (Aim 2). Analyses of CBL10 protein sequences and biochemical activities will identify domains that underlie the differences in Eutrema CBL10 function and the associated physiological mechanisms (Aim 3).