Molecular genetic investigation of land plant gravity signaling

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As plants colonized land some 400 million years ago, they evolved the ability to orient the growth of their roots and shoots using the Earth’s gravity vector as a guide. The underlying gravity sensing and response system is not well understood, even though modification of it through selective breeding has importantly shaped today’s crop plants and trees, and future gains in productivity are expected to attend modifications that result in steeper roots better able to reach water sources, and shoots with angles that intercept light better when plants are crowded in high-density production scenarios. This project aims to identify the proteins, which are encoded by genes, that make up the gravity sensing mechanism in the Arabidopsis thaliana plant, which is a model for plants in general. The project builds off of research indicating that a small number of LAZY genes, found only in land plants, encode key components of the gravity signaling system that orients roots and shoots. The project will use experimental methods from the fields of genetics and biochemistry to find genes and their proteins that function with LAZY proteins to create a pathway within cells that translates the gravity vector into a physiological change that steers growth. A clearer view of this pathway’s structure and function will show how plants solved a challenge to living on land, and it will generate opportunities to improve crop plant architecture. Outreach activities will introduce young members of the public to plant responses to gravity.The experimental plan consists of three sections. The first is based on mutations that suppress the severely agravitropic growth of a lazy quadruple mutant. One of the suppressor of lazy quadruple (slq) mutants has been identified, one more is being genetically mapped. SLQ1 negatively regulates LAZY function. SLQ1 expression pattern, subcellular localization, and mechanism of action will be studied, Other SLQs will be similarly studied after they are identified. Another section is based on a functionally-relevant interaction between LAZY1 and a protein called BRXL4 discovered in a yeast two-hybrid (Y2H) screen. The Y2H method will be used to find additional interactors. A proteomic screen will independently identify LAZY1 interactors. Separate approaches used throughout the project are designed to increase the probability of obtaining convergent results. For example, genes identified in a screen for slq mutations may encode proteins that interact physically with LAZY1. The genetic, cellular, and biochemical results will be combined to create a gravity signaling framework. A third section will test mechanistic elements of the framework. The project is expected to establish an unprecedented level of molecular detail about how plants use the gravity vector to guide growth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.