Regulation of nutrient homeostasis by the CBL-CIPK calcium sensor-kinase network in Arabidopsis

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Plant growth requires a balanced supply of mineral nutrients but today’s soil is often deficient in essential minerals such as nitrogen, phosphorus (P), and potassium (K+). Crop production heavily relies on use of fertilizers but excessive fertilizer use is costly, endangers environmental health, and it is not sustainable because some essential minerals (e.g., potash and phosphorus rock) are limited natural resources. As an alternative strategy, breeding plants with new traits enabling them to grow in nutrient-imbalanced soil, has become a global focus for long-term solution to sustainable agriculture. To achieve this goal, we need to understand the molecular networks that allow plants to respond and adapt to the constantly changing status of mineral nutrients in the soil. In other words, we need to know how plants maintain the homeostasis of mineral nutrients when soil contains too much or too little of specific minerals. This project will address the genetic and molecular mechanisms underlying plant adaptation to soil nutrient availability, thereby establishing the knowledgebase for breeding crops with little need of fertilizers, thus supporting sustainable agriculture. The research will have an additional impact on undergraduate and graduate education through major courses the principal investigator teaches at the University of California, Berkeley and through independent research programs in his laboratory. The NSF project will also enhance the efforts that focus on local high schools to encourage students underrepresented in science to pursue higher education and explore biology research as a career option. A summer workshop for high school students has been ongoing for ten years and will continue under this project. Graduate students-led effort “CAL Students for Minority Success” outreaches mainly Hispanic students in the local high schools on general science education. Summer research training of URM students through Biotech Partners will also continue. This combination of activities will help promote success in education for these students. Plants constantly monitor nutrient status in the soil and maintain nutrient homeostasis by controlling ion transport across the plasma membrane (for uptake) and tonoplast (for storage and remobilization). However, the signaling mechanism linking nutrient status in the soil and membrane transport in plants is largely unknown. The principal investigator’s laboratory discovered the CBL-CIPK calcium signaling network that functions in a number of cellular pathways including nutrient sensing. Their NSF-supported studies connected the CBL-CIPK signaling mechanism to the regulation of transport activities at the plasma membrane and vacuolar membrane (tonoplast), the two most important sites for nutrient homeostasis in plant cells. Experimental evidence also emerged for new signaling crosstalk, at the early stage of nutrient sensing, between the CBL-CIPK modules and other signaling kinases and phosphatases. The proposed research will pursue these exciting new leads with the following specific objectives: 1. To identify the molecular mechanism by which CBL-CIPK regulates the activity of K-transporters in the vacuolar membrane. 2. To identify the transporters targeted by CBL-CIPK signaling modules for vacuolar Mg sequestration. 3. To understand the early events of low-K response that activates CBL-CIPK modules. 4. To examine the functional relationship between the CBL-CIPK modules at the plasma membrane and those at the tonoplast. The research will benefit from the unique expertise of the PI group in the model plant systems that are amenable to patch-clamp and cell biology analysis in combination with genetic and biochemical approaches.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.