CAREER: Defining Critical Transport Mechanisms for Chloroplast Osmoregulation and Salt Stress Response

Washington State University, Pullman WA

Investigators

Abstract

Plants are a prerequisite for life on earth. By performing photosynthesis in the chloroplast, a specialized cell compartment, plants transform light into chemical energy and fix CO2 from the atmosphere. Furthermore, they provide the air we breathe by releasing oxygen, and they represent the main part of our diet. As sessile life forms, plants have to cope with constantly changing, often times harsh, environments. As average temperatures rise, drought and interrelated soil salinity become increasingly problematic for plant performance and agricultural production in the US and globally. Salt stress affects photosynthesis by destroying the fine-tuned ion balance in the chloroplast. This process involves transporter proteins but most genes encoding chloroplast ion transporters are unknown. Dr. Kunz and his group investigate a new set of plant genes and mutants to determine their role in chloroplast ion transport. Moreover, his group is building a genetic tool that allows for testing the relevance of all chloroplast proteins and entire protein families in plant function and photosynthesis. The tool will be applied to precisely determine the genes crucial for plant performance under salt stress. This research will provide critical knowledge and new strategies to increase crop yields even under adverse climatic conditions. Dr. Kunz engages high school students in his research to raise awareness for plant research and its significance for a sustainable future and to excite the future generation of scientist for the world's most fundamental biochemical process, photosynthesis. Plant photosynthesis is affected by soil salinity but little is known about the genes involved and their potential to improve plant resistance. Salt stress triggers changes in transcription of nuclear encoded chloroplast genes and the chloroplast proteome. Physiologically, salt stress leads to toxic Na+ accumulation in plastids and outcompeting of K+ which disturbs chloroplast ion homeostasis, osmoregulation, and eventually diminishes photosynthetic efficiency. Recently, the first plastid K+ efflux carriers were discovered. Corresponding loss-of-function mutant plants reveal poor photosynthesis under control conditions but, surprisingly, photosynthesis is rescued by salt stress. This emphasizes the potential of manipulating plastid ion flux to increase photosynthetic efficiency during salt stress. However, this approach is hindered by the limited number of characterized plastid ion transporters, most strikingly a chloroplast K+ importer. One hurdle is the high number of gene family members in chloroplasts which often results in functional redundancy and a lack of phenotypes. This project will: 1. Determine the role of plastid K+ channel homologs for K+ import, 2. Define the genes responsible for the unexpected salt stress rescue of plastid K+ efflux carrier mutants. 3. Build and apply a full-coverage artificial library tool to downregulate all nuclear encoded chloroplast genes and gene family transcripts in Arabidopsis thaliana and determine the genes responsible for plastid Na+ influx and low photosynthesis during salt stress. 4. Engage and excite high school students in plant science and photosynthesis by providing hands-on molecular biology training in the classroom and the laboratory.