Intellectual Merit: Photosynthesis, which harvests solar energy and assimilates atmospheric carbon dioxide (CO2), represents the "engine" of life. Constraints on photosynthesis and plant growth can occur in most land plants where access to CO2 becomes limiting under environmental stress (drought, high temperature, saline soils). Some plants evolved a metabolic pump (called C4) which actively accumulates CO2, conferring an advantage, especially under extreme environments. Prior to the 2001 discovery of species which perform C4 in individual photosynthetic cells, the paradigm for C4 plants was a requirement for cooperative function of two cell types. In contrast, the single-cell C4 species, which have a unique form of carbon acquisition, contain photosynthetic cells with two types of chloroplasts in separate compartments, one supporting the capture of atmospheric CO2, the other functioning in its assimilation into organic matter. Problems to be investigated in this project are identification and characterization of genes and proteins required for the development and function of single-cell C4 photosynthesis. This involves identification of differences in protein composition of the two types of chloroplasts, the nuclear-encoded photosynthetic genes responsible for their synthesis, and the genetic control of chloroplast differentiation. The approach will include use of molecular and microscopic techniques to analyze and identify the products of gene expression leading to development of this form of C4. This project is expected to gain insights into an exceptional mechanism of photosynthesis, and into regulation of biochemical differentiation in cell biology. The research project will also involve an international collaboration with Dr. S. Offermann of Hannover University in Germany, which is sponsored by the International Office of Science and Engineering. This collaboration will provide an international learning experience for the graduate students and will extend the expertise of the US lab. Broader Impacts: The research is expected to contribute new insights that will impact education, future research on photosynthesis, and mechanisms of adaptations in plants. There are potential applications for solving growing global limitations on bio-resources. The single-cell mechanism is an attractive model for developing crops, e.g. rice, with improved productivity, especially under environmental stress.
