Translational Dynamics of Leaf and Chloroplast Development in Maize

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

PI: Alice Barkan (University of Oregon) CoPI: Thomas P. Brutnell (Donald Danforth Plant Science Center) This project will use genetic and genomic approaches to develop "a genome to systems-level understanding of plant-environmental interactions" by exploring how regulated translation contributes to the differentiation of the dimorphic chloroplasts in C4 plants and to maintaining photosynthetic homeostasis under shifting light conditions that compromise photosynthetic efficiency. The focus on maize, a C4 crop plant, is especially pertinent, as C4 photosynthesis likely evolved to reduce photorespiration, resulting in plants that use nitrogen and water more efficiently. Thus a deeper understanding of the regulatory networks driving C4 differentiation will aid in the enhancement of native C4 plants and in engineering C4 traits into C3 crops. With regard to outreach and training, the project will offer educational opportunities for high school, undergraduate and postgraduate students. A laboratory course for University of Oregon undergraduates will be integrated with the large-scale identification of mutations underlying defects in chloroplast biogenesis. A program in St. Louis will engage secondary school students in hands-on analysis of photosynthetic mutants in foxtail millet. Undergraduate, graduate, and postdoctoral students will gain mentored research experience involving cutting-edge genetic, genomic, and molecular approaches. Finally, the project will develop tools and resources for the broader plant genomics research community that include (1) ~6000 new sequence-indexed Mu insertions which can be accessed via MaizeGDB and an in-house search interface (http://teosinte.uoregon.edu/mu-illumina/); (2) a gene identification service for putative Mu-tagged alleles; (3) functional annotations and associated mutant stocks for ~100 maize genes that are essential for photosynthesis; (4) improved genome annotations to be made available through community browsers; and (5) large-scale translatome and transcriptome datasets for the elucidation of coexpression modules and associated functional inferences. Chloroplasts are subcellular organelles in plants that house the machinery for photosynthesis and numerous other essential metabolic processes. Chloroplasts acquire different forms and functions in different cell types, as exemplified by the dimorphic chloroplasts in the bundle sheath and mesophyll cells of C4 plants. They are dynamic organelles that adapt rapidly to changes in the external environment in a manner that optimizes photosynthetic performance while minimizing photo-oxidative damage. This project will elucidate the biogenesis, differentiation, and environmental adaptation of chloroplasts by employing state-of-the-art methods and an extensive collection of non-photosynthetic mutants. Maize is chosen as the experimental organism because it is a C4 plant with dimorphic chloroplasts, it offers a rich collection of chloroplast biogenesis mutants, and the maize leaf blade is an excellent experimental system for describing the developmental progression through which meristematic cells differentiate into photosynthetically-competent leaf cells. The specific objectives of the project are to (1) use a large-scale forward genetic strategy to assign molecular and physiological functions to ~100 genes in maize that are required for photosynthesis; (2) use a state-of-the-art ribosome profiling strategy to define the translatome dynamics underlying the installation of the photosynthetic apparatus and the distinct proteomes in bundle sheath and mesophyll cells; (3) provide a comprehensive description of the progression of mitochondrial and plastid gene expression during the differentiation of photosynthetic leaf tissue; and (4) discover how regulated translation in the cytosol and chloroplast contribute to maintaining photosynthetic homeostasis under shifting light conditions.