Comparative Analysis of C3 and C4 Leaf Development in Rice, Sorghum and Maize

Yale University, New Haven CT

Investigators

Abstract

PI: Timothy Nelson, Yale University Co-PIs: Thomas Brutnell, Boyce Thompson Institute; Klaas van Wijk, Cornell University; Robert Turgeon, Cornell University; Qi Sun, Cornell University; Peng Liu, Iowa State University C4-type plants such as maize, sorghum and several promising biofuel feedstocks possess a set of complex traits that greatly enhance their efficiency of carbon-fixation, water and nitrogen use, and performance in high temperatures and light intensities, in comparison to C3-type plants such as rice and many temperate grasses. The key C4 traits are (1) specialization and cooperation of two leaf photosynthetic cell types (mesophyll and bundle sheath) for carbon fixation and photosynthesis, (2) enhanced movement of metabolites between cooperating cells, and (3) very high density of leaf venation. These C4 traits appear to be regulatory enhancements of features already present in less-efficient C3 plants, but regulated in different patterns. Although C4 plants have evolved at least 50 times independently in various taxonomic groups, the molecular basis of key C4 traits is insufficiently understood to permit their introduction into important C3 plants to enhance their performance as agricultural or biofuel feedstocks. This project will compare the leaves of rice (a C3 grass), maize (a moderate C4 grass) and sorghum (an extreme C4 grass). The abundance and spectrum of gene transcripts, proteins and metabolites will be compared along a developmental gradient from immature tissues at leaf base to mature tissues at the leaf tip. To align the gradients of the three species, markers for developmental time points in gene expression, protein accumulation, sink-source transition and cell wall specialization will be employed. Mesophyll and bundle sheath cells will be obtained from each leaf stage by laser microdissection, and their whole genome RNA transcripts, proteomes (including modifications), and selected metabolites (related to photosynthesis) will be profiled and compared. Two hypotheses will be tested by the comparative analysis of the corresponding C3 and C4 plant datasets: (1) To produce C4 traits, plants use networks of genes, proteins, and metabolites that are already present in C3 plants, and (2) C4 features are plastic and expressed in a degree that depends on environment and developmental stage. This analysis should identify the regulatory points that are potential targets for the production of C4 traits in C3 species. Established and successful summer internship programs (http://bti.cornell.edu/pgrp/, http://www.yale.edu/stars/) will be used to involve undergraduates from under-represented groups in this research. PI/Co-PIs will also participate in curriculum development workshops for high school teachers. Teachers from New York and Connecticut will participate in a one-week program of lectures and discussions to introduce them to plant genomics tools and technologies. These teachers will work with plant science faculty on the Cornell campus to develop genomics-based modules for the classroom. Targeting high school teachers, rather than the students themselves, will greatly extend the reach of this program and will fulfill a primary mission of the NSF: to communicate the significance of the outcomes of plant genome research to society. The project outcomes will be available through a project-specific public website (C3-C4DB, http://c3c4.tc.cornell.edu), and curated into the Gramene public database (http://www.gramene.org). Data will also be deposited at NCBI http://www.ncbi.nlm.nih.gov/ and EBI http://www.ebi.ac.uk/. Teaching modules developed at Cornell will be available through http://bti.cornell.edu/pgrp/pgrp.php?id=601.