The Role of Chloroplast Gene Expression in Plant Growth and Development

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Chloroplasts play a central role in plant metabolism and in supporting the growth and differentiation of plant cells. Although most chloroplast proteins are encoded in the nucleus, produced in the cytosol, and imported into the chloroplast, few are encoded by the chloroplast genome. Typically, interfering with chloroplast gene function causes defects in photosynthesis, but in some species the effects of such disruptions are more severe and result in early lethality. For example, disrupting chloroplast translation in Arabidopsis often causes embryo lethality, but in other species results in seedlings that are albino, but viable. Recent work suggests that a single chloroplast gene (accD), encoding one subunit of a heteromeric acetyl-CoA carboxylase required for fatty acid biosynthesis, may be responsible for the strikingly different consequences - lethality vs. viable albino - of blocking chloroplast translation in different plant species. This project will evaluate this model, explore its implications for plant biology, and provide valuable insights into basic cellular and metabolic processes that underlie plant development. Several different strategies will be pursued: (1) Determine whether embryo lethality in Arabidopsis mutants defective in chloroplast translation can be rescued by a nuclear transgene encoding a chloroplast-localized version of the normally cytosolic, homomeric carboxylase; (2) Compare the consequences of disrupting chloroplast translation in different accessions of Arabidopsis; and (3) Evaluate plant lineages where accD has been lost from the chloroplast genome. This work will help to illustrate how disrupting genes encoding the same metabolic function in different plant species can have divergent developmental impacts. Results will be published in scientific journals and biological materials distributed to Arabidopsis stock centers. A summer lab course based on this research will be developed to incorporate principles of plant genetics, biochemistry, and evolution, offering biology majors an alternative way to meet lab requirements by focusing on enhanced research, analytical, and writing skills.