Research Summary

Plastid Molecular Genetics

Plastids of higher plants are genetically semi-autonomous: ~120 genes are encoded in the ~ 155-kb plastid genome (ptDNA) while most functions are encoded in ~ 3,000 nuclear genes targeting proteins to plastids. The technology of plastid transformation in higher plants was developed in our laboratory during the early 1990s using tobacco (Nicotiana tabacum) as the model system. Plastid transformation was used to probe plastid gene function. Early research highlights included demonstration of the functioning of two distinct transcription machineries: a multi-subunit, plastid-encoded RNA polymerase (PEP) encoded by the plastid genome and the nuclear-encoded, single-subunit RNA polymerase (NEP). Plastid transformation provided the first experimental tool to study cis sequences and trans factors involved in plastid cytosine-to-uridine editing, a process that post-transcriptionally alters a small number of codons to correct mutations in the plastid DNA and to provide for regulatory functions. In the course of this research we developed new expression tools for industrial-scale production of recombinant proteins in tobacco chloroplasts (see patents below). Our plastid and nuclear (Agrobacterium) transformation vectors have been distributed worldwide. The pPZP family of Agrobacterium binary vectors (Plant Molecular Biology 25: 989, 1994) was listed among the top 30 plant technology studies in 2007 (Plant Biotechnology Journal 5: 221, 2007).
   Currently we evaluate plastid transgene biosafety and explore plastid marker gene excision with phage site-specific recombinases supported by the USDA Biotechnology Risk Assessment Research Grant Program. For more information see our 2006-2007 Annual Report and a recent press release. Our long-term interest is the molecular dissection of the processes that control plastid inheritance. This research in wood tobacco (Nicotiana sylvestris) and Arabidopsis thaliana will lead to new molecular-genetic approaches to enhance the stringency of uniparental-maternal inheritance of plastids in crop plants, thereby improving containment of transgenes encoded in the plastid genome. We are also interested in engineering metabolic pathways by exploiting plastid localization of transgenes and the plastid’s unique transcription and translation machinery. We are currently testing if increased levels of free methionine and folate can be obtained by manipulating the tetrahydrofolate-bound one-carbon units in tobacco chloroplasts in collaboration with Dr. Sanja Roje, Washington State University, Pullman, WA.

Dr. Pal Maliga, Professor
Dr. Zora Svab, Research Associate
Dr. Tarinee Tungsuchat, Research Assistant
Csanad Gurdon, Graduate Fellow
Kerry Lutz, Graduate Fellow
Sugey Sinagawa, Graduate Fellow
Gregory Thyssen, Graduate Fellow

Selected scientific publications since 1996
Publications in Medline click here
US Patents since 1995