Research Accomplishment Reports 2007

Peptide Deformylase: A Novel Herbicide Target Amenable to Genetically Engineered Tolerance

M. Williams
Department of Horticulture

 

Project Description

Chloroplast-localized peptide deformylase (DEF) has been shown to be an essential co-translational processing enzyme in plants. There are three main experimental objectives in this research project:

1. Produce a detailed biochemical and molecular characterization of chloroplast-localized peptide deformylases.

2. Examine the functional consequences of inhibiting the deformylation of chloroplast proteins to determine how the DEF gene products are essential to plant growth and development.

3. Produce transgenic plants with engineered tolerance to inhibitors of peptide deformylase using conventional over-expression of plant and/or eubacterial peptide deformylase enzymes.

During the last year we have made substantial progress in addressing objectives 1 and 3 (objective 2 was addressed previously).

Objective 3: Tobacco plants have been produced with engineered overexpression of Arabidopsis DEF1 or DEF2. These plants are completely resistant to lethal levels of the known peptide deformylase inhibitor actinonin. These observations provide the first unambiguous evidence that: 1) peptide deformylase activity is essential for plant survival; and 2) that the in vivo molecular target of actinonin is peptide deformylase. With the production of genetically engineered plants overexpressing DEF we now have a system for screening deformylase inhibitors. As a result we have starting screening naturally occurring compounds for deformylase inhibition. Additionally, and perhaps most significantly, we have demonstrated that the combination of plant DEF and DEF inhibitors may represent a native gene selectable marker system for chloroplast and nuclear transformation vectors, and also suggest plant DEF as a potential herbicide target.

Objective 1: We have also successfully obtained the crystal structure of a plant peptide deformylase. This work has provided a detailed structural analysis which has identified a substrate binding cleft that is unique to plant DEF and may have specificity determinants that can be utilized to design inhibitors that are specific to plant deformylases. Results from this work have provided an unequivocal characterization of a plant peptide deformylase and have confirmed that there are differences between plant DEF and other DEFs.

Impact

Our research in peptide deformylase has recently achieved a milestone with the production of transgenic plants with engineered resistance to the herbicidal effects of peptide deformylase inhibitors. The over-expression of peptide deformylase genes has conclusively been demonstrated to confer herbicide tolerance. This is the first confirmation of the use of this technology as a new weed control system. This technology, which is analogous to the widely-used herbicide Roundup (glyphosate) and Roundup-ready crops, could create a new highly efficacious weed control system applicable to many commercially grown agronomic and horticultural crops.

This study also provides evidence that the combination of peptide deformylase and peptide deformylase inhibitors can be successfully used as a selectable marker system which circumvents the necessity for foreign genes or antibiotic resistance. Additionally the detailed analysis of the recently obtained crystal structure of a plant deformylase will provide the necessary information to direct the design of these new herbicidal products. The ultimate realization of these goals will be the production of a weed management system utilizing the expression of endogenous plant genes and plant-specific herbicidal inhibitors.

Publications

Hou, Cai-Xia, Dirk, M. A., Pattanaik, S., Das, N., Maiti, I., Houtz, R. and Williams, M. (2007) Plant Peptide Deformylase: a Novel Selectable Marker and Herbicide Target Based on Essential Cotranslational Chloroplast Protein Processing. Plant Biotech. J. 5: 275-281.

Dirk, M. A., Schmidt, J., Cai, Y., Barnes, J., Hanger, K., Williams, M., Grossman, R., Houtz, R., Rodgers, D. (2007) Crystal Structure of Plant Peptide Deformylase. Accepted for publication in Biochemical J. (in press).