2007 Annual Report 1a.Objectives (from AD-416) Examine the physiological and genetic impact of manipulating 14-3-3 proteins and sucrose synthase in plants. 1b.Approach (from AD-416) Identify enzyme complexes containing sucrose synthase and examine the impact of molecular genetic manipulation of sucrose synthase on gene expression. Transform Arabidopsis plants with 14-3-3 proteins and examine the impact on plant phenotype in relation to changes in the transcriptome and proteome. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and the University of Illinois. Additional details of research can be found in the report for the parent project 3611-21000-020-00D, Identifying and Manipulating Determinants of Photosynthate Production and Partitioning. Plants are continually producing reactive oxygen species (ROS) that can irreversibly modify cellular components including proteins. Methionine residues in proteins are particularly susceptible to oxidation to methionine sulfoxide (MetSO) converting its side chain from hydrophobic to hydrophilic. Previously, we showed that this could have a significant impact on protein phosphorylation. To further characterize this effect in vivo, we have used transgenic Arabidopsis plants over expressing a repair enzyme that converts MetSO back to methionine. We have now extended this approach to include a knockout of the same gene. Plants having altered expression of PMSRA3 (the repair enzyme) have been tested for ability to respond to various stress conditions. Interestingly, results to date suggest that manipulation of PMSRA3 expression specifically affects plant response to high temperature. Wild type Arabidopsis plants have substantially reduced growth at slightly elevated temperature (28ºC vs 23ºC), whereas over-expressers continued to grow well at the higher temperature. The results suggest that methionine oxidation can be a consequence of stress, such as high temperature, and that specific isoforms of repair enzymes may play unique roles under different conditions. Ultimately, these studies may provide new approaches to increase the stress tolerance of crop plants. Research activities are monitored by the ADODR through weekly meetings with the project participants.