Genomic analysis of aminotransferases in Arabidopsis thaliana

Aminotransferases are an important and diverse group of proteins. Of the approximately 25,000 predicted proteins in the Arabidopsis proteome, it is estimated that 4,000 are involved in cellular metabolism. Sequence analyses predict that roughly one percent of the metabolism sequences of Arabidopsis encode aminotransferases. Many plant aminotransferase genes have been identified, and their corresponding gene products have been localized and characterized. These studies have implicated aminotransferase reactions in a diverse variety of pathways in plants, including such primary metabolic pathways as amino acid biosynthesis and catabolism, photorespiration, and vitamin biosynthesis, as well as carbon and nitrogen shuttles, and plant stress responses. Thus, these enzymes may be reasonable targets for metabolic engineering to produce crop varieties with enhanced stress resistance and nutrient content. In addition, several aminotransferases that are absent from animals may be excellent targets for herbicides. The first part of this review focuses on recent progress on the identification and characterization of aminotransferases from Arabidopsis and other plants. There is still much to learn about plant aminotransferases; in Arabidopsis more than 40% of the aminotransferase-like sequences remain uncharacterized. The second part of this review discusses uncharacterized aminotransferase-like sequences in the Arabidopsis genome. Although it is not yet possible to predict the reactions catalyzed by these uncharacterized aminotransferases based on sequence alone, potential functions of these putative aminotransferases are discussed in light of sequence motifs, publicly available transcript expression data, and sequence similarity to characterized homologs from other organisms.