The Roles of mTERF Proteins in Chloroplast Gene Expression

The mitochondrial transcription termination factor (mTERF) proteins are tandem degenerate α-helical repeat proteins that are encoded by nuclear genomes of all eukaryotes except fungi. First described in animals in the late 1980s, mTERF proteins are nucleic acid binding proteins that are specifically targeted to mitochondria or chloroplasts where they regulate the expression of organellar genes. While metazoan genomes encode only 3 to 4 mitochondrial-localized mTERF proteins that influence mitochondrial gene transcription or ribosomal assembly and translation, the genomes of higher plants encode more than 30 mTERF proteins that have been associated with various abiotic stress responses. Reverse genetics in Arabidopsis combined with molecular phenotyping and in vitro biochemistry has recently brought considerable clarity into the mechanisms of action of some members of the plant mTERF family in gene expression. In this chapter, we will specifically discuss the results of recent investigations of mTERF functions in plants, focusing on their contribution to chloroplast gene expression.