mTERF10 and mTERF11, but Not mTERF12, Are Involved in the Response to Salt Stress.

Plastid gene expression (PGE) is crucial for plant development and acclimation to various environmental stress conditions. Members of the "mitochondrial transcription termination factor" (mTERF) family, which are present in both metazoans and plants, are involved in organellar gene expression. contains 35 mTERF proteins, of which mTERF10, mTERF11, and mTERF12 were previously assigned to the "chloroplast-associated" group. Here, we show that all three are localized to chloroplast nucleoids, which are associated with PGE. Knock-down of , or has no overt phenotypic effect under normal growth conditions. However, analysis of , -, and - expression levels points to a possible involvement of mTERF10 and mTERF11 in responses to abiotic stress. Exposing mutant lines for 7 days to moderate heat (30°C) or light stress (400 μmol photons m s) fails to induce a phenotype in mutant lines. However, growth on MS medium supplemented with NaCl reveals that overexpression of results in higher salt tolerance. Conversely, mutants are hypersensitive to salt stress, while plants that modestly overexpress are markedly less susceptible. Furthermore, overexpression leads to enhanced germination and growth on MS medium supplemented with ABA. These findings point to an involvement of mTERF10 in salt tolerance, possibly through an ABA-mediated mechanism. Thus, characterization of an increasing number of plant mTERF proteins reveals their roles in the response, tolerance and acclimation to different abiotic stresses.