Identification of a mitochondrial ATP synthase small subunit gene (RMtATP6) expressed in response to salts and osmotic stresses in rice (Oryza sativa L.)

Large areas of northern China have alkaline soil due to the accumulation of sodium carbonates (NaHCO3, Na2CO3). To understand better how plants can tolerate alkaline soil, a cDNA library was prepared from rice (Oryza sativa L.) roots grown in the presence of NaHCO3 stress. A cDNA clone isolated from this library was identified by a homology search as a mitochondrial ATP synthase 6 kDa subunit gene (RMtATP6; GenBank accession nos AB055076, BAB21526). In transformed yeast and tobacco protoplasts, the RMtATP6 protein was localized in mitochondria using the green fluorescent protein (GFP) marker. Analysis of RMtATP6 mRNA levels suggested that the expression of this gene was induced by stress from sodium carbonates and other sodium salts. Transgenic tobacco overexpressing the RMtATP6 gene had greater tolerance to salt stress at the seedling stage than untransformed tobacco. Among the other genes for F1F0-ATPase of rice, some were found to be up-regulated by some environmental stresses and some were not. These data suggest that the RMtATP6 protein acts as a subunit of ATP synthase, and is expressed in response to stress from several salts, with the other genes coding for the subunits of the same ATP-synthase.