Characterization of a wheat cDNA encoding mitochondrial ribosomal protein L11: qualitative and quantitative tissue-specific differences in its expression.

We have cloned a cDNA for a ribosomal protein of wheat that is similar to the bacterial ribosomal protein L11 (RPL11). To determine the subcellular localization of the gene product, we fused the whole cDNA sequence to the coding sequence for Green Fluorescent Protein, and expressed the fusion product transiently in epidermal cells of pea hypocotyls or dayflower leaves. Localized fluorescence was detectable in mitochondria, indicating that this nuclear cDNA encodes a mitochondrial ribosomal protein L11 (MRPL11). In lower protists, mitochondrial RPL11 is encoded by the mitochondrial genome, but higher organisms, including animals, fungi and plants, do not have genes for RPL11 in their mitochondrial genomes, suggesting that transfer of the genetic information for RPL11 from the mitochondrial genome to the nucleus was a very early event in evolution. Transcripts of this wheat gene (TaMRPL11) for mitochondrial RPL11 were found in all tissues examined, although qualitative and quantitative differences in expression were noted. The transcript sizes were different in different plant tissues: 1.0 kb in flowers and roots, and 1.5 kb in shoots. Cold stress transiently increased the steady-state level of TaMRPL11 mRNA in shoots, but the transcription of TaMRPL11 was completely inhibited by cold treatment for longer periods. However, the transcript level in flowers decreased gradually on exposure to low temperature. On the other hand, the accumulation of TaMRPL11 transcripts in roots was not affected by low temperature. These results suggest that the expression of MRPL11 in wheat is regulated precisely, in a tissue-specific manner.

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