Characterization of a wheat cDNA encoding mitochondrial ribosomal protein L11: qualitative and quantitative tissue-speci
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O R I GI N A L P A P E R
H. Handa á A. Kobayashi-Uehara á S. Murayama
Characterization of a wheat cDNA encoding mitochondrial ribosomal protein L11: qualitative and quantitative tissue-speci®c differences in its expression Received: 6 October 2000 / Accepted: 8 January 2001 / Published online: 14 March 2001 Ó Springer-Verlag 2001
Abstract 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 day¯ower leaves. Localized ¯uorescence 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 dierences in expression were noted. The transcript sizes were dierent in dierent plant tissues: 1.0 kb in ¯owers 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 ¯owers decreased gradually on exposure to low temperature. On the other hand, the accumulation of Communicated by R. Hagemann H. Handa (&) á A. Kobayashi-Uehara á S. Murayama Laboratory of Plant Genecology, Hokkaido National Agricultural Experiment Station, Sapporo 062-8555, Japan E-mail: [email protected]rc.go.jp Tel.: +81-11-8579211 Fax: +81-11±8592178 H. Handa Laboratory of Plant Genecology, Hokkaido National Agricultural Experiment Station, 1, Hitsuji-ga-oka, Toyohira-ku, Sapporo 062-8555, Japan
TaMRPL11 transcripts in roots was not aected by low temperature. These results suggest that the expression of MRPL11 in wheat is regulated precisely, in a tissuespeci®c manner. Keywords Plant mitochondria á Ribosomal protein á Wheat á Tissue-speci®c expression á RPL11
Introduction Biogenesis of plant mitochondrial ribosomes requires protein components encoded by both the nuclear and mitochondrial genomes, so that coordinated regulation is needed for the expression of ribosomal protein genes distributed between the two compartments. For instance, 16 and 7 ribosomal protein genes have been identi®ed in the mitochondrial genomes of Marchantia polymorpha and Arabidopsis thaliana, respectively (Takemura et al. 1992; Unseld et al. 1997). The protozoon Reclinomonas americana possesses 27 ribosomal protein genes in its mitochondrial genome, which is sugge
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