Biomedical subjects
Publications and source records attributed to G Takeba.
CRR12 was identified as a cytokinin-repressed gene encoding a cucumber homologue for a basic region/helix-loop-helix protein. The level of CRR12 mRNA decreased in response to either cytokinins or light in etiolated cotyledons. The level was low in cotyledons and leaves of light-grown plants, but it increased during dark incubation.
The gene encoding nitrate reductase was cloned from the DNA isolated from cultured spinach (Spinacia oleracea cv. Hoyo) cells and sequenced. The clone contains 7612 nucleotides of the gene which consists of four exons interrupted by three introns. The transcription start site was determined by primer extension analysis and located 193 bp upstream of the ATG translation initiation codon. The 5'-flanking region contains a TATA box and CAAT box.
The CR20 gene was identified as a cytokinin-repressed gene in excised cotyledons of cucumber. We determined the sequences of some CR20 cDNAs with different structures and sequenced genomic clones for CR20. This gene consisted of three exons, and there were at least three types of transcript, which seemed to be generated by alternative splicing of the second intron. None of the CR20 transcripts included a long open reading frame (ORF). We isolated a cDNA of Arabidopsis thaliana with cucumber CR20 cDNA as a probe. This cDNA for a gene designated AtCR20-1 also lacked a long ORF. A region of 180 nucleotides was conserved in the CR20 RNA of cucumber and the AtCR20-1 RNA of Arabidopsis, although the homology was relatively low when the entire sequences were compared. Each conserved region consisted of seven elements, and seems to form stable secondary structure. These suggest that CR20 RNA may function as an RNA that is not translated into a protein.
A cDNA clone for an mRNA whose level increased within 2 h of the start of treatment with N6-benzyladenine in etiolated cotyledons of cucumber was isolated by differential hybridization. The cDNA was homologous to psaL, which encodes subunit XI (PSI-L) of photosystem I. The accumulation of psaL mRNA was specifically induced by cytokinins or light.
Large-scale differential hybridization was performed to examine rapid changes in gene expression caused by a phytohormone, cytokinin, in etiolated cotyledons of cucumber (Cucumis sativus L.). We isolated 86 cDNA clones for mRNAs whose levels decreased within 2 h of the start of treatment with N6-benzyladenine (BA). Partial nucleotide sequences showed that some of the cDNAs were homologous to those for catalase, 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and a lectin. This is the first report that the levels of the mRNAs for those proteins are regulated by a cytokinin in darkness. Together with previous results [Teramoto et al. (1993) Physiol. Plant. 87: 584, (1994) Planta 193: 573, (1995) Planta 196: 387], the present study suggests that the cytokinin act to lower the levels of mRNAs transcribed from various genes in etiolated cotyledons.
Rapid changes in gene expression were studied during incubation of cucumber (Cucumis sativus L.) cotyledons with cytokinins in darkness. Complementary-DNA clones for mRNAs whose levels decreased within 4 h of treatment with N6-benzyladenine (BA) were isolated by differential hybridization. One of them (CR9) was sequenced. It is 588 bp long, and would encode a protein consisting of 137 amino-acid residues and having a molecular mass of 15 kDa. The sequence shows a high homology with a light-induced gene from rice. Northern blot analysis of the CR9 transcript showed the level of the mRNA (0.7 kb) to decrease tenfold within 4 h of BA treatment, i.e. well before BA-induced cotyledon expansion was observed. The repression became greater with increasing concentration of BA (10(-8)-10(-5) M). The expression of the CR9 gene was repressed specifically by cytokinins (BA, isopentenyladenine and t-zeatin), but not by adenine or 2,4-dichlorophenoxyacetic acid (auxin). The results are discussed in relation to the primary action of cytokinin.
A full-length cDNA encoding glutamine synthetase was isolated from a lambda gt11 library constructed from the poly(A)+ RNA isolated from lettuce seeds incubated under red light. The nucleotide sequence of the cDNA and the deduced sequence of amino acids showed a high degree of homology to those of the cytosol-type glutamine synthetase from other plants. Northern and dot-blot analyses of poly(A)+ RNA extracted from the seeds incubated under various light conditions showed that the activation of the gene for cytosolic glutamine-synthetase during imbibition of lettuce seeds is directly or indirectly regulated by phytochrome.
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