Development of structural and biochemical characteristics of C(4) photosynthesis in two types of Kranz anatomy in genus Suaeda (family Chenopodiaceae).
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Organ-specific transcripts of different size and abundance derive from the same pyruvate, orthophosphate dikinase gene in maize.
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Analyses of genomic DNA and clones indicate that the pyruvate, orthophosphate dikinase (PPDK; ATP: pyruvate, orthophosphate phosphotransferase, EC 2.7.9.1) gene family of maize (Zea mays L. subsp. mays, line B73) contains two members. Restriction site and DNA sequence comparisons between PPDK genomic and leaf cDNA clones have revealed which gene encodes the isozyme involved in C4 photosynthesis. The region flanking the 5' end of this gene contains two 30-base-pair (bp) repetitive elements that may be involved in its light-regulated expression. Sequence analysis of genomic and leaf cDNA clones has also shown that the entire 7.3-kDa PPDK chloroplast transit peptide is encoded in the 436-bp first exon. Northern blot experiments with probes specific for the first exon and the 3' end of the gene showed that the smaller PPDK transcripts in roots and etiolated leaves [3.0 kilobases (kb) vs. the 3.5-kb green leaf transcript] lack the sequence encoding the chloroplast transit peptide. In addition, results from cDNA library screens have confirmed that the root transcript is approximately 50-fold less abundant than the green leaf transcript. Finally, sequence comparisons among cDNA clones from green leaves and roots and genomic clones representing both members of the PPDK gene family demonstrate that the green leaf transcript encoding the C4 isozyme and the root transcript are derived from the same gene. (+info)
Structure, genetic mapping, and expression of the gene for pyruvate, orthophosphate dikinase from maize.
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Pyruvate, orthophosphate dikinase is a key enzyme in photosynthesis in some plants that exploit the C4 photosynthetic pathway for the fixation of CO2. The gene for this enzyme has been cloned and its primary structure has been analyzed. The sequence of the cloned genes spans about 12 kilobase pairs and consists of 19 exons. The site of initiation of transcription is located 211 nucleotides upstream from the first nucleotide of the initiation codon (position -211). Typical TATA and inverted CCAAT elements are present in the anticipated regions, as well as a sequence that is homologous to the binding site of Sp-1 protein (-51 to -42). Three long, direct-repeated sequences are present contiguously in the 5'-flanking region (-286 to -172), and two of the repeated sequences include sequences homologous to the core sequence of SV40 enhancer in the 3'-end portions. Southern blot analysis, coupled with mapping by analysis of restriction fragment length polymorphism, indicates that the gene for the enzyme involved in C4 photosynthesis is encoded by a single-copy gene and is located on chromosome 6. To test the promoter activity of the isolated gene, a chimeric gene composed of the 5'-flanking region of the gene and a structural gene for bacterial beta-glucuronidase was constructed and introduced into tobacco protoplasts by electroporation or used to transform tobacco plants by Agrobacterium-mediated transfer of the gene. In both cases, expression of the beta-glucuronidase gene was observed, indicating that the 5'-flanking region of the gene can act as a promoter in tobacco cells. (+info)