01-PlantMolBiol-Cat2 - 913 Isolation characterization and...

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913 Isolation, characterization and expression of the maize Cat2 catalase gene Lingqiang Guan, Alexis N. Polidoros and John G. Scandalios* Department of Genetics, Box 7614. North Cur&m State University, Raleigh, NC 27695-7614, USA i* author for correspondence) Received 19 October 1995; accepted in revised form 22 December 1995 Key words: cat&se, gene expression, gene structure, isozyme, reactive oxygen Abstract The maize Cat2 gene was isolated by direct cloning and PCR. The clones were mapped and sequenced. The start site of transcription was determined by primer extension. Computer analysis of the 1.6 kb Cat2 promoter sequence has revealed an obvious TATA box, two GC boxes, a putative GA response element, and several ACGT core sequences known to have diverse regulatory functions in plants. Several other protein binding motifs were also identified within 800 bp upstream from the transcriptional start site. Five introns were identified in the coding region. All five introns are located in exactly the same position as five of the six introns in Catl, Two of the introns are located in the same position as the two Cat3 introns. The identical positioning of these introns suggests an evolutionary link between all three maize cat&se genes. The response of the gene to plant growth regulators was examined. Results clearly showed that the response of to several environmental factors are developmental stage-dependent. Thus. complex regulatory mechanisms appear to be involved in the regulation of expression in maize. Introduction Catalase (H,0,:H,02 oxidoreductase, EC; CAT) is a tetrameric, heme-containing enzyme found in all aerobic organisms. It pro- vides protection against reactive oxygen toxicity by dismutating hydrogen peroxide to water and oxygen [ 11. In maize (Zea mays L.), three un- linked structural genes, Cal, Cat2, and Cat3 en- code three biochemically distinct isozymes, CAT-l, CAT-Z, and CAT-3 [2,3]. Each of the Cat genes exhibits temporal and spatial specific- ity in its expression [4, 5, 61, and each responds differently to various environmental signals [ 1,7]. In addition, the catalase isozymes exhibit cell and organelle specificities [ 1, and references therein]. For example, CAT-2 first appears during late ker- nel development and increases dramatically in the scutellum after germination. CAT-2 is absent in etiolated leaves, but rapidly accumulates upon ex- posure to light due to increased transcript accu- mulation and translation of the message. The nucleatide sequence data reported will appear in the EMBL Nucleotide Sequence Database under the accession number 254358.
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914 Thus, unlike Cat2 which does not respond to light and Cat3 which is controlled by a circadian clock, Cat2 is positively regulated by light in a tissue- specific manner [ 1, 81. In order to understand the underlying mecha- nisms by which the Cat genes are regulated and expressed in response to various signals, their cDNAs were isolated and used, in turn, to isolate the respective genes. The Cat1 and Cat3 genes were successfully isolated from a genomic library and fully characterized [9, lo]. The Cat2 gene
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01-PlantMolBiol-Cat2 - 913 Isolation characterization and...

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