Molecular characterization and expression of a cDNA encoding copper/zinc superoxide dismutase from cultured cells of cassava (Manihot esculenta Crantz)

Overexpression of alfalfa mitochondrial HSP23 in prokaryotic and eukaryotic model systems confers enhanced tolerance to salinity and arsenic stress

The cloning and characterization of a gene (MsHSP23) coding for a heat shock protein in alfalfa in a prokaryotic and model plant system is described. MsHSP23 contains a 633 bp ORF encoding a polypeptide of 213 amino acids and exhibits greater sequence similarity to mitochondrial sHSPs from dicotyledons than to those from monocotyledons. When expressed in bacteria, recombinant MsHSP23 conferred tolerance to salinity and arsenic stress. Furthermore, MsHSP23 was cloned in a plant expressing vector and transformed into tobacco, a eukaryotic model organism. The transgenic plants exhibited enhanced tolerance to salinity and arsenic stress under ex vitro conditions. In comparison to wild type plants, the transgenic plants exhibited significantly lower electrolyte leakage. Moreover, the transgenic plants had superior germination rates when placed on medium containing arsenic. Taken together, these overexpression results imply that MsHSP23 plays an important role in salinity and arsenic stress tolerance in transgenic tobacco. This approach could be useful to develop stress tolerant crops including forage crops.

Differential expression of copper-zinc superoxide dismutase gene of Polygonum sibiricum leaves, stems and underground stems, subjected to high-salt stress

In aerobic organisms, protection against oxidative damage involves the combined action of highly specialized antioxidant enzymes, such as copper-zinc superoxide dismutase. In this work, a cDNA clone which encodes a copper-zinc superoxide dismutase gene, named PS-CuZnSOD, has been identified from P. sibiricum Laxm. by the rapid amplification of cDNA ends method (RACE). Analysis of the nucleotide sequence reveals that the PS-CuZnSOD gene cDNA clone consists of 669 bp, containing 87 bp in the 5′ untranslated region; 459 bp in the open reading frame (ORF) encoding 152 amino acids; and 123 bp in 3′ untranslated region. The gene accession nucleotide sequence number in GenBank is GQ472846. Sequence analysis indicates that the protein, like most plant superoxide dismutases (SOD), includes two conserved ecCuZnSOD signatures that are from the amino acids 43 to 51, and from the amino acids 137 to 148, and it has a signal peptide extension in the front of the N-terminus (1–16 aa). Expression analysis by real-time quantitative PCR reveals that the PS-CuZnSOD gene is expressed in leaves, stems and underground stems. PS-CuZnSOD gene expression can be induced by 3% NaHCO₃. The different mRNA levels’ expression of PS-CuZnSOD show the gene’s different expression modes in leaves, stems and underground stems under the salinity-alkalinity stress.

Enhanced tolerance of transgenic potato plants expressing both superoxide dismutase and ascorbate peroxidase in chloroplasts against oxidative stress and high temperature

Oxidative stress is a major damaging factor for plants exposed to environmental stresses. In order to develop transgenic potato plants with enhanced tolerance to environmental stress, the genes of both Cu/Zn superoxide dismutase and ascorbate peroxidase were expressed in chloroplasts under the control of an oxidative stress-inducible SWPA2 promoter (referred to as SSA plants). SSA plants showed enhanced tolerance to 250 microM methyl viologen, and visible damage in SSA plants was one-fourth that of non-transgenic (NT) plants that were almost destroyed. In addition, when SSA plants were treated with a high temperature of 42 degrees C for 20 h, the photosynthetic activity of SSA plants decreased by only 6%, whereas that of NT plants decreased by 29%. These results suggest that the manipulation of the antioxidative mechanism of the chloroplasts may be applied in the development of industrial transgenic crop plants with increased tolerance to multiple environmental stresses.

Molecular cloning of a cytosolic ascorbate peroxidase cDNA from cell cultures of sweet potato and its expression in response to stress

A cDNA encoding a cytosolic ascorbate peroxidase (APX), swAPX1, was isolated from cell cultures of sweet potato ( Ipomoea batatas) by cDNA library screening, and its expression in the context of various environmental stresses was investigated. swAPX1 contains an ORF of 250 amino acids (27.5 kDa) encoding a protein with a pI value of 5.32. The swAPX1 ORF does not code for a transit peptide, suggesting that the product is a cytosolic isoform. RNA blot analysis showed that swAPX1 gene is expressed in cultured cells and mature leaves, but not in stems, non-storage or storage roots of sweet potato. The level of swAPX1 RNA progressively increased during cell growth in suspension cultures. In leaf tissues, the gene responded differentially to various abiotic stresses, as revealed by RT-PCR analysis. swAPX1 was highly induced in leaves by wounding, and treatment with methyl viologen (50 microM), hydrogen peroxide (440 mM), abscisic acid (ABA; 100 microM) or exposure to high temperature (37 degrees C). In addition, the gene was strongly induced in the leaves following inoculation with a bacterial pathogen ( Pectobacterium chrysanthemi). These results indicate that swAPX1 may be involved in hydrogen peroxide-detoxification and thus help to overcome the oxidative stress induced by abiotic and biotic stresses.

Differential expression of six novel peroxidase cDNAs from cell cultures of sweetpotato in response to stress

Six peroxidase (POD) cDNAs were isolated from suspension cultures of sweetpotato (Ipomoea batatas) by cDNA library screening, and their expression was investigated with a view to understanding the physiological functions of each POD in relation to environmental stress. The gene products encoded by these cDNAs could be divided into two groups, anionic PODs (SWPA4, SWPA5, SWPA6) and basic PODs (SWPB1, SWPB2, SWPB3), on the basis of the predicted pI values of the mature proteins. RT-PCR analysis revealed that the six POD genes showed diverse expression patterns in various tissues of intact plants, a various stages of growth in suspension cultures, and in leaf tissues exposed to different stresses. The six genes from which they were derived are predominantly expressed in cultured cells of sweetpotato. Thus, transcripts of swpa4 were not detected in any tissues of the intact plant. The genes swpa6 and swpb1 were highly expressed in root tissues, whereas swpa6 and swpb3 were highly expressed in stem tissues. During suspension culture, the expression patterns of the six genes differed from each other. The level of swpa4, swpa5, swpb2 and swpb3 transcripts progressively increased during culture, whereas swpa6 and swpb1 showed high expression levels regardless of the age of the culture. In leaf tissues the six POD genes responded differently to various abiotic stresses. In particular, swpa4 was highly induced by several abiotic stresses, including exposure to hydrogen peroxide (440 mM) or NaCl (100 mM), and wounding of leaf tissues, suggesting that this POD gene is inducible by many stresses. Based on the different expression patterns of these POD genes, we propose that each POD may have different enzymatic properties and physiological functions during cell growth and development.