Cloning and biochemical characterization of an anionic peroxidase from Zea mays

Cloning and functional analysis of the promoter of a stress-inducible gene (Zmap) in maize

The anionic peroxidases play an important role in a variety of plant physiological processes. We characterized and isolated the Zmap promoter (PZmap) at the 5' flanking region in order to better understand the regulatory mechanisms of Zmap gene expression. A series of PZmap deletion derivatives, termed a1 -a6, at positions -1694, -1394, -1138, -784, -527 and -221 from the translation start site were blended to the β-glucuronidase reporter gene. Agrobacterium-mediated transformation method was used to study each deletion construct in tobaccos. Sequence analysis showed that several cis-acting elements (MYB binding site, Box-II, a TGACG-element, a CGTCA-element and a low temperature responsive element) were located within the promoter. Deletion analysis suggested the sequence between -1,694 and -1394bp may contain cis-elements associated with GUS up regulation. The MYB binding site (-757) might act as a negative drought-responsive element. There might be repressor elements located in the region (-1,694 to -1394bp) to repress Zmap expression under 4°C. The characterized promoter would be an ideal candidate for genetic engineering for improving the resistance of maize to different stressors.

Cationic peroxidase from proso millet induces human colon cancer cell necroptosis by regulating autocrine TNF-α and RIPK3 demethylation

A cationic peroxidase (POD) was purified from proso millet seeds (PmPOD) using ammonium sulfate fractionation, cation exchange, and size exclusion chromatography. The purified PmPOD showed toxicity to normal cells and tumor cells, but was more sensitive in HT29 cells. Furthermore, the mechanism driving HCT116 and HT29 cell death by PmPOD was the induction of receptor interacting protein kinase 1 (RIPK1)- and RIPK3-dependent necroptosis, independent of apoptosis. More importantly, PmPOD could induce tumor necrosis factor-α (TNF-α) production through transcriptional upregulation. In addition, PmPOD could restore RIPK3 expression in HCT116 cells via the demethylation of the RIPK3 genomic sequence. Taken together, these results suggest that two distinct mechanisms are involved in PmPOD-induced necroptosis: the autocrine production of TNF-α and the restoration of RIPK3 expression.

Identification and properties of insect resistance-associated maize anionic peroxidases

Previous studies with transgenic plants have indicated a tobacco anionic peroxidase can confer enhanced resistance to a variety of insects when expressed in different plant species. Tissue that expresses high levels of this enzyme often browns rapidly when damaged. Maize roots damaged under sterile conditions browned and had an anionic peroxidase induced. When introduced biolistically, maize callus transformants expressing a maize peroxidase gene with a predicted isoelectric point of ca. 5.1 produced browner callus compared to a corresponding beta-glucuronidase (GUS) transformant as callus aged. Higher production of only one isozyme of ca. pI 4.5 was noted. When the callus was fed to two maize pest caterpillar species, growth rates were slower (as reflected by weights) relative to the GUS callus. Based on examination of published information and electrophoretic properties, this gene appears to code for Px11, a peroxidase isozyme that is primarily produced in root tissue and callus. When sequence of the gene in several inbreds was examined, coding variations were noted, and abilities to utilize ferulic and p-coumaric acids differed. These coding differences may influence the ability of corresponding forms of the peroxidase to promote resistance. In addition to potential use in marker assisted breeding, enhanced expression of this anionic peroxidase through breeding or genetic engineering may lead to enhanced insect or disease resistance.

Biochemical characterization of the major sorghum grain peroxidase

The major cationic peroxidase in sorghum grain (SPC4) , which is ubiquitously present in all sorghum varieties was purified to apparent homogeneity, and found to be a highly basic protein (pI approximately 11). MS analysis showed that SPC4 consists of two glycoforms with molecular masses of 34,227 and 35,629 Da and it contains a type-b heme. Chemical deglycosylation allowed to estimate sugar contents of 3.0% and 6.7% (w/w) in glycoform I and II, respectively, and a mass of the apoprotein of 33,246 Da. High performance anion exchange chromatography allowed to determine the carbohydrate constituents of the polysaccharide chains. The N-terminal sequence of SPC4 is not blocked by pyroglutamate. MS analysis showed that six peptides, including the N-terminal sequence of SPC4 matched with the predicted tryptic peptides of gene indice TC102191 of sorghum chromosome 1, indicating that TC102191 codes for the N-terminal part of the sequence of SPC4, including a signal peptide of 31 amino acids. The N-terminal fragment of SPC4 (213 amino acids) has a high sequence identity with barley BP1 (85%), rice Prx23 (90%), wheat WSP1 (82%) and maize peroxidase (58%), indicative for a common ancestor. SPC4 is activated by calcium ions. Ca2+ binding increased the protein conformational stability by raising the melting temperature (Tm) from 67 to 82 degrees C. SPC4 catalyzed the oxidation of a wide range of aromatic substrates, being catalytically more efficient with hydroxycinnamates than with tyrosine derivatives. In spite of the conserved active sites, SPC4 differs from BP1 in being active with aromatic compounds above pH 5.

Association of a specific cationic peroxidase isozyme with maize stress and disease resistance responses, genetic identification, and identification of a cDNA coding for the isozyme

The presence of a pI 9.0 cationic peroxidase isozyme from milk stage pericarp of six susceptible and five resistant inbreds was correlated significantly with previously reported field data on percentage infection by Aspergillus flavus in the inbreds and their hybrids. The isozyme was constitutively expressed in some additional maize tissues and lines examined, and frequently induced by mechanical damage, heat shock, Fusarium proliferatum, and/or Bacillus subtilis in other lines tested. Native/IEF two-dimensional electrophoresis identified the isozyme as the previously genetically identified px5. A cDNA clone expressed in black Mexican sweet (BMS) maize cell cultures produced the pI 9.0 isozyme. In addition to potential use in marker-assisted breeding, enhanced expression of this cationic peroxidase through breeding or genetic engineering may lead to enhanced disease or insect resistance.

Characterisation of maize peroxidases having differential patterns of mRNA accumulation in relation to lignifying tissues

Among other enzymes, peroxidases have been proposed to participate in the latest steps of lignin biosynthesis. In order to identify new proteins involved in such mechanism of lignification in maize, we have isolated three cDNAs coding for three different peroxidases, named ZmPox1, ZmPox2, and ZmPox3, respectively. Computational analyses of these three proteins correlate with features typically attributed to heme-containing plant peroxidases of approximately 300 amino acid residues. Although with different expression levels, ZmPox2 and ZmPox3 mRNAs are accumulated in the elongating region of young roots but not in the root tips. In addition, the ZmPox2 mRNA levels are up-regulated by wounding and ethylene treatments. However, ZmPox1 is also expressed in the root tip meristems, where lignification does not occur. Finally, in situ hybridisations indicate that ZmPox2 mRNA localises in vascular tissues and epidermis. Although ZmPox1 mRNA localises in the same regions as ZmPox2 mRNA in root tips, its mRNA is only detected in the epidermis but not in the vascular tissues of young roots, suggesting that the function of ZmPox1 is not correlated to lignification. In addition, although ZmPox3 mRNA is also detected in the regions where lignification occurs, the involvement of this peroxidase in such a mechanism remains to be further investigated due to its very low expression level. Therefore, based on its amino acid sequence and mRNA accumulation and localisation patterns, the involvement of ZmPox2 in the latest steps of lignification is discussed.

Purification and characterization of a peroxidase from corn steep water

Three cationic peroxidases have been detected in early, middle, and late corn steep water, with pI values of approximately 8.9, approximately 9.5, and >10.0. The major cationic corn steep water peroxidase (CSWP), with a pI >10, was purified 36400-fold with a 12% recovery from late steep water by a combination of acetone and ammonium sulfate precipitation and sequential chromatography on CM-cellulose, phenyl-Sepharose, and Sephadex G-75. The UV-vis spectrum of purified CSWP is typical of other plant class III peroxidases. The RZ (A(403)/A(280)) of CSWP was between 2.6 and 2.9. It is not glycosylated and exhibited an M(r) of 30662 +/- 7 by MALDI-TOF MS. The pH optimum of CSWP depends on the substrate, and it is active on 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), guaiacol, ferulic acid, o-dianisidine, o-phenylenediamine, and pyrogallol but is not active on either syringaldazine or ascorbate. At 75 degrees C and pH 4.5, the enzyme has half-lives of 22.7 min (0 mM Ca(2+)) and 248 min (1 mM Ca(2+)). The enzyme is stable at room temperature (22-25 degrees C), losing <3% of the activity at pH 4.5 and <10% at pH 6.2 over 400 h in the presence of 1 mM Ca(2+).

Molecular cloning and tissue-specific expression of an anionic peroxidase in zucchini

A calcium-pectate-binding anionic isoperoxidase (APRX) from zucchini (Cucurbita pepo) was purified and subjected to N-terminal amino acid microsequencing. The cDNA encoding this enzyme was obtained by reverse transcriptase polymerase chain reaction from a cDNA library. It encoded a mature protein of 309 amino acids exhibiting all of the sequence characteristics of a plant peroxidase. Despite the presence of a C-terminal propeptide, APRX was found in the apoplast. APRX protein and mRNA were found in the root, hypocotyls, and cotyledons. In situ hybridization showed that the APRX-encoding gene was expressed in many different tissues. The strongest expression was observed in root epidermis and in some cells of the stele, in differentiating tracheary elements of hypocotyl, in the lower and upper epidermis, in the palisade parenchyma of cotyledons, and in lateral and adventitious root primordia. In the hypocotyl hook there was an asymmetric expression, with the inner part containing more transcripts than the outer part. Treatment with 2,3,5-triiodobenzoic acid reduced the expression of the APRX-encoding gene in the lower part of the hypocotyl. Our observations suggest that APRX could be involved in lignin formation and that the transcription of its gene was related to auxin level.

Regulation of polar auxin transport by AtPIN1 in Arabidopsis vascular tissue

Polar auxin transport controls multiple developmental processes in plants, including the formation of vascular tissue. Mutations affecting the PIN-FORMED (PIN1) gene diminish polar auxin transport in Arabidopsis thaliana inflorescence axes. The AtPIN1gene was found to encode a 67-kilodalton protein with similarity to bacterial and eukaryotic carrier proteins, and the AtPIN1 protein was detected at the basal end of auxin transport-competent cells in vascular tissue. AtPIN1 may act as a transmembrane component of the auxin efflux carrier.

AtPIN2 defines a locus of Arabidopsis for root gravitropism control

The molecular mechanisms underlying gravity perception and signal transduction which control asymmetric plant growth responses are as yet unknown, but are likely to depend on the directional flux of the plant hormone auxin. We have isolated an Arabidopsis mutant of the AtPIN2 gene using transposon mutagenesis. Roots of the Atpin2::En701 null-mutant were agravitropic and showed altered auxin sensitivity, a phenotype characteristic of the agravitropic wav6-52 mutant. The AtPIN2 gene was mapped to chromosome 5 (115.3 cM) corresponding to the WAV6 locus and subsequent genetic analysis indicated that wav6-52 and Atpin2::En701 were allelic. The AtPIN2 gene consists of nine exons defining an open reading frame of 1944 bp which encodes a 69 kDa protein with 10 putative transmembrane domains interrupted by a central hydrophilic loop. The topology of AtPIN2p was found to be similar to members of the major facilitator superfamily of transport proteins. We have shown that the AtPIN2 gene was expressed in root tips. The AtPIN2 protein was localized in membranes of root cortical and epidermal cells in the meristematic and elongation zones revealing a polar localization. These results suggest that AtPIN2 plays an important role in control of gravitropism regulating the redistribution of auxin from the stele towards the elongation zone of roots.