Wound-induced expression of horseradish peroxidase

Root secretion of defense-related proteins is development-dependent and correlated with flowering time

Proteins found in the root exudates are thought to play a role in the interactions between plants and soil organisms. To gain a better understanding of protein secretion by roots, we conducted a systematic proteomic analysis of the root exudates of Arabidopsis thaliana at different plant developmental stages. In total, we identified 111 proteins secreted by roots, the majority of which were exuded constitutively during all stages of development. However, defense-related proteins such as chitinases, glucanases, myrosinases, and others showed enhanced secretion during flowering. Defense-impaired mutants npr1-1 and NahG showed lower levels of secretion of defense proteins at flowering compared with the wild type. The flowering-defective mutants fca-1, stm-4, and co-1 showed almost undetectable levels of defense proteins in their root exudates at similar time points. In contrast, root secretions of defense-enhanced cpr5-2 mutants showed higher levels of defense proteins. The proteomics data were positively correlated with enzymatic activity assays for defense proteins and with in silico gene expression analysis of genes specifically expressed in roots of Arabidopsis. In conclusion, our results show a clear correlation between defense-related proteins secreted by roots and flowering time.

Differential activity of peroxidase isozymes in response to wounding, gypsy moth, and plant hormones in northern red oak (Quercus rubra L.)

We measured total peroxidase activity and the activities of peroxidase isoforms in leaves of red oak (Quercus rubra L.) seedlings exposed to wounding and plant hormones in the greenhouse. Activity of specific peroxidase isoforms was induced differentially by gypsy moth wounding, mechanical wounding, and the wound-associated plant hormone jasmonic acid. Activity of one isoform was enhanced modestly by treatment with salicylate. A study of peroxidase activity in naturally occurring galls elicited on red oak leaves by 12 hymenopteran and dipteran insect species found 16 POD isoforms, 11 of which were differentially induced or suppressed in galls compared with leaves. In both studies, total peroxidase activity as measured spectrophotometrically was not clearly related to activity of these isoforms. These results indicate that red oak seedlings and trees may respond specifically to wounding, particular insects, and plant signals through changes in the activities of individual isozymes.

Ectopic expression of a horseradish peroxidase enhances growth rate and increases oxidative stress resistance in hybrid aspen

We previously demonstrated that overexpression of the horseradish (Armoracia rusticana) peroxidase prxC1a gene stimulated the growth rate of tobacco (Nicotiana tabacum) plants. Here, the cauliflower mosaic virus 35S::prxC1a construct was introduced into hybrid aspen (Populus sieboldii x Populus grandidentata). The growth rate of these transformed hybrid aspen plants was substantially increased under greenhouse conditions. The average stem length of transformed plants was 25% greater than that of control plants. There was no other obvious phenotypic difference between the transformed and control plants. Fast-growing transformed hybrid aspen showed high levels of expression of prxC1a and had elevated peroxidase activities toward guaiacol and ascorbate. However, there was no increase of the endogenous class I ascorbate peroxidase activities in the transformed plants by separate assay and activity staining of native polyacrylamide gel electrophoresis. Furthermore, calli derived from the transformed hybrid aspen grew faster than those from control plants and were resistant to the oxidative stress imposed by hydrogen peroxide. Therefore, enhanced peroxidase activity affects plant growth rate and oxidative stress resistance.

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.

Transgene expression systems in plant, a natural bioreactor

Plants are important resources that have been providing us food from the earliest times. The rapid advances that have taken place in plant genetic engineering have made it possible to modify plants to increase food production and contribute to environmental purification. Transgenic plants are gaining increasing attention from the industry as a natural bioreactor for the production of industrial and chemical products. Useful expression systems based on promoters to optimize transgene expression in plant cells, hold the key to maximizing the potential of this concept of molecular-farming or industrial plants. This review, which is devoted to the use of plants for heterologous protein production, is divided into three parts. First, we introduce the nature of plant promoters and strategies for the isolation of novel promoters. In the second part, various promoters showing high-level constitutive, organ-specific, or inducible expression, are summarized as useful tools for realizing the efficient transcription of transgenes. Finally, problems in the expression of foreign gene in plant cells and future prospects in plant biotechnology are discussed.

Construction of gene expression system in cultured tobacco cells

To construct a gene expression system in cultured tobacco cells, useful regulatory elements of plant genes were studied. The promoter of the horseradish peroxidase gene, prxC2, showed high activity in tobacco cells, and it contained enhancer sequences and a cis element for wound induction. The heat shock promoter of the HSP18.2 gene from A. thaliana had strong activity of transcription when the incubation temperature of tobacco cells was shifted from 25 degrees C to 37 degrees C. These elements could be good candidates for foreign gene expression in tobacco cells.