Constitutive expression of the neutral PR-5 (OLP, PR-5d) gene in roots and cultured cells of tobacco is mediated by ethylene-responsive cis-element AGCCGCC sequences

Genome-wide AP2/ERF gene family analysis reveals the classification, structure, expression profiles and potential function in orchardgrass (Dactylis glomerata)

The AP2/ERF transcription factor (TF) family is of great importance in developmental regulation and responses to stress and pathogenic stimuli. Orchardgrass (Dactylis glomerata), a perennial cold-season forage of high quality in the world's temperate zones, contributes to grazing land through mixed sowing with alfalfa (Medicago sativa) and white clover (Trifolium repens). However, little is known about AP2/ERF TFs in orchardgrass. In this study, 193 AP2/ERF genes were classified into five subfamilies and 13 subgroups through phylogenetic analysis. Chromosome structure analysis showed that AP2/ERF family genes in orchardgrass were distributed on seven chromosomes and specific conservative sequences were found in each subgroup. Exon-intron structure and motifs in the same subgroup were almost identical, and the unique motifs contributed to the classification and functional annotation of DgERFs. Expression analysis showed tissue-specific expression of DgERFs in roots and flowers, with most DgERFs widely expressed in roots. The expression levels of each subgroup (subgroups Vc, VIIa, VIIIb, IXa, and XIa) were high at the before-heading and heading stages (BH_DON and H_DON). In addition, 12 DgERFs in various tissues and five DgERFs associated with abiotic stresses were selected for qRT-PCR analysis showed that four dehydration-responsive element binding (DREB) genes and one ERF subfamily gene in orchardgrass were regulated with PEG, heat and salt stresses. DgERF056 belonged to ERF subfamily was involved in the processes of flowering and development stage. This study systematic explored the DgERFs at the genome level for the first time, which lays a foundation for a better understanding of AP2/ERF gene function in Dactylis glomerata and other types of forage.

Identification and functional characterization of HbOsmotin from Hevea brasiliensis

Latex in the laticiferous cell network of Hevea brasiliensis tree is composed of cytoplasm that synthesizes natural rubber. Ethylene stimulation of the tree bark enhances latex production partly by prolonging the duration of latex flow during the tapping process. Here, we identified an osmotin-like cDNA sequence (HbOsmotin) from H. brasiliensis that belongs to the pathogenesis-related 5 (PR-5) gene family. The HbOsmotin protein is present in the lutoids of latex in H. brasiliensis, whereas in onion epidermal cells, this protein is predominantly distributed around the cell wall, suggesting that it may be secreted from the cytoplasm. We investigated the effects of exogenous ethylene on HbOsmotin transcription and protein accumulation in rubber latex, and further determined the protein function after osmotic stress in Arabidopsis. In regularly tapped trees, HbOsmotin expression was drastically inhibited in rubber latex after tapping, although the expression was subsequently recovered by ethylene stimulation. However, in virgin plants that had never been tapped, exogenous ethylene application slightly decreased HbOsmotin expression. HbOsmotin overexpression in Arabidopsis showed that HbOsmotin reduced the osmotic stress tolerance of the plant, which likely occurred by raising the water potential. These data indicated that HbOsmotin may contribute to osmotic regulation in laticiferous cells.

Osmotin: a plant sentinel and a possible agonist of mammalian adiponectin

Osmotin is a stress responsive antifungal protein belonging to the pathogenesis-related (PR)-5 family that confers tolerance to both biotic and abiotic stresses in plants. Protective efforts of osmotin in plants range from high temperature to cold and salt to drought. It lyses the plasma membrane of the pathogens. It is widely distributed in fruits and vegetables. It is a differentially expressed and developmentally regulated protein that protects the cells from osmotic stress and invading pathogens as well, by structural or metabolic alterations. During stress conditions, osmotin helps in the accumulation of the osmolyte proline, which quenches reactive oxygen species and free radicals. Osmotin expression results in the accumulation of storage reserves and increases the shelf-life of fruits. It binds to a seven-transmembrane-domain receptor-like protein and induces programmed cell death in Saccharomyces cerevisiae through RAS2/cAMP signaling pathway. Adiponectin, produced in adipose tissues of mammals, is an insulin-sensitizing hormone. Strangely, osmotin acts like the mammalian hormone adiponectin in various in vitro and in vivo models. Adiponectin and osmotin, the two receptor binding proteins do not share sequence similarity at the amino acid level, but interestingly they have a similar structural and functional properties. In experimental mice, adiponectin inhibits endothelial cell proliferation and migration, primary tumor growth, and reduces atherosclerosis. This retrospective work examines the vital role of osmotin in plant defense and as a potential targeted therapeutic drug for humans.

Characterization of plant functions using cultured plant cells, and biotechnological applications

Plant cell cultures are widely used in the micro-propagation of clonal plants, especially virus-free plants, and in the production of useful metabolites such as paclitaxel. On the other hand, the use of plant cell cultures for the more basic characterization of plant functions is rather limited due to the difficulties associated with functional differentiation in cell cultures. In this review, I overview our experience with functionally differentiated cultured plant cells and their characteristics, especially with regard to photoautotrophism and secondary metabolism. I emphasize the high potential of functionally differentiated cell cultures, as well as some of the pitfalls, in the characterization of plant functions and biotechnological applications.

Involvement of HbPIP2;1 and HbTIP1;1 aquaporins in ethylene stimulation of latex yield through regulation of water exchanges between inner liber and latex cells in Hevea brasiliensis

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl(2). In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was up-regulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. Increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow.

Overexpression of the AP2/EREBP transcription factor OPBP1 enhances disease resistance and salt tolerance in tobacco

Osmotin promoter binding protein 1 (OPBP1), an AP2/EREBP-like transcription factor of tobacco (Nicotiana tabacum), was isolated using a yeast one-hybrid system. RNA gel blot analysis indicated that expression of the OPBP1 gene was induced by elicitor cryptogein, NaCl, ethephon, methyl jasmonate, as well as cycloheximide. Transient expression analysis using an OPBP1-eGFP fusion gene in onion epidermal cells revealed that the OPBP1 protein was targeted to the nuclear. Further, electrophoretic mobility shift assays demonstrated that the recombinant OPBP1 protein could bind to an oligonucleotide containing the GCC-box cis element. Transgenic tobacco plants with an over expression of the OPBP1 gene accumulated high levels of PR-1a and PR-5d genes and exhibited enhanced resistance to infection by Pseudomonas syringae pv tabaci and Phytophthora parasitica var nicotianae pathogens. They also exhibited increased tolerance to salt stress. These results suggest that OPBP1 might be a transcriptional regulator capable of regulating expression in sets of stress-related genes.

A thaumatin-like gene from Asparagus officinalis (AoPRT-L) exhibits slow activation following tissue maceration or salicylic acid treatment, suggesting convergent defence-related signalling in monocots

Summary Messenger RNA derived from mechanically separated cells of asparagus has proved to be an enriched source of defence-related transcripts. We describe the characterization of a novel PR-5 gene coding for a secreted protein of neutral pI (AoPRT-L) that is strongly up-regulated following cell isolation or following accelerated tissue ageing caused by tissue maceration, but which is also responsive to salicylic acid, a defence-related signal not normally associated with wound responses. Infection with the necrotizing fungal pathogen Stemphylium vesicarium confirmed the responsiveness of AoPRT-L to pathogen challenge in intact plants. An upstream region of the AoPRT-L gene of less than 500 bp was sufficient to confer SA-inducibility in transgenic tobacco. The expression profile of AoPRT-L in both macerated and pathogen challenged tissue suggested there were complex, convergent signalling mechanisms operating during responses to these different stresses.

A PR-5 gene promoter from Asparagus officinalis (AoPRT-L) is not induced by abiotic stress, but is activated around sites of pathogen challenge and by salicylate in transgenic tobacco

Summary Using a promoter-uidA (AoPRT-L-GUS) construct, we have characterized heterologous expression controlled by an Asparagus officinalis acidic PR-5 gene promoter. The construct was found to be up-regulated following a variety of treatments with the defence signal salicylate. Similarly, AoPRT-L-GUS was induced by the SA mimic benzothiodiazole, however, unlike salicylate, this compound does not appear to be transported through the vasculature. The construct was insensitive to wounding and to the wound signal jasmonate. Pathogen challenge resulted in a restricted zone of expression at and around the infection site. High levels of NaCl or PEG 8000 failed to induce foliar expression, however, mannitol proved to be an effective inducer when applied as a root drench. The oxidants H(2)O(2) and t-butyl hydroperoxide also failed to induce AoPRT-L-GUS expression. Developmental expression of the construct appeared to be limited to leaf axils, sepal tips, a proportion of anthers and a small segment of tissue just below the stigma. Thus, the AoPRT-L promoter exhibits a limited expression profile responding principally to salicylate-related defence signals, and shows very little developmental expression. This suggests that the AoPRT-L promoter may be an ideal choice for contained gene expression.