Temporal pattern of jasmonate-induced alterations in gene expression of barley leaves

The role of dysregulated mRNA translation machinery in cancer pathogenesis and therapeutic value of ribosome-inactivating proteins

Dysregulated protein synthesis is a hallmark of tumors. mRNA translation reprogramming contributes to tumorigenesis, which is fueled by abnormalities in ribosome formation, tRNA abundance and modification, and translation factors. Not only malignant cells but also stromal cells within tumor microenvironment can undergo transformation toward tumorigenic phenotypes during translational reprogramming. Ribosome-inactivating proteins (RIPs) have garnered interests for their ability to selectively inhibit protein synthesis and suppress tumor growth. This review summarizes the role of dysregulated translation machinery in tumor development and explores the potential of RIPs in cancer treatment.

Comparative Physiological and Proteomic Analysis of Two Sugar Beet Genotypes with Contrasting Salt Tolerance

Soil salinity is one of the major constraints affecting agricultural production and crop yield. A detailed understanding of the underlying physiological and molecular mechanisms of the different genotypic salt tolerance response in crops under salinity is therefore a prerequisite for enhancing this tolerance. In this study, we explored the changes in physiological and proteome profiles of salt-sensitive (S210) and salt-tolerant (T510) sugar beet cultivars in response to salt stress. T510 showed better growth status, higher antioxidant enzymes activities and proline level, less Na accumulation, and lower P levels after salt-stress treatments. With iTRAQ-based comparative proteomics method, 47 and 56 differentially expressed proteins were identified in the roots and leaves of S210, respectively. In T510, 56 and 50 proteins changed significantly in the roots and leaves of T510, respectively. These proteins were found to be involved in multiple aspects of functions such as photosynthesis, metabolism, stress and defense, protein synthesis, and signal transduction. Our proteome results indicated that sensitive and tolerant sugar beet cultivars respond differently to salt stress. The proteins that were mapped to the protein modification, amino acid metabolism, tricarboxylic acid cycle, cell wall synthesis, and reactive oxygen species scavenging changed differently between the sensitive and tolerant cultivars, suggesting that these pathways may promote salt tolerance in the latter. This work leads to a better understanding of the salinity mechanism in sugar beet and provides a list of potential markers for the further engineering of salt tolerance in crops.

Methyl jasmonate, gibberellic acid, and auxin affect transcription and transcript accumulation of chloroplast genes in barley

Phytohormones control growth and development of plants. Their effects on the expression of nuclear genes are well investigated. Although they influence plastid-related processes, it is largely unknown whether phytohormones exert their control also by regulating the expression of plastid/chloroplast genes. We have therefore studied the effects of methyl jasmonate (MeJA), gibberellic acid (GA(3)), an auxin (indole-3-acetic acid, IAA), a brassinosteroid (24-epibrassinolide, BR) and a cytokinin (6-benzyladenine) on transcription (run-on assays) and transcript levels (RNA blot hybridization) of chloroplast genes after incubation of detached barley leaves in hormone solutions. BR was the only hormone without significant influence on chloroplast transcription. It showed, however, a weak reducing effect on transcript accumulation. MeJA, IAA and GA(3) repressed both transcription and transcript accumulation, while BA counteracted the effects of the other hormones. Effects of phytohormones on transcription differed in several cases from their influence on transcript levels suggesting that hormones may act via separate signaling pathways on transcription and transcript accumulation in chloroplasts. We observed striking differences in the response of chloroplast gene expression on phytohormones between the lower (young cells) and the upper segments (oldest cells) of barley leaves. Quantity and quality of the hormone effects on chloroplast gene expression seem to depend therefore on the age and/or developmental stage of the cells. As the individual chloroplast genes responded in different ways on phytohormone treatment, gene- and transcript-specific factors should be involved. Our data suggest that phytohormones adjust gene expression in the nucleo-cytoplasmic compartment and in plastids/chloroplasts in response to internal and external cues.

The role of Arabidopsis Rubisco activase in jasmonate-induced leaf senescence

Leaf senescence, as the last stage of leaf development, is regulated by diverse developmental and environmental factors. Jasmonates (JAs) have been shown to induce leaf senescence in several plant species; however, the molecular mechanism for JA-induced leaf senescence remains unknown. In this study, proteomic, genetic, and physiological approaches were used to reveal the molecular basis of JA-induced leaf senescence in Arabidopsis (Arabidopsis thaliana). We identified 35 coronatine-insensitive 1 (COI1)-dependent JA-regulated proteins using two-dimensional difference gel electrophoresis in Arabidopsis. Among these 35 proteins, Rubisco activase (RCA) was a COI1-dependent JA-repressed protein. We found that RCA was down-regulated at the levels of transcript and protein abundance by JA in a COI1-dependent manner. We further found that loss of RCA led to typical senescence-associated features and that the COI1-dependent JA repression of RCA played an important role in JA-induced leaf senescence.

Histological and molecular analysis of Rdg2a barley resistance to leaf stripe

Barley (Hordeum vulgare L.) leaf stripe is caused by the seed-borne fungus Pyrenophora graminea. We investigated microscopically and molecularly the reaction of barley embryos to leaf stripe inoculation. In the resistant genotype NIL3876-Rdg2a, fungal growth ceased at the scutellar node of the embryo, while in the susceptible near-isogenic line (NIL) Mirco-rdg2a fungal growth continued past the scutellar node and into the embryo. Pathogen-challenged embryos of resistant and susceptible NILs showed different levels of UV autofluorescence and toluidine blue staining, indicating differential accumulation of phenolic compounds. Suppression subtractive hybridization and cDNA amplified fragment-length polymorphism (AFLP) analyses of embryos identified P. graminea-induced and P. graminea-repressed barley genes. In addition, cDNA-AFLP analysis identified six pathogenicity-associated fungal genes expressed during barley infection but at low to undetectable levels during growth on artificial media. Microarrays representing the entire set of differentially expressed cDNA-AFLP fragments and 100 barley homologues of previously described defence-related genes were used to study gene expression changes at 7 and 14 days after inoculation in the resistant and susceptible NILs. A total of 171 significantly modulated barley genes were identified and assigned to four groups based on timing and genotype dependence of expression. Analysis of the changes in gene expression during the barley resistance response to leaf stripe suggests that the Rdg2a-mediated response includes cell-wall reinforcement, signal transduction, generation of reactive oxygen species, cell protection, jasmonate signalling and expression of plant effector genes. The identification of genes showing leaf stripe inoculation or resistance-dependent expression sets the stage for further dissection of the resistance response of barley embryo cells to leaf stripe.

Methyl jasmonate is a more effective senescence-promoting factor in Cucurbita pepo (zucchini) cotyledons when compared with darkness at the early stage of senescence

The effects of short-term darkening and methyl jasmonate (MeJA) on cotyledon senescence were studied 24h after transfer of intact 7-day-old Cucurbita pepo (zucchini) seedlings to darkness or spraying with 100 microM MeJA. The jasmonate inhibitory effect on chlorophyll content and chloroplast transcriptional activity was stronger compared with darkness. Further, MeJA reduced the photosynthetic rate whereas darkness did not affect photosynthesis. Neither stress factor affected the photochemical quantum efficiency of photosystem II (PSII) estimated by the variable fluorescence (F(v))/maximal fluorescence (F(m)) ratio, suggesting the existence of mechanisms protecting the functional activity of PSII at earlier stages of senescence, thus making this parameter more stable compared to others used to quantify senescence. Both stress factors caused a decrease in the content of physiologically active cytokinins, especially trans-zeatin (Z), with the jasmonate effect being much more pronounced when compared to darkness. Our results indicate that MeJA is a more potent inducer of senescence in zucchini cotyledons, at least within the relatively short period of the 24h treatment. This is likely due to its stronger down-regulatory effect on the levels of physiologically active cytokinins.

Antioxidants in photosynthesis and human nutrition

The harnessing of solar energy by photosynthesis depends on a safety valve that effectively eliminates hazardous excess energy and prevents oxidative damage to the plant cells. Many of the compounds that protect plant cells also protect human cells. Improving plant resistance to stress may thus have the beneficial side effect of also improving the nutritional quality of plants in the human diet. The pathways that synthesize these compounds are becoming amenable to genetic manipulation, which may yield benefits as widespread as improved plant stress tolerance and improved human physical and mental health.

Jasmonates and octadecanoids: signals in plant stress responses and development

Plants are sessile organisms. Consequently they have to adapt constantly to fluctuations in the environment. Some of these changes involve essential factors such as nutrients, light, and water. Plants have evolved independent systems to sense nutrients such as phosphate and nitrogen. However, many of the environmental factors may reach levels which represent stress for the plant. The fluctuations can range between moderate and unfavorable, and the factors can be of biotic or abiotic origin. Among the biotic factors influencing plant life are pathogens and herbivores. In case of bacteria and fungi, symbiotic interactions such as nitrogen-fixating nodules and mycorrhiza, respectively, may be established. In case of insects, a tritrophic interaction of herbivores, carnivores, and plants may occur mutualistically or parasitically. Among the numerous abiotic factors are low temperature, frost, heat, high light conditions, ultraviolet light, darkness, oxidation stress, hypoxia, wind, touch, nutrient imbalance, salt stress, osmotic adjustment, water deficit, and desiccation. In the last decade jasmonates were recognized as being signals in plant responses to most of these biotic and abiotic factors. Signaling via jasmonates was found to occur intracellularly, intercellularly, and systemically as well as interorganismically. Jasmonates are a group of ubiquitously occurring plant growth regulators originally found as the major constituents in the etheric oil of jasmine, and were first suggested to play a role in senescence due to a strong senescence-promoting effect. Subsequently, numerous developmental processes were described in which jasmonates exhibited hormone-like properties. Recent knowledge is reviewed here on jasmonates and their precursors, the octadecanoids. After discussing occurrence and biosynthesis, emphasis is placed upon the signal transduction pathways in plant stress responses in which jasmonates act as a signal. Finally, examples are described on the role of jasmonates in developmental processes.

Isolation and characterization of a novel ribosome-inactivating protein from root cultures of pokeweed and its mechanism of secretion from roots

Ribosome-inactivating proteins are N-glycosidases that remove a specific adenine from the sarcin/ricin loop of the large rRNA, thus arresting protein synthesis at the translocation step. In the present study, a novel type I ribosome-inactivating protein, termed PAP-H, was purified from Agrobacterium rhizogenes-transformed hairy roots of pokeweed (Phytolacca americana). The protein was purified by anion- and cation-exchange chromatography. PAP-H has a molecular mass of 29.5 kD as detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and its isoelectric point was determined to be 7.8. Yeast (Saccharomyces cerevisiae) ribosomes incubated with PAP-H released the 360-nucleotide diagnostic fragment from the 26S rRNA upon aniline treatment, an indication of its ribosome-inactivating activity. Using immunofluorescence microscopy, PAP-H was found to be located in the cell walls of hairy roots and root border cells. PAP-H was determined to be constitutively secreted as part of the root exudates, with its secretion enhanced by a mechanism mediated by ethylene induction. Purified PAP-H did not show in vitro antifungal activity against soil-borne fungi. In contrast, root exudates containing PAP-H as well as additional chitinase, beta-1,3-glucanase, and protease activities did inhibit the growth of soil-borne fungi. We found that PAP-H depurinates fungal ribosomes in vitro and in vivo, suggesting an additive mechanism that enables PAP-H to penetrate fungal cells.

Biochemical evaluation of lipoxygenase pathway of soybean plants submitted to wounding

Leaf lipoxygenases (LOX) are involved with important physiological processes such as plant growth and development, senescence, biosynthesis of regulatory molecules, and response to pathogens and insects. We did a biochemical evaluation of the LOX pathway of soybean leaves submitted to wounding in a normal genotype (IAC-100) and its counterpart lacking seed LOX (IAC-100 TN). Our results indicate that LOX activities in the different pHs and temperatures tended to be higher in the wounded plants compared to their respective controls. The K M app values at 168 h after wounding reached a minimum in both genotypes indicating that the plants respond by changing the leaf LOX pool. There was an increase on protease inhibitor levels in all time points after wounding, for both cultivars. The levels of hexanal and total aldehydes are similar for the wounded plants at different times after wounding and their respective controls for both genotypes. Our results strongly suggest that the LOX pathway is activated during the wound response leading to jasmonate by the initial action of hydroperoxide cyclase. In addition, the results show that the genetic removal of seed LOX does not interfere with the plant’s ability to respond to wound via the LOX pathway.

Differential effects of methyl jasmonate on the expression of the early light-inducible proteins and other light-regulated genes in barley

The effects of methyl jasmonate (JA-Me) on early light-inducible protein (ELIP) expression in barley (Hordeum vulgare L. cv Apex) have been studied. Treatment of leaf segments with JA-Me induces the same symptoms as those exhibited by norflurazon bleaching, including a loss of pigments and enhanced light stress that results in increased ELIP expression under both high- and low-light conditions. The expression of both low- and high-molecular-mass ELIP families is considerably down-regulated by JA-Me at the transcript and protein levels. This repression occurs despite increased photoinhibition measurable as a massive degradation of D1 protein and a delayed recovery of photosystem II activity. In JA-Me-treated leaf segments, the decrease of the photochemical efficiency of photosystem II under high light is substantially more pronounced as compared to controls in water. The repression of ELIP expression by JA-Me is superimposed on the effect of the increased light stress that leads to enhanced ELIP expression. The fact that the reduction of ELIP transcript levels is less pronounced than those of light-harvesting complex II and small subunit of Rubisco transcripts indicates that light stress is still affecting gene expression in the presence of JA-Me. The jasmonate-induced protein transcript levels that are induced by JA-Me decline under light stress conditions.

Overexpression of the jasmonate-inducible 23 kDa protein (JIP 23) from barley in transgenic tobacco leads to the repression of leaf proteins

We investigated transgenic tobacco lines which express different amounts of the barley JIP 23. In these plants the amount of several proteins decreased proportionally to increasing amounts of JIP 23 whereas the transcript levels were constant as determined for the small and the large subunit of RuBPCase. However, the translation initiation of the rbcS transcript was found to be less efficient than in the wild type. In contrast, the jip 23 transcript was efficiently initiated, indicating that no unspecific impairment of initiation occurred. The data suggest that the barley JIP 23 leads to discrimination among certain tobacco transcripts during translation initiation.