Full TGIF Record # 134656
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Web URL(s):http://turf.rutgers.edu/research/abstracts/symposium2008.pdf
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Content Type:Abstract or Summary only
Author(s):Zhang, Xin; Tadych, Mariusz; Bergen, Marshall; White, James F.
Author Affiliation:Zhang: Department of Plant Biology and Ecology, Nankai University, Tianjin, China; Tadych, Bergen, and White: Department of Plant Biology and Pathology, Rutgers University, New Brunswick, New Jersey
Title:Are endophyte-produced reactive oxygen species (ROS) responsible for improved fungal disease resistance and environmental stress tolerance in endophyte-enhanced turfgrasses?
Section:Poster presentations
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Meeting Info.:New Brunswick, NJ: January 10-11, 2008
Source:Proceedings of the Seventeenth Annual Rutgers TurfgrassSymposium. 2008, p. 61-63.
Publishing Information:New Brunswick, NJ: Center for Turfgrass Science, Cook College, Rutgers, The State University of New Jersey
# of Pages:3
Keywords:TIC Keywords: Endophytes; Fungi; Disease resistance; Environmental stress; Fine fescues; Biological control organisms; Endophytic fungi; Reactive oxygen species
Abstract/Contents:"Endophytic fungi are an important means to improve performance of many turf species. They are commonly found in cool-season grasses and have been documented to make turfgrasses more resistant to insect feeding, suppress fungus diseases and make grasses more drought and heavy metal tolerant. Research has shown that some endophytic-infected grasses show enhanced resistance to certain fungal diseases of grasses, including red thread and dollar spot diseases (Bonos et al., 2005; Clarke et al., 2006). When challenged by an exogenous invader, plants and animals frequently present defensive reactions of secretion of reactive oxygen species (ROS). Also, some fungi are endowed with the ability to recognize potential competitors and respond by the generation of peroxides, another ROS moiety (Silar, 2005). ROS secretion is the most basic and least costly defensive mechanism exhibited by aerobic organisms. Recently, ROS has been demonstrated to be produced and secreted by a perennial ryegrass endophyte; and ROS was proposed to be critical in maintaining the mutualistic fungus-plant interaction (Tanaka et al., 2006), although details of the mechanism of how ROS secretion by endophytes may explain several phenomena exhibited by endophyte-enhanced grasses, including improved disease resistance and environmental stress tolerance in grasses. In fine fescue grasses, endophytes frequently produce a dense network of mycelium on plant surfaces where endophytes may interact antagonistically with potential pathogens to either prevent disease progression or permit it, depending on the outcome of the endophyte-pathogen interactions. Developing an understanding of the endophyte-enhanced disease resistance phenomenon is the primary target of this particular research project. Initially we conducted a survey of numerous fine fescue plants to identify E+ and E- clone pairs showing differences with respect to how E+ and E- plants respond to internally-generated ROS using the 'diquat dibromide test'. In this test diquat dibromide forces plant cells to generate ROS resulting in clorosis in the plant tissues. Differences between E+ and E- clones would suggest that the endophyte modifies plant response with respect to ROS tolerance. Typically grasses under stress will show a reduced toleranec in this ROS test (becoming clorotic more rapidly); and improved tolerance to ROS in the diquat dibromide test reflects either production of ROS quenching compounds (e.g., proline) by the plant or symbiotic endophyte (e.g., mannitol, trehalose, or other reducing carbohydrate) or may reflect that plants are under reduced stress. When endophyte-infected (E+) and endophyte-free (E-) plants of fine fescue (Festuca rubra) from greenhouse collections were treated with diquat dibromide to examine thier susceptibility to internally-produced, E+ plants of fine fescue clone #33 showed more clorosis due to the production of the internally-produced ROS than E- plants; conversely, fine fescue clone #17 demonstrated the opposite reaction with E+ plants showing more tolerance to internally-produced ROS than E- clones. These two sets of fine fescue clones were selected for further research to determine how the endophytes were modifying tolerance to internally-generated ROS. We propose that differences in the production of ROS (perhaps concentrations) may be responsible for the modification in plant response to internally-generated ROS. If the endophyte from clone #17 is producing and secreting ROS into grass apoplasts, grass cells may be adjusting their tolerance to ROS through secretion of proline (a known ROS-quenching compound previously associated with improved drought and heavy metal tolerance in endophyte-enhanced grasses), essentially resulting in plants that are more resistant to ROS. Conversely, the endophyte of clone #33 may not be secreting ROS, or may be secreting lower concentrations of ROS, which are not stimulating plant cells to adjust tolerance to ROS. The enhanced sensitivity to internally-generated ROS in E+ plants of clone #33 may be due to increased stress on these plants due to presence of the endophyte. To further evaluate ROS production by these endophytes and test their effectiveness at inhibiting pathogens, we isolated the endophytes from both clones (#17 and #33) and cultured them together with Sclerotinia homoeocarpa, the causal agent of 'dollar spot' disease of turfgrasses. After staining with the ROS specific stain nitroblue tetrazolium (NBT), there was a ROS reaction in the form of an orange reaction line between the endophyte from clone #17 and the colonies of S. Homoeocarpa. This orange ROS reaction may be attributed to tetrazolium precipitant resulting from the action of dehydrogenases secreted by S. Homoeocarpa in response to high levels of ROS secreted by endophyte. Tetrazolium salt forms a deep orange colored precipitate when dehydrogenated. Moreover, purple zones that formed around the colonies of the endophyte from clone #17 were also an indication of non-reduced ROS. The purple zones became lightened (ROS shadow) in the proximity of the S. Homoeocarpa colonies, suggesting that the pathogen was responding defensively to ROS secreted by the endophyte. Pronounced inhibitory zones were also evident between the clone #17 endophyte and the colonies of S. homoeocarpa, attesting to the capability of this endophyte to inhibit the pathogen using ROS. In the co-culturing experiments using the endophyte from clone #33 also did not produce zones of inhibition of the pathogen, indicating that it was not effectively inhibiting the pathogen. Our preliminary results in these two studies are consistent with a model for the mechanism of endophyte-enhanced disease resistance in grasses where endophyte-produced ROS plays a prominent role as a defensive agent; with observations in endophyte-modification of plant response to internally-generated ROS and in vitro co-culturing experiments supporting this 'ROS Defensive Model'. If this model is correct, it should be possible to select endophytes with enhanced disease protection capabilities by screening for ROS production in vitro; and employing these endophytes to produce more disease tolerant turf cultivars. Further, ROS production by endophytes may play roles in enhancing drought tolerance (through osmotic adjustment involving proline) and heavy metal tolerance (through the ROS quenching effects of proline). ROS production by endophytes would stimulate plant cells to produce and secrete proline into the plant apoplasts where the proline combines with ROS and any reactive heavy metals, resulting in plants that show enhancements in how they respond to these environmental stresses. Direct effects of endophyte-produced ROS on pathogens may enhance disease resistance in pathogens susceptible to inhibition by ROS. It should also be possible to conduct in vitro experiments to survey turf pathogens that are sensitive to endophyte-produced ROS to identify turf pathogens where endophytes may successfully be employed to enhance turf grass resistance to specific pathogens. Additional studies are planned to evaluate this ROS Defensive Model as the mechanism of disease protection in endophyte-enhanced grasses. We intend to further examine the expression of ROS related genes of endophytes may be responding to the presence of pathogens by enhancing production of ROS. We intend to identify the specific ROS moieties secreted by grass endophytes. Further, using high-ROS and low-ROS endophytes we plan to evaluate the potential for producing turf grass cultivars that show superior environmental stress characteristics due to the effects of proline. We have previously believed that endophyte-produced alkaloids (Alkaloid Defensive Model) were primarily responsible for improved disease resistance in endophyte-enhance turf grasses. The 'ROS Defensive Model' offers an alternate and plausible explanation for improved disease resistance as well as a possible explanation for improved environmental stress tolerance. Future investigations will be targeted at evaluation of both models."
Language:English
References:4
Note:This item is an abstract only!
ASA/CSSA/SSSA Citation (Crop Science-Like - may be incomplete):
Zhang, X., M. Tadych, M. Bergen, and J. F. White. 2008. Are endophyte-produced reactive oxygen species (ROS) responsible for improved fungal disease resistance and environmental stress tolerance in endophyte-enhanced turfgrasses?. Proc. Annu. Rutgers Turfgrass Symp. p. 61-63.
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http://turf.rutgers.edu/research/abstracts/symposium2008.pdf
    Last checked: 11/05/2015
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    Notes: Item is within a single large file
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