Progress 03/15/11 to 03/14/14
Outputs
Target Audience: The target audience thus far for this work has been other scientists working in the field. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Fanhong Meng, BTI Postdoctoral Associate. Designed, analyzed and performed experiments. Prepared a manuscript and presented research at a conference. Zhilong Bao, BTI Postdoctoral Associate. Designed, analyzed and performed experiments. Staci Nugent, Cornell Technician. Designed, performed experiments and analyzed results. How have the results been disseminated to communities of interest? Results have been disseminated to other scientists through publication of findings What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Investigations of the role of pattern-triggered immunity in suppressing Salmonella infection of tomato leaves. A series of experiments were performed to characterize how the tomato immune system responds to attempted infection by Salmonella. We found that Salmonella Typhimurium activates the plant immune system primarily due to its recognition of the flg22 region in Salmonella flagellin. Several previously identified plant genes that play a role in immunity were found to affect the host response to Salmonella. The Salmonella flg22 (Seflg22) peptide induced the immune response in leaves which effectively restricted the growth of Salmonella as well as the plant pathogenic bacterium, Pseudomonas syringae pv. tomato. Induction of plant immune responses by Seflg22 was dependent on the plant FLS2 receptor. Salmonella multiplied poorly in plant tissues similar to other bacteria which are non-pathogenic on plants. However, Salmonella populations increased significantly when co-inoculated with P. syringae pv. tomato but not with type III secretion system mutant of this pathogen. Our results suggest that Salmonella benefits from the immune-suppressing effects of plant pathogenic bacteria, and this growth enhancement may allow Salmonella to reach the necessary infective dose for humans. Requirement of iron for Salmonella survival in tomato fruit. To investigate the genetic means by which Salmonella is able to survive and proliferate within tomatoes, we conducted a screen for bacterial genes of Salmonella enterica serovar Montevideo specifically induced after inoculation into ripe tomato fruit. Among these genes, we found 17 members of the previously described anaerobic Fur (ferric uptake regulator) regulon. Fur is a transcriptional and post-transcriptional regulator known to sense iron, suggesting the importance of this mineral within tomatoes. To test whether iron acquisition is essential for Salmonella growth in tomatoes, we tested a deltafepDGC mutant, which lacks the ability to import iron-associated siderophores. This mutant grew significantly more poorly within tomatoes than did the wild type, but the growth defect of the mutant was fully reversed by the addition of exogenous iron, demonstrating the need for bacterial iron scavenging. Further, dependence upon iron was not apparent for Salmonella growing in filtered tomato juice, implicating the cellular fraction of the fruit as the source of iron required for bacterial proliferation.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Meng F, Altier C, Martin GB. (2013) Salmonella colonization activates the plant immune system and benefits from association with plant pathogenic bacteria. Environ Microbiol. 2013 Feb 27. doi: 10.1111/1462-2920.12113.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2014
Citation:
Nugent SL, Meng F, Martin GB, Altier, C. Acquisition of iron is required for growth of Salmonella in tomato fruit.
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Progress 03/15/12 to 03/14/13
Outputs
Target Audience: The target audience thus far for this work has been other scientists working in the field. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? This work has been performed by two post-doctoral associates and so has been integral to their scientific training. How have the results been disseminated to communities of interest? Results have been disseminated to other scientists through publication of findings. What do you plan to do during the next reporting period to accomplish the goals? Our emphasis during the next reporting period will be to complete the two remaining goals of the project, to: 1) Determine whether differentially expressed genes provide Salmonella with a selective advantage for growth on tomatoes, and; 2) Identify the means by which Salmonella induces genes essential for its colonization of tomatoes. We are currently constructing and testing Salmonella mutants for their ability to survive in tomatoes and will be analyzing the control of the metabolic pathways required for these functions.
Impacts
What was accomplished under these goals?
We have thus far completed the goals of our project to: 1) Identify Salmonella genes that are selectively expressed when the pathogen lives on tomato plants, and; 2) Investigate the role of PAMP-triggered immunity in suppressing Salmonella infection. For goal #1, we used a reporter fusion assay to identify Salmonella genes that are expressed in tomato, but not laboratory medium, thus implicating those likely to be important for survival within this fruit. We found genes in a number of known metabolic assays to be selectively induced (for example, for the acquisition of iron and several carbohydrate sources). This work is currently being extended by making and testing Salmonella mutants of these pathways for their ability to survive and multiply in tomatoes. For #2, we found that the flagellin proteins of Salmonella are the primary source of PAMP-triggered immunity in tomatoes.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Meng F, Altier C, Martin GB. (2013) Salmonella colonization activates the plant immune system and benefits from association with plant pathogenic bacteria. Environ Microbiol. 2013 Feb 27. doi: 10.1111/1462-2920.12113.
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Progress 03/15/11 to 03/14/12
Outputs
OUTPUTS: Information in this report encompasses the dates 03/15/2011 to 03/14/2013 The primary output activity thus far accomplished for this proposal has come in conducting and analyzing the experiments proposed in the work. Additionally, there have been considerable efforts in training and mentoring the two Post-doctoral Associates who are conducting most of the studies. PARTICIPANTS: Craig Altier, PI/PD, has directed the aspects of the project that involve the use of Salmonella. Greg Martin, Co-PI, has directed the aspects of the project that involve pathogen infection of plants. Fanhong Meng, Post-doctoral Associate, has conducted the experiments investigating the plant immune response to infecting bacterial pathogens. Chien-Che Hung, Post-doctoral Associate, has conducted the screening experiments for Salmonella genes important in tomatoes. Staci Nugent, Research Technician, has performed experiments using plants and has participated in screens for important Salmonella genes. This project is being conducted as a partnership between Cornell University and the Boyce Thompson Institute for Plant Research (BTI), a private non-profit research entity. Our collaborator and Co-PI, Greg Martin, serves on the faculty of BTI. TARGET AUDIENCES: The target audience thus far for this work has been other scientists working in the field. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
An important outcome of this work so far has come in better understanding the means by which tomatoes, an important produce plant, can respond to infection by Salmonella, a cause of human disease that can be transfer through produce. We show in published work (Meng et al, 2013) that tomato plants respond to a portion of the Salmonella flagella, creating an immune response in leaves that effectively restricts Salmonella proliferation. Importantly, however, co-infection with the plant pathogen Pseudomonas syringae pv. tomato allows Salmonella to grow. As this plant pathogen is commonly found on tomatoes, co-infection might provide a means for increased plant contamination. A second important outcome has been the development of novel techniques to study the interaction of Salmonella with produce plants. We have created a novel method to rapid screen the Salmonella genome for genes that are either beneficial or detrimental when growing in tomatoes, providing a complete characterization of gene expression at this site and identifying metabolic pathways needed for growth of the pathogen. Further characterization of the results of these assays is ongoing.
Publications
- Meng F, Altier C, Martin GB. (2013) Salmonella colonization activates the plant immune system and benefits from association with plant pathogenic bacteria. Environ Microbiol. 2013 Feb 27. doi: 10.1111/1462-2920.12113.
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