Innate immunity in Arabidopsis : molecular mechanisms of HOPA1 and AVRRS4 - specific disease resistance signaling pathways

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Title from PDF of title page (University of Missouri--Columbia, viewed on January 26, 2011).Thesis advisor: Dr. Walter Gassmann,Vita.Ph. D. University of Missouri--Columbia 2009.Plants have evolved several layers of predetermined defenses, collectively called the innate immune system. Because of its effectiveness effector-triggered immunity (ETI) is a highly valuable agronomic trait. However, ETI has the potential to be highly deleterious to the host and needs to be tightly controlled. To understand the molecular basis for ETI, I used genetic approaches. Using a loss of resistance screen, I cloned the hopA1-specific RPS6 (Resistance to Pseudomonas syringae 6) resistance gene. Using a gain of resistance screen, we cloned SRFR1 (Suppressor of RPS4-RLD), which reactivates avrRps4- and hopA1-triggered immunity. Based on the genetic, molecular, biochemical, and phylogenic evidence, we propose that SRFR1 functions in a transcriptional repressor complex that balances plant immunity and development. To date RPS4 and RPS6 are the only Arabidopsis TIR-NBS-LRR resistance genes for which P. syringae effectors are known. Both pathways are negatively regulated by SRFR1. Functional characterization of RPS6 and SRFR1 will provide an important piece of the ETI puzzle.Includes bibliographical reference

Identifying the interaction between AtSRFR1 with AtTPL and AtTLR3 in planta

Abstract only availablePlant disease caused by pathogens results in large economic losses in crop yield annually. Our previous study found a negative regulator of effector triggered immunity in Arabidopsis thaliana. Mutations in SRFR1 (Suppressor of rps4-RLD) enhance resistance to the pathogenic bacterium Pseudomonas syringae pv. tomato strain DC3000 expressing avrRps4. We hypothesize that SRFR1 functions similar to Ssn6, a possible ortholog of SRFR1. Ssn6 - Tup1 is a well- known conserved system of transcriptional repression in eukaryotes. We are investigating whether SRFR1 interacts with Tup1-orthologs of Arabidopsis. We chose TOPLESS (TPL), which functions as a transcriptional repressor regulating shoot development, and TOPLESS RELATED (TLR). We first amplified cDNAs of TPL and TLR from Arabidopsis and cloned them into the entry vector of the Gateway compatible system. We then subcloned TPL and TLR into various vectors using Gateway system. These vectors introduced sequences of various tags such as Myc or HA at the 5' end. Using Agrobacterium -mediated transient expression in Nicotiana benthamiana, we will test for interactions between SRFR1 with TPL and TLR. Protein samples will be extracted for co-immunoprecipitation assay to reveal the presence or absence of interactions between these proteins. We will perform western blots to look for these interactions. Cloning TPL and TLR transcripts into plasmid vectors for Agrobacterium transformation required the majority of time and effort for this project. If the two proteins interact, it will be evidence of the importance for SRFR1 in transcriptional repression.Gyeongsang National Universit

Searching for the RPS6 resistance gene in Arabidopsis [abstract]

Abstract only availableFaculty Mentor: Dr. Walter Gassmann, Plant SciencesPlants have several methods of protecting themselves against disease, the most effective of which is the gene-for-gene reaction.  In order for a plant to show resistance using the gene-for-gene reaction, an effector protein from the bacteria and a disease resistance protein in the plant must both be present.  When a plant containing a disease resistance protein is exposed to a pathogen, the protein specifically recognizes the effector protein from the bacteria, and a series of resistance responses is triggered in the plant.  Working with Arabidopsis, we are currently trying to isolate the RPS6 resistance gene that specifies resistance to the hopPsyA gene from the bacterial pathogen Pseudomonas syringae pv. syringae. Possible RPS6 resistance genes have been narrowed down to seven candidate genes in the bottom of chromosome 5.  Transformation of an RPS6 mutant with wild-type DNA encoding one of the seven candidate genes indicated complementation, but this result is very preliminary.  Inoculation of T-DNA knock-outs in this gene will verify whether or not we have successfully found RPS6.  If the plants are susceptible when infiltrated with Pseudomonas syringae with hopPsyA, we will know that we have located the RPS6 resistance gene.  Our work contributes to the knowledge of plant immunity.  Better understanding of the gene-for-gene reaction and its relation to disease resistance, along with further tests, will lead to the possibility of engineering plants.  The engineering of plants with improved innate immunity will in turn reduce the need to use expensive and ecologically damaging pesticides

Molecular mechanisms of effector-triggered immunity in plants [abstract]

Only abstract of poster available.Track V: BiomassLike other organisms, plants are continuously exposed to potential pathogens. Yet most plants are resistant to most pathogens because of multi-layered defenses. The most potent forms of plant defenses are triggered when the plant perceives pathogen-derived molecules. This innate immune system is a very valuable trait: when harnessed for agriculture, the innate ability of plants to resist pathogens lessens the need for energetically and environmentally costly pesticides. However, these strong inducible defenses also have the potential to adversely affect the plant if not properly kept in check. Plants with constitutively activated defenses display a severe reduction in biomass and viability. Using complementary biochemical, cell biological and genetic approaches, my lab is studying the machinery that positively or negatively controls the activation of pathogen defenses in the reference plant Arabidopsis thaliana. A proper balance between plant immune system activation and suppression will maximize biomass production. Principles worked out with Arabidopsis are very relevant for crop plants. The Arabidopsis genes we are studying are conserved throughout the plant kingdom. Currently we are applying our knowledge of the plant immune system gained with Arabidopsis to grapevine. We study the difference in fungal disease susceptibility between Cabernet sauvignon and Norton, a North American grapevine species and the State Grape of Missouri, and find genes that are well known from Arabidopsis work to respond differently in the two species

Pathogen susceptibility to Pseudomonas syringae in Arabidopsis thaliana [abstract]

Abstract only availablePeptides may act as regulatory molecules that coordinate cellular responses needed for growth, differentiation and development. A novel family of small peptides, encoded by the DEVIL (DVL) gene family, was identified in a screen for genes that alter plant development. During further investigation of these genes a double mutant was made, DVL DISTORTED, that showed an apparent increase in disease susceptibility. The objective of this study was to determine the pathogen susceptibility of these plants. The study tested the mutants' susceptibility to Pseudomonas syringae, a bacterial pathogen of plants. Pseudomonas syringae pv. tomato strain DC3000 and DC3000 expressing the avirulence gene avrRps4 were injected into the plants of interest and compared to wildtype. A growth curve assay was also conducted which measured the number of bacterial colonies able to grown in each leaf inoculated with DC3000, DC3000 (AvrRps4), or DC3000 (HopPsyA). Initial results indicated that DVL mutant plants are more susceptible to Pseudomonas syringae. Trials are being repeated to confirm results.Life Sciences Undergraduate Research Opportunity Progra