The objectives of this project are to understand the role of the plant hormone auxin during pathogen infection and disease development and to elucidate the mechanisms by which the plant bacterial pathogen Pseudomonas syringae modulates auxin synthesis and signaling in plants. The investigators will use a combination of genetic, molecular and biochemical approaches to identify the biosynthetic pathways used by P. syringae to synthesize auxin and to investigate how P. syringae virulence factors alter host auxin physiology to promote pathogenesis. The proposed experiments are innovative and relevant because they integrate studies of the pathogen, plant host and auxin synthesis and signaling within the host and should yield improved understanding of the role(s) of auxin (and potentially other plant hormones) and hormone signaling during pathogen infection and disease development. The work will benefit society at large through a better understanding of pathogen virulence and disease susceptibility, and may lead to novel control methods and development of plants with increased disease resistance. The project will provide stimulating and valuable research and educational opportunities for high school, undergraduate, graduate and postdoctoral students in the investigators' laboratories, and both laboratories work with educational programs to attract students from under-represented groups to become involved in the research.
This is a collaborative project between Dr. Barbara Kunkel's laboratory at Washington University and the PI’s laboratory at Texas A&M University with a total funding support of $299,581.00 to the PI’s laboratory for three years. The proposal consists of three objectives: Objective I: Investigate whether P. syringae strain DC3000 produces auxin as a virulence factor. Objective II: Investigate the mode of action of the P. syringae virulence factor AvrRpt2 in modulating host auxin physiology. Objective III. Investigate the roles of auxin during P. syringae strain DC3000 pathogenesis. The PI’s laboratory mainly focused on Objective II and Dr. Kunkel's laboratory focused on Objective I and III. Thus here the report mainly focuses on Objective II. Plant physiological and cellular processes are deliberately orchestrated by the collective action of plant growth hormones. In addition to the roles in growth and development, the homeostasis of individual hormones and their crosstalk affect the outcomes of plant-pathogen interactions. Modulation of plant auxin physiology and signaling is emerging as a common virulence strategy for phytobacteria to cause diseases. However, the underlying mechanisms remain largely elusive. With this funding support, the PI’s laboratory has found that Pseudomonas syringae type III effector AvrRpt2 alters Arabidopsis auxin physiology and promotes auxin sensitivity via stimulating the turnover of Aux/IAA proteins, the key negative regulators in auxin signaling. Thus, the study reveals a novel mechanism of pathogen virulence, and will have broad implication for the understanding of crosstalk between hormone signaling and plant defense. The results on the pathogen virulence mechanisms from the PI’s laboratory have been reported timingly to the research community with three publications in peer-reviewed journals (Mol. Plant Microbe Interact.2011; Plant Physiology 2013; Plant Journal 2013). One of the key contributions achieved during this project development is to train and advance human resource development in the scientific field. As one of the PI’s first Federal funding supports, this project development enabled the PI, as a junior faculty to successfully recruit undergraduate students, graduate students, postdoctoral fellow and visiting scientists into the laboratory. The funding support was fundamentally essential to establish the lab and set up the research, teaching and education programs. Along with the development of this project, the PI has expanded the research programs with various angles yet centering on molecular plant-microbe interactions. The PI has secured additional funding supports for other research programs, published research results timingly, and given talks in national and international conferences. The PI has been promoted to Associate Professor with tenure by Texas A&M University in 2013. In addition, the postdoctoral fellow, Dr. Shujing Wu and graduate student, Mr. Fuhao Cui, who initiated and led this project, have successfully mastered various molecular techniques and developed the capacity to design the experiment, interpret the results, formulate new hypothesis and teach students. Dr. Wu has established his own lab recently and Mr. Cui is defending his PhD thesis in December 2013. During this NSF funding period, the lab hosted several undergraduate students from Texas Rio Grande Valley and the United States-Mexico border region for research experience supported by NSF REU program. These undergraduate students have actively participated in this project through characterization of transgenic plants and phenotypic assays. These activities increased the curiosity of these students to science and leveraged the enrollment of underrepresented students from the most economically disadvantaged areas of the country into life science programs.
