Location: Molecular Plant Pathology Laboratory2015 Annual Report
Objective 1: Identify changes in host gene expression and small RNA-mediated regulation associated with viroid and bacterial infection and disease development as potential targets for disease management. Objective 2: Identify key metabolites that are involved in the early stages of pathogenesis and may have global effects on disease resistance through either their bioactive nature or effect on redox-status. Sub-objective 2.A. Identify and quantify secondary metabolites induced upon infection of tomato with either P. syringae or potato spindle tuber viroid (PSTVd). Sub-objective 2.B. Determine bioactivity of secondary metabolites induced upon infection of tomato with either P. syringae or PSTVd. Sub-objective 2.C. Determine the effect on redox status of secondary metabolites induced upon infection of tomato with either P. syringae or PSTVd. Objective 3: Identify the molecular signals and pathways used by viroids to move through the cytoplasm, enter the nucleus or chloroplast of the host cell, and begin replication. Sub-objective 3.A. Determine the role of host protein 4/1 (and other proteins interacting with 4/1) in the intra- and intercellular movement of PSTVd. Sub-objective 3.B. Use sequence motifs derived from Eggplant latent viroid (ELVd) to redirect mRNAs encoding enzymes involved in terpenoid biosynthesis into the chloroplast.
This project seeks to elucidate specific signaling mechanisms that are involved in plant disease resistance. Plants respond to biotic stress by the integration of responses located in two different cellular compartments, the symplast and the apoplast. Improvement of existing resistance to plant disease requires a more comprehensive understanding of key apoplastic and symplastic responses to pathogen invasion and how they are integrated. In the apoplast, we will examine the complex interplay between secondary metabolites and redox signaling that controls early events in bacterial and viroid pathogenesis as well as other responses triggered by long distance signaling. In the symplast, we will examine the molecular interactions between viroids and their hosts to determine how these small RNA molecules replicate and move between organelles within a single cell or over long distances between cells. The long-term objective of this multidisciplinary project is to understand the role of plant-pathogen signaling in disease resistance in sufficient detail that novel strategies can be developed to render plants resistant/immune to pathogen infection. In the intermediate term, we will test the ability of certain viroid-derived targeting signals to redirect mRNAs to the chloroplast, thereby adding novel biosynthetic capabilities to chloroplast metabolism with the need for chloroplast genome transformation.
We have been examining the early events that take place in the plant apoplast when a bacterial pathogen first comes in physical contact with the plant cell. We have continued to support our finding that certain pathogens induce the plant to produce redox-active secondary metabolites and that many of these same metabolites have a bioactive affect on the host/pathogen interaction. Recent methods that we developed to examine apoplast metabolites indicate that pathogenic interactions may weaken the apoplast/symplast barrier, allowing controlled flow/leakage of symplastic and vacuolar metabolites into the apoplast. We are testing this hypothesis from different approaches including microscopic, chemical, electrochemical and biological. This may help demonstrate that one role of apoplast redox potential is its effect on the plasmalemma membrane potential, which could allow leakage. This could lead to new strategies for controlling disease by aerial application of metabolites that would buffer the apoplast redox potential at beneficial levels.
1. New method for monitoring bacterial inoculation of plants. Bacterial plant diseases cause major damage to crops each year and the cost of controlling them adds greatly to production costs and often involves antibiotics which are a public concern. The plant leaf apoplast, which is the cell wall region just outside the plant cell itself, is the first line of defense against most aerial pathogens. Scientists in Beltsville, Maryland, developed a method that monitors changes in apoplastic phenolics following bacterial inoculation. Using this method we demonstrated that the accumulation of apoplastic phenolics is stimulated 'in planta' in response to bacterial inoculation. In addition the procedure unexpectedly indicated that changes in the physical integrity of the apoplast/cytoplasmic barrier occur during this interaction, causing leakage from the cell. The leaf apoplast is highly vulnerable to manipulation either by genetic engineering or direct application of materials to leaves or roots. This information will benefit plant scientists and breeders who are devising new strategies to improve disease resistance while decreasing the use of chemical pesticides and antibiotics.
Averyanov, A.A., Lapikova, V.P., Pasechnik, T.D., Abramova, O.S., Gaivoronskaya, L.M., Kuznetsov, V., Baker, C.J. 2014. Preillumination of rice blast conidia induces tolerance to subsequent oxidative stress. Fungal Biology. 118:743-753.
Baker, C.J., Mock, N.M., Averyanov, A.A. 2015. Induction of a viable but not culturable (VBNC) state in some Pseudomonas syringae pathovars upon exposure to oxidation of an apoplastic phenolic, acetosyringone. Physiological and Molecular Plant Pathology. 89:16-2.