Necrotrophic plant pathogens are diverse bacterial and fungal species that survive by extracting nutrients from killed plant cells. Due to this mode of nutrition they cause host cell death (necrosis) by releasing toxins into host tissues. Failure to limit necrosis by the plant leads to enhanced infections resulting in plant diseases that culminate in death and decay of the entire infected plant or its parts causing significant losses in crop yield. The biological processes underlying host responses to necrotrophic infections and the associated necrosis are not understood. The overall goal of this project is to determine the molecular mechanisms of plant responses to necrotrophic pathogens. Plant proteins that limit necrotrophic infections that have been identified will be used to determine the biological basis of host resistance or susceptibility to pathogen and stress induced necrosis. BOS1 (Botrytis Susceptible 1) is an R2R3MYB transcription factor that limits pathogen and stress induced necrosis. The functions of novel components of BOS1 mediated resistance including the role of BOS1 interacting E3 ligases will be studied and their regulatory role in resistance to necrosis and/or cell death caused by pathogens and pathogen derived toxins determined. The nature of cell death caused by necrotrophic pathogens and mechanisms of plant responses will be established using molecular, genetic and biochemical approaches. Genome scale changes in gene expression associated with pathogen induced necrosis and the role of BOS1 interacting proteins will be deciphered. This project will generate new knowledge on biochemical, molecular and genetic mechanisms of plant disease resistance and elucidate some of the fundamental differences in host responses to biotrophic and necrotrophic pathogens. In addition, the project will train undergraduate students from diverse institutions to promote student interest in plant biology. The project will promote graduate student training and education and research and mentoring skills for postdoctoral scientists in various aspects of plant biology.
Federal Award ID: 0749865 Plant pathogens are major problems in crop production. Current plant disease control strategiesare dominated by application of chemical fungicides which is not desirable dueto environmental and public safety with chemical residues. Research that aimsto understand fundamental processes that affect how plants fend off infectionmay facilitate the development of genetic resistance. Resistance that relies onenhancing the plants innate ability to fight infection is more sustainable and environmentallyfriendly. The current project focused on necrotrophic fungal pathogens, major disease causal agents in a variety of crops. This class of pathogens causes cell death (necrosis) to initiate infection and further grow and expand to cause more aggressive diseases. The goal of the current project is to determine the molecular and biochemical basis cell death (necrosis) caused by endogenous and environmental signals including infection by pathogens. The activities were aimed at understanding the biological processes that contribute to immune responses to necrotrophic fungi through their role in regulating cell death. This project identified key regulators of cell death/necrosis in the model plant Arabidopsis. The Botrytis Susceptible 1 Interactor (BOI) and related genes encode RING E3 ligases that contribute to plant defense through their suppressive role on necrosis and hypersensitive cell death. BOI physically interacts and ubiquitinates Arabidopsis BOS1, an R2R3MYB transcription factor previously implicated in resistance to pathogens. Plants with reduced BOI transcript levels were more susceptible to the necrotrophic fungus Botrytis cinerea. In addition, BOI RNAi plants exhibited increased cell death induced by the phytotoxin α-picolinic acid, and by a virulent strain of the bacterial pathogen, Pseudomonas syringae, coincident with peak disease symptoms. BOI expression was enhanced by B. cinerea, salicylic acid, 1-aminocyclopropane-1-carboxylic acid and salt stress but repressed by the plant hormone gibberellin (GA), indicating a complex regulation of BOI gene expression. BOI RNAi plants exhibit reduced growth responsiveness to GA. In addition, three Arabidopsis BOI RELATED GENES (BRGs) contribute to B. cinerea resistance and suppression of disease-associated cell death through mechanisms overlapping and distinct with BOI. BOI and BRGs represent a subclass of RING E3 ligases that contribute to plant disease resistance and abiotic stress tolerance through the suppression of pathogen infection as well as stress-induced cell death. The findings from the studies in this project contributed to the understanding of the molecular and biochemical mechanisms of cell death that occurs during responses to biotic and abiotic stresses. These and other findings of the project are described in peer reviewed journal. With regards to human resources development, this project partially or fully contributed to the training of two graduate students and two post-doctoral fellows. The funding was used to pay their salaries and/or support research expenses. The post-doctoral fellows were mentored in laboratory, grant and manuscript writing skills. We have also trained undergraduate students from various universities in the US in research skills in molecular and genetics of plants. The goal of such internships was to encourage students, through this research experience, to purse graduate educations in science. Indeed, some of the summer interns went on to join graduate schools at various institutions. Further, the research approaches and outcomes are being used in class room teachings and training of students in the lab. The class teachings involving molecular research approaches benefit students through demonstrating research approaches as well as enhancing their knowledge with experimental results. Recent progress and advances in the specific areas are also brought to the classroom. Overall, both the research and training objectives were accomplished.
