Investigating the Role of BLADE-ON-PETIOLE Genes and Hydrophobic Cell-Wall Polymer Suberin in Arabidopsis thaliana Defense Against Bacterial and Fungal Pathogens

ABSTRACT In this thesis, I use the model plant species, Arabidopsis thaliana (Arabidopsis), to examine disease resistance associated with BLADE-ON-PETIOLE (BOP) 1 and 2 genes and suberin polymer. Plants are the target of a broad spectrum of pathogens, including fungi and bacteria. To detect and actively fight these pathogens, plants have innate and induced immune systems as well as pre-formed barriers. Firstly, I examined the role of the BOP1/2 genes of Arabidopsis in plant defense against bacterial and fungal pathogens. BOP1/2 genes are known to control plant development and belong to an evolutionarily conserved subclade of BTB-ankyrin transcription co-factors in plants. A paralog of BOP1/2, NPR1 is a positive regulator of the plant defense response known as systemic acquired resistance (SAR). Using a direct pathogen test approach to examine the resistance and susceptibility of BOP1/2 mutants to Pseudomonas syringae and Botrytis cinerea, I found that BOP1/2 have a role in defense against pathogens, and specifically in innate immunity. Secondly, I examined the role of the hydrophobic cell-wall polymer suberin in protecting Arabidopsis against pathogenic bacteria and fungi. Suberin forms a complex extracellular hydrophobic lipid-based barrier that is deposited in various tissues in terrestrial plants. Suberin serves as a protective barrier against abiotic and biotic environmental stresses and plays important roles in controlling water and ion movement. Mutants of Arabidopsis defective in root suberin, as well as mutants ectopically overexpressing suberin were tested in relation to resistance or susceptibility to both fungal and bacterial pathogens. Root suberin mutants differed from wild type control plants in susceptibility to the fungal pathogen Fusarium avenaceum. Strikingly, I also found that the presence of suberin in the leaves of Arabidopsis promotes Botrytis cinerea infection spread as well as water loss in the leaves of the plants.