Molecular Characterization of Genetic Components of Pathogen Defense in Arabidopsis

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Ramesh Raina


Arabidopsis, Histone demethylation, Plant defense, Pseudomonas syringae, Reactive oxygen species, Salicylic acid

Subject Categories

Molecular Biology


Plant defense against pathogens involve complex interplay of several defense-associated factors. This work characterizes three Arabidopsis thaliana genes that play critical roles in regulating defense responses against the bacterial pathogen, Pseudomonas syringae. We have previously described phenotypic characterization of the hrl1 mutant of Arabidopsis; a lesion-mimic mutant that is small in size compared to the wild type, spontaneously develops necrotic lesions mimicking the hypersensitive response, constitutively expresses several defense-related genes and has enhanced resistance against a variety of pathogens. In this work I cloned the HRL1 gene by a map-based cloning approach. HRL1 codes for a 4-hydroxybenzoate polyprenyl diphosphate transferase, which catalyzes a rate limiting step in ubiquinone biosynthesis. My studies suggest that mitochondrial metabolic reactive oxygen species are key regulators of Arabidopsis basal resistance against P. syringae. I further identified and characterized a suppressor of the hrl1 mutant; JMJ27 (ARABIDOPSIS JUMONJI 27) gene of Arabidopsis. JMJ27 codes for a JmjC domain-containing H3K9 histone demethylase and is required for defense against P. syringae. Additionally, another novel component of plant defense, SMALL DEFENSE-ASSOCIATED PROTEIN 1 (SDA1) gene of Arabidopsis, was characterized. SDA1 was identified as a gene that is constitutively expressed to high levels in the hrl1 mutant. SDA1 defines a novel class of small pathogen defense proteins required for defense against P. syringae.

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