Physiological and molecular analysis of dnd "defense, no death" mutants of Arabidopsis.

다국어 초록 (Multilingual Abstract)

Plant diseases cause billions of dollars in damage to crops annually, making dissection of the molecular mechanisms of plant disease resistance an economically important task. Gene-for-gene resistance mediated by plant <italic> R</italic> genes and pathogen <italic>avr</italic> genes has long been associated with the hypersensitive response (HR). Previously, <italic>Arabidopsis thaliana </italic> “defense, no death” (<italic>dnd</italic>) mutants were identified based on their failure to produce the HR when inoculated with <italic> P. syringae</italic> carrying the avirulence gene <italic>avrRpt2</italic>. The first objective of this study was to characterize the <italic>dnd2</italic> mutants in relation to defense. Like the previously characterized <italic> dnd1</italic> mutant plants, <italic>dnd2</italic> mutants responded to avirulent pathogens by activating <italic>avr</italic>-dependent defenses despite the absence of the HR. In addition, <italic>dnd2</italic> plants exhibited a constitutive systemic resistance associated with elevated levels of salicylic acid (SA). SA was found to be required for the systemic resistance of <italic>dnd2</italic> plants, but was not necessary for the HR<super>−</super> phenotype displayed by the mutant plants. SA-independent pathways not normally activated by <italic> P. syringae</italic> infection were activated in <italic>dnd</italic> plants, as indicated by the marker for SA-independent signaling, PDF 1.2. A map-based cloning project was initiated which identified a precise genetic interval spanning <italic>DND2</italic>. Focused shotgun complementation experiments were initiated using subclones from within this region. The roles of reactive oxygen species (ROS) and the enzymes that scavenge these signaling molecules were examined in relation to the HR<super>−</super> phenotype of <italic> dnd</italic> plants. Northern analysis of ROS scavenger mRNA revealed no significant differences in gene expression between wild type and <italic>dnd</italic> plants, suggesting that ROS scavengers are not blocking ROS signaling for the HR. Finally, the dwarfed stature of <italic>dnd</italic> plants was could be partially corrected by altered growth conditions, specifically the soil mix. Chemical analysis of soil mixes after 6 weeks of use suggested that cations and pH might be involved in the growth phenotype. The effect of K<super>+ </super>, Ca<super>2+</super>, Na<super>+</super>, and pH on <italic>dnd</italic> plant growth was then tested in agar-based media. The <italic>dnd</italic> plants did not respond to increasing concentrations of Ca<super>2+</super> in parallel with wild-type plants. K<super>+</super>, Na<super>+</super> and pH impacted <italic>dnd1, dnd2</italic>, and wild-type plants similarly.