Dissecting Transcriptional Regulation of Rpp8 in Arabidopsis thaliana
Abstract
Plants have evolved physical barriers and inducible defense responses to combat
microbial pathogens. Inducible responses are mediated by R proteins, which recognize
invading pathogens. R proteins must be precisely regulated to provide effective
resistance, without inhibiting normal plant growth. However, little is known about R
gene regulation under defense-inducing conditions. The interaction between the
oomycete Hyaloperonospora parasitica and the model plant Arabidopsis thaliana
provides an excellent model system to explore R gene regulation. My research focuses
on RPP8, a CC-NBS-LRR gene, which provides resistance to the H. parasitica isolate
Emco5. Previous work in the McDowell lab suggested that RPP8 is upregulated during
defense responses. My research shows that RPP8 alleles from the Columbia and
Landsberg erecta ecotypes are upregulated by H. parasitica and the defense signaling
molecule salicylic acid, suggesting a potential feedback loop. RPP8-Ler is also
systemically upregulated after infection of the bacterial pathogen Pseudomonas syringae
pv. tomato DC3000. Additionally, RPP8-Ler expression is increased during wounding
and heat stress. I also examined the role of regulatory cis elements in the RPP8
promoter. Three W-boxes are essential for basal and inducible RPP8 expression, and are
required for resistance to Emco5. The X-box, a unique cis element in the RPP8
promoter, is essential for strong basal expression and wound-induced upregulation, and
affects spatial expression of RPP8-Ler. However, the X-box is not required for RPP8-Ler upregulation during pathogen or SA treatment. R genes may be induced as part of
global defense responses, which could prime the host for more effective pathogen
recognition.
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