Epsilon Archive for Student Projects

Abstract

Plants constantly monitor cell wall status and their surrounding environments to ensure survival and optimal growth. It is crucial for plants to detect internal physiological changes and external stimuli, subsequently responding to these cues through a diverse repertoire of receptor-like kinases localized in the plasma membrane. The boundary between cell wall integrity (CWI) and pattern-triggered immunity (PTI) overlaps, as microbial pathogens have to penetrate the cell wall to infect host plants. Consequently, cell wall damage caused by pathogens is often unavoidable and can be perceived by both cell wall integrity maintenance mechanisms and the plant’s immune layers. While it is known that PTI modulates CWI signaling, the reverse relationship remains unexplored.

This thesis demonstrates that the cell wall integrity sensor THESEUS1 (THE1) modulates PTI responses as a negative regulator, showing the interconnection between CWI maintenance and immunity. I show that impaired THE1 triggers an autoimmune response, suggesting a role for THE1 in suppressing inappropriate immune activation in the absence of cell wall damage (CWD); this is supported by the hypersensitive response of the the1-1 mutant and its elevated basal expression of the immune marker gene FLG22-INDUCED RECEPTOR-LIKE KINASE1 (FRK1). Furthermore, I show that THE1 mediates a synergistic hyperinduction of FRK1 expression upon CWD and immune elicitor, revealing how CWI signaling interplays with defense signaling. Moreover, this thesis highlights that THE1 is essential for photosystem II recovery during cell wall damage following immune activation. Additionally, this study shows that THE1 and the CWI downstream Zinc finger of Arabidopsis thaliana (ZAT) transcription factors regulate the growth-defense trade-off, with both contributing to a growth reduction as evidenced by growth inhibition assays.

Ultimately, this study explores the molecular and physiological interplay between CWI and PTI, demonstrating that THE1-mediated CWI signaling negatively regulates PTI, while THE1-independent ZAT transcription factors play a role in the growth-defense trade-off. These findings provide insights into how plants balance the trade-off between growth and defense to adapt to environmental challenges.