A role for beta-sitosterol to stigmasterol conversion in plant-pathogen interactions.
Thomas Griebel1, Jürgen Zeier2
1Julius-von-Sachs-Institute of Biological Sciences, University of Würzburg, Julius-von-Sachs Platz 3, D-97082 Würzburg, Germany.
Summary
Plant infection by microbes increases stigmasterol, a sterol that enhances pathogen growth. Blocking stigmasterol production boosts plant resistance, revealing a new susceptibility mechanism in Arabidopsis thaliana.
Area of Science:
- Plant Pathology
- Molecular Biology
- Biochemistry
Background:
- Plants exhibit metabolic changes upon microbial infection, influencing resistance or susceptibility.
- Lipid composition analysis reveals significant metabolic shifts during plant-pathogen interactions.
Purpose of the Study:
- To investigate the role of phytosterol accumulation, specifically stigmasterol, in plant responses to bacterial leaf infection.
- To elucidate the metabolic pathway and regulatory mechanisms of induced stigmasterol synthesis.
- To determine the impact of stigmasterol on plant defense signaling and susceptibility to Pseudomonas syringae.
Main Methods:
- Analysis of leaf lipid composition in Arabidopsis thaliana during Pseudomonas syringae infection.
- Genetic analysis using cyp710A1 mutant lines impaired in stigmasterol synthesis.
- Exogenous application of stigmasterol to assess its effect on plant resistance.
- Investigation of signaling pathways (salicylic acid, jasmonic acid, ethylene) involved in stigmasterol induction.
- Biochemical analysis of microsomal and plasma membrane preparations.
Main Results:
- Bacterial infection induces stigmasterol accumulation via cytochrome P450 CYP710A1-mediated C22 desaturation of beta-sitosterol.
- Arabidopsis cyp710A1 mutants show enhanced resistance to P. syringae, while exogenous stigmasterol reduces resistance.
- Stigmasterol accumulation is triggered by pathogen-associated molecular patterns and reactive oxygen species, independent of major defense hormone pathways.
- Induced stigmasterol is incorporated into plant membranes and attenuates the expression of the defense regulator flavin-dependent monooxygenase 1.
Conclusions:
- Induced sterol C22 desaturation and subsequent stigmasterol accumulation favor pathogen multiplication and increase plant susceptibility.
- Pseudomonas syringae promotes disease susceptibility by stimulating sterol C22 desaturation, altering membrane composition.
- This study identifies a novel mechanism of pathogen-induced susceptibility mediated by phytosterol metabolism.
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