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Published on: March 9, 2021
Mutations in PMR5 result in powdery mildew resistance and altered cell wall composition
John P Vogel1, Theodore K Raab, Chris R Somerville
1USDA Western Regional Research Center, Albany, CA 94710, USA. jvogel@pw.usda.gov
Abstract:
Powdery mildews and other obligate biotrophic pathogens are highly adapted to their hosts and often show limited host ranges. One facet of such host specialization is likely to be penetration of the host cell wall, a major barrier to infection. A mutation in the pmr5 gene rendered Arabidopsis resistant to the powdery mildew species Erysiphe cichoracearum and Erysiphe orontii, but not to the unrelated pathogens Pseudomonas syringae or Peronospora parasitica. PMR5 belongs to a large family of plant-specific genes of unknown function. pmr5-mediated resistance did not require signaling through either the salicylic acid or jasmonic acid/ethylene defense pathways, suggesting resistance in this mutant may be due either to the loss of a susceptibility factor or to the activation of a novel form of defense. Based on Fourier transform infrared analysis, the pmr5 cell walls were enriched in pectin and exhibited a reduced degree of pectin modification relative to wild-type cell walls. In addition, the mutant had smaller cells, suggesting a defect in cell expansion. A double mutant with pmr6 (defective in a glycosylphosphatidylinositol-anchored pectate lyase-like gene) exhibited a strong increase in total uronic acid content and a more severe reduction in size, relative to the single mutants, suggesting that the two genes affect pectin composition, either directly or indirectly, via different mechanisms. These two mutants highlight the importance of the host cell wall in plant-microbe interactions.
Insights
A mutation in the PMR5 gene in Arabidopsis provides resistance to powdery mildew by altering cell wall composition. This finding highlights the crucial role of the plant cell wall in host-pathogen interactions.
Area of Science:
- Plant Pathology
- Molecular Plant-Microbe Interactions
- Plant Cell Biology
Background:
- Obligate biotrophic pathogens exhibit host specialization, potentially involving host cell wall penetration.
- The PMR5 gene is part of a large family of plant-specific genes with unknown functions.
- Plant cell wall structure is a critical interface in plant-microbe interactions.
Purpose of the Study:
- To investigate the role of the PMR5 gene in plant resistance to pathogens.
- To understand the molecular mechanisms underlying PMR5-mediated resistance.
- To explore the impact of PMR5 on plant cell wall composition and structure.
Main Methods:
- Genetic analysis of Arabidopsis mutants (pmr5 and pmr6) for pathogen resistance.
- Fourier transform infrared (FTIR) spectroscopy to analyze cell wall composition.
- Microscopic analysis to assess cell size and expansion defects.
Main Results:
- The pmr5 mutation conferred resistance to powdery mildews (Erysiphe cichoracearum, Erysiphe orontii) but not other pathogens.
- pmr5 cell walls showed increased pectin enrichment and reduced pectin modification.
- pmr5 mutants exhibited smaller cell size, indicating a defect in cell expansion.
- A pmr5/pmr6 double mutant displayed more severe cell wall alterations and size reduction.
Conclusions:
- PMR5 plays a role in susceptibility to powdery mildews, likely by influencing cell wall pectin composition.
- Alterations in cell wall structure, particularly pectin modification, are crucial for plant defense against specific pathogens.
- The study underscores the importance of the host cell wall as a key determinant in plant-microbe interactions.
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