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The mlo resistance alleles to powdery mildew infection in barley trigger a developmentally controlled defence mimic
M Wolter1, K Hollricher, F Salamini
1Biologie I, RWTH Aachen, Germany.
Abstract:
Recessive mlo resistance alleles of the Mlo locus in barley control a non race-specific resistance response to infection by the obligate biotrophic fungus Erysiphe graminis f.sp. hordei. All the mlo alleles analysed stop fungal growth at the same developmental stage within a subcellularly restricted, highly localized cell wall apposition directly beneath the site of abortive fungal penetration. We report that near-isogenic lines carrying the alleles mlo1, mlo3 or mlo5 undergo dramatic spontaneous formation of cell wall appositions, not only in the absence of the fungal pathogen but also in sterile grown plants. A comparative study of spontaneous and infection-triggered cell wall appositions reveals a high degree of similarity with respect to structure, chemical composition and distinct localization within plant tissue. We show that the rate of spontaneous apposition formation is dependent on the genetic background of the plant and that its onset is under developmental control. Furthermore, spontaneous formation of wall appositions is specifically triggered by mlo alleles, since it is unaffected in the presence of the race-specific resistance allele Mlg. We propose a model for the function of the Mlo locus that suggests that both Mlo and mlo alleles control qualitatively the same apposition-based resistance mechanism, which, in the presence of the wild-type Mlo allele, is merely less efficient to provide protection against the currently common races of E. graminis f.sp. hordei.
Insights
Recessive mlo alleles in barley trigger spontaneous cell wall appositions, a key plant defense mechanism. This finding reveals a novel aspect of Mlo locus function in plant immunity against powdery mildew.
Area of Science:
- Plant pathology
- Molecular genetics
- Plant-microbe interactions
Background:
- The Mlo locus in barley controls non-race-specific resistance to powdery mildew (Erysiphe graminis f.sp. hordei).
- mlo resistance alleles halt fungal growth via cell wall appositions beneath penetration sites.
Purpose of the Study:
- To investigate spontaneous cell wall apposition formation in barley lines with mlo resistance alleles.
- To compare spontaneous and infection-triggered appositions and understand Mlo locus function.
Main Methods:
- Utilized near-isogenic barley lines carrying mlo1, mlo3, or mlo5 alleles.
- Conducted comparative studies of spontaneous and infection-induced cell wall appositions.
- Analyzed the genetic background and developmental control of apposition formation.
Main Results:
- Near-isogenic lines with mlo1, mlo3, or mlo5 alleles exhibited spontaneous cell wall appositions.
- Spontaneous and infection-triggered appositions showed structural and compositional similarities.
- Apposition formation rate depended on genetic background and developmental stage.
- Spontaneous formation was specifically linked to mlo alleles and unaffected by Mlg.
Conclusions:
- The Mlo locus, through both Mlo and mlo alleles, regulates an apposition-based resistance mechanism.
- Wild-type Mlo alleles confer less efficient resistance against common powdery mildew races.
- Spontaneous appositions offer insights into basal plant defense activation and Mlo function.