title: Elevated early callose deposition results in complete penetration resistance to powdery mildew in Arabidopsis.
abstract: A common response by plants to fungal attack is deposition of callose, a (1,3)-β-glucan polymer, in the form of cell wall thickenings called papillae, at site of wall penetration. While it has been generally believed that the papillae provide a structural barrier to slow fungal penetration, this idea has been challenged in recent studies of Arabidopsis (Arabidopsis thaliana), where fungal resistance was found to be independent of callose deposition. To the contrary, we show that callose can strongly support penetration resistance when deposited in elevated amounts at early time points of infection. We generated transgenic Arabidopsis lines that express POWDERY MILDEW RESISTANT4 (PMR4), which encodes a stress-induced callose synthase, under the control of the constitutive 35S promoter. In these lines, we detected callose synthase activity that was four times higher than that in wild-type plants 6 h post inoculation with the virulent powdery mildew Golovinomyces cichoracearum. The callose synthase activity was correlated with enlarged callose deposits and the focal accumulation of green fluorescent protein-tagged PMR4 at sites of attempted fungal penetration. We observed similar results from infection studies with the nonadapted powdery mildew Blumeria graminis f. sp. hordei. Haustoria formation was prevented in resistant transgenic lines during both types of powdery mildew infection, and neither the salicylic acid-dependent nor jasmonate-dependent pathways were induced. We present a schematic model that highlights the differences in callose deposition between the resistant transgenic lines and the susceptible wild-type plants during compatible and incompatible interactions between Arabidopsis and powdery mildew.
authors: Phytopathology and Biochemistry, Biocenter Klein Flottbek, University of Hamburg, 22609 Hamburg, Germany.
authors: Dorothea
authors: D
authors: Ellinger
authors: Marcel
authors: M
authors: Naumann
authors: Christian
authors: C
authors: Falter
authors: Claudia
authors: C
authors: Zwikowics
authors: Torsten
authors: T
authors: Jamrow
authors: Chithra
authors: C
authors: Manisseri
authors: Shauna C
authors: SC
authors: Somerville
authors: Christian A
authors: CA
authors: Voigt
mesh_terms: D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000235:genetics / Q000276:immunology* / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001203:Ascomycota / Q000502:physiology*; D003517:Cyclopentanes / Q000378:metabolism; D060467:Disease Resistance / Q000276:immunology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D005936:Glucans / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008954:Models, Biological; D054883:Oxylipins / Q000378:metabolism; D010641:Phenotype; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology*; D030821:Plants, Genetically Modified; D020156:Salicylic Acid / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D005936:Glucans; D054883:Oxylipins; D049452:Green Fluorescent Proteins; C011006:jasmonic acid; C048306:callose; D020156:Salicylic Acid