title: Plant defense mechanisms are activated during biotrophic and necrotrophic development of Colletotricum graminicola in maize.
abstract: Hemibiotrophic plant pathogens first establish a biotrophic interaction with the host plant and later switch to a destructive necrotrophic lifestyle. Studies of biotrophic pathogens have shown that they actively suppress plant defenses after an initial microbe-associated molecular pattern-triggered activation. In contrast, studies of the hemibiotrophs suggest that they do not suppress plant defenses during the biotrophic phase, indicating that while there are similarities between the biotrophic phase of hemibiotrophs and biotrophic pathogens, the two lifestyles are not analogous. We performed transcriptomic, histological, and biochemical studies of the early events during the infection of maize (Zea mays) with Colletotrichum graminicola, a model pathosystem for the study of hemibiotrophy. Time-course experiments revealed that mRNAs of several defense-related genes, reactive oxygen species, and antimicrobial compounds all begin to accumulate early in the infection process and continue to accumulate during the biotrophic stage. We also discovered the production of maize-derived vesicular bodies containing hydrogen peroxide targeting the fungal hyphae. We describe the fungal respiratory burst during host infection, paralleled by superoxide ion production in specific fungal cells during the transition from biotrophy to a necrotrophic lifestyle. We also identified several novel putative fungal effectors and studied their expression during anthracnose development in maize. Our results demonstrate a strong induction of defense mechanisms occurring in maize cells during C. graminicola infection, even during the biotrophic development of the pathogen. We hypothesize that the switch to necrotrophic growth enables the fungus to evade the effects of the plant immune system and allows for full fungal pathogenicity.
authors.affiliation: Centro Hispanoluso de Investigaciones Agrarias, Department of Microbiology and Genetics, University of Salamanca, 37185 Villamayor, Spain.
authors.forename: Walter A
authors.initials: WA
authors.lastname: Vargas
authors.forename: José M Sanz
authors.initials: JM
authors.lastname: Martín
authors.forename: Gabriel E
authors.initials: GE
authors.lastname: Rech
authors.forename: Lina P
authors.initials: LP
authors.lastname: Rivera
authors.forename: Ernesto P
authors.initials: EP
authors.lastname: Benito
authors.forename: José M
authors.initials: JM
authors.lastname: Díaz-Mínguez
authors.forename: Michael R
authors.initials: MR
authors.lastname: Thon
authors.forename: Serenella A
authors.initials: SA
authors.lastname: Sukno
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000935:Antifungal Agents / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D020231:Colletotrichum / Q000472:pathogenicity*; D003373:Coumaric Acids / Q000378:metabolism; D020869:Gene Expression Profiling; D005800:Genes, Fungal; D017343:Genes, Plant; D054884:Host-Pathogen Interactions; D006861:Hydrogen Peroxide / Q000378:metabolism; D025301:Hyphae / Q000276:immunology / Q000378:metabolism; D010636:Phenols / Q000302:isolation & purification / Q000378:metabolism; D059828:Plant Cells / Q000276:immunology / Q000382:microbiology; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D018515:Plant Leaves / Q000276:immunology / Q000382:microbiology; D011422:Propionates; D017382:Reactive Oxygen Species / Q000378:metabolism; D003313:Zea mays / Q000276:immunology* / Q000382:microbiology*
chemical_list: D000935:Antifungal Agents; D003373:Coumaric Acids; D010636:Phenols; D011422:Propionates; D017382:Reactive Oxygen Species; D000040:Abscisic Acid; D006861:Hydrogen Peroxide; C495469:p-coumaric acid