title: Systemic acquired resistance in moss: further evidence for conserved defense mechanisms in plants.
abstract: Vascular plants possess multiple mechanisms for defending themselves against pathogens. One well-characterized defense mechanism is systemic acquired resistance (SAR). In SAR, a plant detects the presence of a pathogen and transmits a signal throughout the plant, inducing changes in the expression of various pathogenesis-related (PR) genes. Once SAR is established, the plant is capable of mounting rapid responses to subsequent pathogen attacks. SAR has been characterized in numerous angiosperm and gymnosperm species; however, despite several pieces of evidence suggesting SAR may also exist in non-vascular plants6-8, its presence in non-vascular plants has not been conclusively demonstrated, in part due to the lack of an appropriate culture system. Here, we describe and use a novel culture system to demonstrate that the moss species Amblystegium serpens does initiate a SAR-like reaction upon inoculation with Pythium irregulare, a common soil-borne oomycete. Infection of A. serpens gametophores by P. irregulare is characterized by localized cytoplasmic shrinkage within 34 h and chlorosis and necrosis within 7 d of inoculation. Within 24 h of a primary inoculation (induction), moss gametophores grown in culture became highly resistant to infection following subsequent inoculation (challenge) by the same pathogen. This increased resistance was a response to the pathogen itself and not to physical wounding. Treatment with β-1,3 glucan, a structural component of oomycete cell walls, was equally effective at triggering SAR. Our results demonstrate, for the first time, that this important defense mechanism exists in a non-vascular plant, and, together with previous studies, suggest that SAR arose prior to the divergence of vascular and non-vascular plants. In addition, this novel moss - pathogen culture system will be valuable for future characterization of the mechanism of SAR in moss, which is necessary for a better understanding of the evolutionary history of SAR in plants.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University, Durham, NC, United States of America.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Winter
authors.affiliation: Indiana University School of Medicine, Indiana University, Muncie, IN, United States of America.
authors.forename: Collin E
authors.initials: CE
authors.lastname: Bowman
authors.affiliation: Department of Biological Sciences, Butler University, Indianapolis, IN, United States of America.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Villani
authors.affiliation: Department of Biological Sciences, Butler University, Indianapolis, IN, United States of America.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Dolan
authors.affiliation: Department of Biological Sciences, Butler University, Indianapolis, IN, United States of America.
authors.forename: Nathanael R
authors.initials: NR
authors.lastname: Hauck
mesh_terms: D019068:Bryopsida / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology*; D060467:Disease Resistance / Q000187:drug effects; D019143:Evolution, Molecular; D054884:Host-Pathogen Interactions / Q000187:drug effects; D010935:Plant Diseases / Q000382:microbiology; D011775:Pythium / Q000502:physiology; D013997:Time Factors; D047071:beta-Glucans / Q000494:pharmacology
chemical_list: D047071:beta-Glucans; C033363:beta-1,3-glucan