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.

Signals of Systemic Immunity in Plants: Progress and Open Questions

“…Systemic acquired resistance (SAR) is an inducible defence mechanism that provides protection in distant, pathogen-free parts of plants against a broad range of pathogens. In practice, SAR has been recognised as a strategy to control plant pathogens because of its stability [ 1 ], long-lasting effectiveness [ 2 ], and transgenerational effect [ 3 ]. In the latter case, defence mechanisms are induced faster in the progeny after pathogen infection.…”

Manipulation of Bryophyte Hosts by Pathogenic and Symbiotic Microbes

“…In bryophytes, several changes in host subcellular organization are observed during interactions with symbiotic or pathogenic microbes. In moss, filamentous necrotrophic pathogens induce cytoplasmic shrinkage as well as chloroplast repositioning and degradation, which ultimately leads to cell death ( Davey et al 2009 , Oliver et al 2009 , Ponce de Leon 2011 , Lehtonen et al 2012 , Winter et al 2014 , Yan et al 2017 ). In comparison, interactions between P. patens and the hemi-biotrophic pathogen P. capsici are associated with the accumulation of cytoplasm and the repositioning of actin filaments and nuclei towards sites of hyphal invasion ( Overdijk et al 2016 ).…”

Comparative transcriptome profile of the leaf elongation zone of wild barley (Hordeum spontaneum) eibi1 mutant and its isogenic wild type

“…The use of an inducible defense system, named acquired resistance (AR) has been well demonstrated in plants ( Heath, 2000 ; Conrath, 2006 ; Winter et al , 2014 ). AR or systemic acquired resistance (SAR) is a form of inducible resistance that is triggered systemically in plants.…”