Pathogenesis in Mosses

Abstract

Physcomitrella patensis an emerging model system for functional studies of plant–pathogen interactions. The ability to create gene knockouts and site‐specific mutations in any gene, coupled with other features, such as dominance of the haploid phase, simple anatomical organization and ease of growth and propagation, allowP. patensto be used as a ‘green yeast’ in experiments with pathogens and pathogen‐derived inducers of the defence response.P. patenshas been shown to be susceptible to a range of necrotrophic bacterial and fungal pathogens, which are able to infect and multiply on the plant. Many of the cellular and molecular responses ofP. patensto attempted infection are similar to those observed in seed plants, and include the production of reactive oxygen species, the synthesis of secondary metabolites, changes in genes expression and the activation of a programmed cell death pathway (PCD). Pathogen‐derived elicitors, toxins and pathogen‐associated molecular patterns (PAMPs) can also induce many of these responses. Gene knockouts confirm that this response is under genetic control and show that this model system can be used to examine other aspects of plant–pathogen interactions. We review our current understanding ofP. patenspathology and defence responses and discuss how this system can be used to study plant defence signaling pathways, and to characterize the functional contributions of defence genes to the expression of disease resistance. We also discuss how genomic and other large‐scale approaches might be used forde novogene discovery in this system.

Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes

“…carotovorum , induce a HR-like reaction (Ponce de León et al, 2007; Reboledo et al, 2015). Typical programmed cell death (PCD) hallmarks are present in elicitor-treated or pathogen-infected moss tissues, including chloroplasts breakdown, accumulation of autofluorescent compounds, cytoplasmic shrinkage, fragmentations of the nucleus and nuclease activities (Ponce de León et al, 2007, 2012; Lawton and Saidasan, 2009). …”

“…Interestingly, cis -OPDA but not JA enhanced HpDTC1 expression and momilactone accumulation, indicating that this oxylipin could regulate momilactone biosynthesis in H. plumaeforme (Okada et al, 2016). The tetracyclic diterpene 16α-hydroxykaurane (Von Schwartzenberg et al, 2004), is produced in P. patens tissues treated with chitosan, and transcripts levels encoding enzymes associated to kaurenes production increase, suggesting that this type of metabolites are also involved in moss defense (Lawton and Saidasan, 2009 ). Taken together, some of these hormonal signaling pathways represent innovations that probably played a role during the adaptation of terrestrial plants to microbial pathogens.…”