Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes

Abstract

Bryophytes, including mosses, liverworts and hornworts are early land plants that have evolved key adaptation mechanisms to cope with abiotic stresses and microorganisms. Microbial symbioses facilitated plant colonization of land by enhancing nutrient uptake leading to improved plant growth and fitness. In addition, early land plants acquired novel defense mechanisms to protect plant tissues from pre-existing microbial pathogens. Due to its evolutionary stage linking unicellular green algae to vascular plants, the non-vascular moss Physcomitrella patens is an interesting organism to explore the adaptation mechanisms developed in the evolution of plant defenses to microbes. Cellular and biochemical approaches, gene expression profiles, and functional analysis of genes by targeted gene disruption have revealed that several defense mechanisms against microbial pathogens are conserved between mosses and flowering plants. P. patens perceives pathogen associated molecular patterns by plasma membrane receptor(s) and transduces the signal through a MAP kinase (MAPK) cascade leading to the activation of cell wall associated defenses and expression of genes that encode proteins with different roles in plant resistance. After pathogen assault, P. patens also activates the production of ROS, induces a HR-like reaction and increases levels of some hormones. Furthermore, alternative metabolic pathways are present in P. patens leading to the production of a distinct metabolic scenario than flowering plants that could contribute to defense. P. patens has acquired genes by horizontal transfer from prokaryotes and fungi, and some of them could represent adaptive benefits for resistance to biotic stress. In this review, the current knowledge related to the evolution of plant defense responses against pathogens will be discussed, focusing on the latest advances made in the model plant P. patens.

The coming of age of EvoMPMI: evolutionary molecular plant–microbe interactions across multiple timescales

“…Terrestrial plants are thought to have evolved as the result of an ancient symbiosis between a semi-aquatic green alga and an aquatic fungus, borne onto land over 450 millennia ago [1]. In this model, the colonization of land by plants-and therefore their very evolution-was only possible through an intimate partnership with a filamentous microorganism [2][3][4].…”

“…The rationale is that comparative studies with a range of land plants will shed light on ancestral features of plant-microbe interactions. It turns out that many microbial pathogens can infect bryophytes, causing disease symptoms such as necrosis and tissue maceration [2]. The oomycete Phytophthora palmivora was shown to colonize the photosynthetic layer of liverworts-the earliest diverging land plant-and to form intracellular hyphal structures similar to the haustoria produced on angiosperms [3] (Figure 1b).…”

Differential gene expression associated with fungal trophic shifts along the senescence gradient of the moss Dicranum scoparium

“…Generally, mosses are observed to lack fungal symbionts such as mycorrhizal fungi (Field et al, 2015), but studies during the last decade have consistently reported that they host rich fungal communities Currah, 2006, 2007;Stenroos et al, 2010;U'Ren et al, 2010U'Ren et al, , 2012. Despite the uncertainty about the phylogenetic relationships among bryophytes and their affiliations to tracheophytes (Puttick et al, 2018), fungal interactions with early diverging land plants could unveil ancestral genetic mechanisms associated with the origin of fungal endophytism (Delaux et al, 2013;Ponce de León and Montesano, 2017;Lutzoni et al, 2018). Perennial mosses can have a natural senescence gradient that is ideal to study the functions of fungal endophytes and their life cycles.…”

Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage

“…Unfortunately, our understanding of plant-pathogen interactions in these plants is extremely limited. In comparison, several groups have described pathogenic interactions in the model moss Physcomitrella patens [21-23]. The colonization of moss tissues is associated with intracellular hyphal growth, however specialized infection structures similar to haustoria are not observed within moss cells [22].…”