Moss-pathogen interactions: a review of the current status and future opportunities

Abstract

In complex and diverse environments, plants face constant challenges from various pathogens, including fungi, bacteria, and viruses, which can severely impact their growth, development, and survival. Mosses, representing early divergent lineages of land plants, lack traditional vascular systems yet demonstrate remarkable adaptability across diverse habitats. While sharing the fundamental innate immune systems common to all land plants, mosses have evolved distinct chemical and physical defense mechanisms. Notably, they exhibit resistance to many pathogens that typically affect vascular plants. Their evolutionary significance, relatively simple morphology, and well-conserved defense mechanisms make mosses excellent model organisms for studying plant-pathogen interactions. This article reviews current research on moss-pathogen interactions, examining host-pathogen specificity, characterizing infection phenotypes and physiological responses, and comparing pathogen susceptibility and defense mechanisms between mosses and angiosperms. Through this analysis, we aim to deepen our understanding of plant immune system evolution and potentially inform innovative approaches to enhancing crop disease resistance.

Keywords: disease resistance mechanism; interaction; moss; pathogen; plant immune receptors.

FIGURE 1

Evolutionary distribution of immune-related genes across plant lineages. This figure illustrates the presence and copy number of key immune-related genes across 15 representative plant species, spanning from chlorophytes to angiosperms, with a focus on mosses. The heatmap represents the number of orthologous genes for each immune component (columns) in each species (rows), with darker colors indicating higher copy numbers. Data acquisition and analysis: Genome sequences were obtained from Phytozome (https://phytozome-next.jgi.doe.gov/). The following genome versions were used: Chlamydomonas reinhardtii CC-4532 v6.1, Marchantia polymorpha v3.1, Sphagnum fallax v1.1, Physcomitrium patens v6.1, Selaginella moellendorffii v1.0, Ceratopteris richardii v2.1, Amborella trichopoda v1.0, Nymphaea colorata v1.2, Oryza sativa Kitaake v3.1, Panicum virgatum v5.1, Solanum lycopersicum ITAG5.0, Solanum tuberosum v6.1, Glycine max Wm82. a6. v1, Arabidopsis thaliana Araport11, and Gossypium barbadense v1.1. Orthologous genes were identified using OrthoFinder (Emms and Kelly, 2019).

FIGURE 2

Difference pathways of pathogen sensing between vascular plants and non-vascular plants. Plants sense pathogen-associated molecular patterns (PAMPs) such as FLS2, EFR1, CERK1, and LYK5 through plasma membrane (PM) PRRs (Couto and Zipfel, 2016). Pathogen recognition triggers Ca²⁺production and activates the MAPK cascade (Seybold et al., 2014). P. patens lacks the close relatives of receptors FLS2 and EFR, while a functional CERK1 receptor senses fungal chitin and bacterial peptidoglycan (Bressendorff et al., 2016). Subsequently, at least one MAP kinase kinase (MEKKs), one MAP kinase (MKKs) and two MAP kinases (MPKs) are activated to participate in the defense response of moss to fungal chitin (Bressendorff et al., 2016). ROS, SA and auxin activate the expression of defense genes, leading to the activation of defense mechanisms (De León et al., 2012; De León and Montesano, 2013), including the expression of genes encoding PR proteins, the entry of phenols into cell wall (CW), callose deposition and the accumulation of pre-lignin compounds (Overdijk et al., 2016; De León and Montesano, 2017). HR-like reaction and SAR were also activated in infected mosses (De León et al., 2012). A. thaliana and other angiosperms have receptors such as LYK5, LYK4, CERK1, EFR1 and FLS2 (Couto and Zipfel, 2016), which activate MEKK, MKK and MPKs, leading to the production of ROS and the expression of defense genes (Meng and Zhang, 2013). Hormones SA, JA and OPDA, ABA, auxin and ET activate the expression of defense genes, leading to the activation of defense mechanisms, including PR proteins, phenolic substances into the CW, callose and lignin deposition, HR, SAR and ISR activation (Glazebrook, 2005). The green color is the identified immune-related receptor, and the blue color is the homologous gene of the receptor identified by genomic comparison.