Abstract
Anthracnose caused by the hemibiotroph fungus Colletotrichum gloeosporioides is a devastating plant disease with an extensive impact on plant productivity. The process of colonization and disease progression of C. gloeosporioides has been studied in a number of angiosperm crops. To better understand the evolution of the plant response to pathogens, the study of this complex interaction has been extended to bryophytes. The model moss Physcomitrium patens Hedw. B&S (former Physcomitrella patens) is sensitive to known bacterial and fungal phytopathogens, including C. gloeosporioides, which cause infection and cell death. P. patens responses to these microorganisms resemble that of the angiosperms. However, the molecular events during the interaction of P. patens and C. gloeosporioides have not been explored. In this work, we present a comprehensive approach using microscopy, phenomics and RNA-seq analysis to explore the defense response of P. patens to C. gloeosporioides. Microscopy analysis showed that appressoria are already formed at 24 h after inoculation (hai) and tissue colonization and cell death occur at 24 hai and is massive at 48 hai. Consequently, the phenomics analysis showed progressing browning of moss tissues and impaired photosynthesis from 24 to 48 hai. The transcriptomic analysis revealed that more than 1200 P. patens genes were differentially expressed in response to Colletotrichum infection. The analysis of differentially expressed gene function showed that the C. gloeosporioides infection led to a transcription reprogramming in P. patens that upregulated the genes related to pathogen recognition, secondary metabolism, cell wall reinforcement and regulation of gene expression. In accordance with the observed phenomics results, some photosynthesis and chloroplast-related genes were repressed, indicating that, under attack, P. patens changes its transcription from primary metabolism to defend itself from the pathogen.
Highlights
Colletotrichum gloeosporioides is a hemibiotrophic ascomycete fungus that, together with other members of the genus Colletotrichum (C. graminicola, C. lindemuthianum, C. lupini, C.musae), produces anthracnose in many plants [1,2]
Plants under biotic stress activate defense responses mediated by cell surface-localized pattern recognition receptors (PRRs) and intracellular disease resistance proteins, which detect pathogen-associated molecular patterns (PAMPs) and effectors, respectively, leading to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) [7,8]
Safranin-O staining demonstrated that the cell walls were reinforced in response to fungal dissemination (Figure 1I–L), while solophenyl flavine staining revealed that C. gloeosporioides conidia were already germinated at 8 hai and fungal colonization increased at 24 and 48 hai (Figure 1M–P)
Summary
Colletotrichum gloeosporioides is a hemibiotrophic ascomycete fungus that, together with other members of the genus Colletotrichum Studies of fungal–bryophyte interactions at the genomic scale could reveal the molecular mechanisms and ecosystem functioning effects of detrimental or endophytic fungi on metabolite production, nutrient acquisition, plant–pathogen crosstalk and resistance, and abiotic stress alleviation. It could provide insights into the coevolution mechanisms of pathogens with bryophytes and the fungal infection strategies different from those described in vascular plants
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