Appressorium-mediated plant infection by Magnaporthe oryzae is regulated by a Pmk1-dependent hierarchical transcriptional network

Abstract

ice blast disease is an important threat to global food security 1 . The disease starts when asexual spores of Magnaporthe oryzae, called conidia, land on the hydrophobic surface of a rice leaf inducing differentiation of an infection cell called an appressorium 1-3 . The appressorium develops turgor of up to 8.0 MPa due to glycerol accumulation, which generates osmotic pressure 4 . Glycerol is maintained in the appressorium by melanin in the cell wall, which reduces its porosity 4,5 . Development of the appressorium is tightly linked to the cell cycle, autophagy [6][7][8] and metabolic checkpoint control mediated by TOR kinase and the cAMP-dependent protein kinase A (PKA) pathway [9][10][11] . Appressorium turgor is monitored by a sensor kinase, Sln1, and once a threshold is reached 12 , septin GTPases in the appressorium pore form a hetero-oligomeric complex that scaffolds cortical F-actin at the base of the appressorium 13,14 . This leads to force generation to pierce the cuticle with a rigid penetration hypha. Once inside the leaf, invasive hyphae colonize the first epidermal cell before seeking out plasmodesmata-rich pit fields through which the fungus invades neighbouring cells 15 . M. oryzae actively suppresses plant immunity using fungal effector proteins delivered into plant cells 16 . After five days, disease lesions appear from which the fungus sporulates to colonize neighbouring plants.Formation of an appressorium by M. oryzae requires a conserved pathogenicity mitogen-activated protein kinase (MAPK), called Pmk1 (ref. 17 ). Pmk1 mutants cannot form appressoria or cause plant infection, even when plants are wounded 17 . Instead, Δpmk1 mutants produce undifferentiated germlings that undergo several rounds of mitosis and septation 17,18 . Pmk1 is also responsible for lipid and glycogen mobilization to the appressorium, autophagy in the conidium 4,8,19,20 and invasive cell-to-cell movement 15 . A set of pl surface sensors 21 that trigger cAMP-PKA signalling are required for Pmk1 activation 17 , and a TOR-dependent nutrient sensing pathway is necessary for appressorium formation, acting upstream, or perhaps independently, of Pmk1 (refs. [9][10][11] ). The mechanism by which Pmk1 exerts such an important role in plant infection has remained largely unknown and only one transcriptional regulator, Mst12, which may act downstream of Pmk1, has been characterized in detail. Mst12 mutants form appressoria normally but are non-functional and cannot cause disease 22 .In this study we set out to identify the mechanism by which major transcriptional changes are regulated during appressorium development by M. oryzae. We identified major temporal changes in gene expression in response to an appressorium-inductive hydrophobic

The transcriptional landscape of plant infection by the rice blast fungus Magnaporthe oryzae reveals distinct families of temporally co-regulated and structurally conserved effectors

“…M7 shows genes which peak in expression during appressorium development at 8 h and then again during transpressorium development at 48h. This observation is consistent with the developmental conservation of these two infection structures, as recently highlighted (Cruz-Mireles et al, 2021). M7 contains MST12, for example, which encodes a transcription factor required for appressorium-mediated penetration (Park et al, 2002), CPKA encoding the catalytic sub-unit of cAMP-dependent protein kinase A, another key regulator of appressorium development (Mitchell and Dean, 1995), as well as the cell cycle regulator NIM1 (Saunders et al, 2010) and peroxin-encoding gene PEX1 (Deng et al, 2016).…”

Efficacy and Mechanism of Thymol/KGM/LG Edible Coating Solution on Inhibition of Mucor circinelloides Isolated From Okra

“…Polygalacturonase (PG) and cellulase (Cx) are fungal metabolites that could promote degradation of the plant cell wall, resulting in plant cell damage and disease generation ( Pandaranayaka et al, 2019 ; Osés-Ruiz et al, 2021 ). As can be seen from the figure, the activity of PG decreased significantly after the treatment with TK100 throughout the whole culture cycle, especially after treatment for 60 h ( Figure 6D ), the activity of PG decreased by 18.7% compared with the control group ( p < 0.05).…”

Mitogen-Activated Protein Kinase CsPMK1 Is Essential for Pepper Fruit Anthracnose by Colletotrichum scovillei

“…Orthologs of CsHOX7 were reported to regulate appressorium formation in several plant pathogenic fungi ( Kim et al, 2009 ; Yokoyama et al, 2018 ; Fu et al, 2021 ). Recently, Pmk1 was demonstrated to regulate appressorium formation via phosphorylation of MoHOX7 in M. oryzae ( Osés-Ruiz et al, 2021 ). The CsHOX7 was also found to interact with CsPMK1, based on the result of a Y2H assay ( Figure 8A ).…”