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A sensor kinase controls turgor-driven plant infection by the rice blast fungus

Abstract

The blast fungus Magnaporthe oryzae gains entry to its host plant by means of a specialized pressure-generating infection cell called an appressorium, which physically ruptures the leaf cuticle1,2. Turgor is applied as an enormous invasive force by septin-mediated reorganization of the cytoskeleton and actin-dependent protrusion of a rigid penetration hypha3. However, the molecular mechanisms that regulate the generation of turgor pressure during appressorium-mediated infection of plants remain poorly understood. Here we show that a turgor-sensing histidine–aspartate kinase, Sln1, enables the appressorium to sense when a critical turgor threshold has been reached and thereby facilitates host penetration. We found that the Sln1 sensor localizes to the appressorium pore in a pressure-dependent manner, which is consistent with the predictions of a mathematical model for plant infection. A Δsln1 mutant generates excess intracellular appressorium turgor, produces hyper-melanized non-functional appressoria and does not organize the septins and polarity determinants that are required for leaf infection. Sln1 acts in parallel with the protein kinase C cell-integrity pathway as a regulator of cAMP-dependent signalling by protein kinase A. Pkc1 phosphorylates the NADPH oxidase regulator NoxR and, collectively, these signalling pathways modulate appressorium turgor and trigger the generation of invasive force to cause blast disease.

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Fig. 1: Reducing appressorium turgor prevents septin-ring formation and impairs blast infection.
Fig. 2: Identification of the Sln1 turgor-sensing kinase in M. oryzae.
Fig. 3: Characterization of the Sln1 turgor-sensing complex in M. oryzae.
Fig. 4: Model of turgor-driven invasion of a plant cell by the rice blast fungus.

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Data availability

All strains generated and datasets analysed during the current study, including codes and algorithms, are available either in public repositories as stated, or from the corresponding author on reasonable request.

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Acknowledgements

We acknowledge technical support from O. Goode and T. Penn. This work was funded by a European Research Council (ERC) Advanced Investigator Award to N.J.T. under the European Union’s Seventh Framework Programme (FP7/2007-2013), ERC grant no. 294702 GENBLAST. L.S.R. acknowledges the late P. Ryder for support and encouragement.

Author information

Authors and Affiliations

Authors

Contributions

L.S.R., Y.F.D. and N.J.T. conceived and designed the project. L.S.R., Y.F.D., M.J.K., M.O.-R., N.C.-M. and X.Y. performed experimental work. D.M.S. performed bioinformatic analysis. C.V., A.M. and V.S. performed mathematical modelling. F.L.H.M., N.C.-M. and J.S. performed proteomic analysis. L.S.R. and N.J.T. wrote the paper with assistance and input of coauthors.

Corresponding author

Correspondence to Nicholas J. Talbot.

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Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Peer review information Nature thanks Antonio Di Pietro, Nicholas Money and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Fig. 1 Application of glycerol to intact rice leaves does not cause cell collapse.

a, Micrographs showing epidermal strips of a transgenic rice line that expresses the plasma-membrane marker Lti6B–GFP, treated with either water or glycerol (5 M) for 24 h. Treatment with glycerol caused cell collapse. b, Intact leaves from 2-week-old Lti6B–GFP transgenic rice plants were inoculated with 30-μl drops of water or 5 M glycerol and incubated for 3 days. No plasmolysis was observed; that is, glycerol was unable to cause the collapse of cells in whole plants. c, Rice plants were treated with water or 5 M glycerol spray and incubated for 5 days (n = 3 independent replications of the experiment). Glycerol did not have any effect on the health of the rice plant or cause any wilting—confirming that no plasmolysis of rice cells from intact leaves occurs (as shown in b). Micrographs are representative of two independent replicates of the experiment. Scale bars, 20 μm (a); 5 μm (b).

Extended Data Fig. 2 Septin organization is impaired by artificial lowering of turgor or inhibition of melanin biosynthesis.

a, Percentage of appressoria that have intact septin rings after treatment with 1.5 M glycerol or 100 µM tricyclazole. Treatments were applied between 0 and 20 h.p.i and quantified at 24 h.p.i. A window of effect could thus be defined for reaching the threshold of appressorium turgor (by 16–20 h.p.i.) and for completion of melanization (by 12 h.p.i. Data are mean ± s.d. for n = 3 independent biological replicates; 100 appressoria were counted per replicate. ****P < 0.0001,***P < 0.001, **P < 0.01 (two-tailed unpaired Student’s t-test compared to untreated Guy11 control). b, Percentage of appressoria that have intact septin GTPase and F-actin rings in wild-type Guy11 and the melanin-deficient mutants Δalb1, Δrsy1 and Δbuf1 at 24 h.p.i. Data are mean ± s.d. for n = 3 independent biological replicates; 100 appressoria were counted per replicate.

Extended Data Fig. 3 Characteristics of the Sln1 turgor-sensor kinase.

a, Graphical simulation of a mathematical model for appressorium function in M. oryzae. The model assumes that septins are recruited to the appressorium pore at a seeded ring structure that allows the recruitment of F-actin. Melanin is recruited to the appressorium dome in proportion to increasing turgor, and excluded from the pore. A turgor sensor (TS) is recruited to the pore to modulate melanization and turgor generation, while positively regulating septin recruitment and F-actin reorganization; this results in cuticle rupture (Supplementary Video 1). b, A mutant that lacks the turgor sensor generates excess appressorium turgor, recruits more melanin to the cell wall and prevents the recruitment of septin and F-actin to the pore; the cuticle is therefore not breached (Supplementary Video 2). c, Micrographs showing that the Δsln1 mutant is unable to invade and colonize rice tissue after 36 h.p.i. No invasive hyphae were visualized inside rice cells inoculated with Δsln1. Images are representative of n = 2 independent biological replicates. Scale bar, 10 µm. d, Localization of Sln1–GFP in conidia and appressoria of M. oryzae. Conidia were collected from a M. oryzae Guy11 transformant that expresses a Sln1–GFP gene fusion, and inoculated on glass coverslips. Images were captured at 0, 4, 6, 8 and 24 h.p.i. Micrographs are representative of the distribution of Sln1–GFP at the indicated time points in n = 3 independent biological replications of the experiment. Scale bars, 10 µm. e, Epifluorescence micrographs showing that the cellular distribution of H1–GFP in appressoria at 24 h.p.i. is unaffected by exposure of appressoria to 1.5 M glycerol at 5 h.p.i. Images are representative of n = 3 independent biological replicates; 50 appressoria were counted per replicate. Scale bar, 10 µm.

Extended Data Fig. 4 Deposition of melanin in appressoria increases in a dose-dependent manner after exposure to hyperosmotic stress.

Conidia were collected from the Guy11 strain and inoculated on glass coverslips. Glycerol solutions of different concentrations (ranging from 0.25 to 2.5 M) were applied 3–4 h.p.i. and the appressoria were imaged by bright-field microscopy at 24 h.p.i. to visualize the melanin layer in the appressorium. Artificially lowering turgor by application of hyperosmotic stress led to continual melanization of the appressorium—consistent with melanin biosynthesis and cell-wall deposition being turgor-dependent. Images are representative of n = 2 independent biological replications of the experiment. Scale bar, 10 µm.

Extended Data Fig. 5. Melanin biosysnthesis and cytoskeletal organization is affected in Δsln1 mutants.

a, Transcript abundance of genes that are involved in DHN-melanin biosynthesis in a Δsln1 mutant compared to Guy11 in appressoria at 16 h.p.i. Gene expression is represented as base mean expression from n = 3 three RNA-seq experiments. ****P < 0.0001 (two-tailed unpaired Student’s t-test). b, Sln1 is required for the septin-mediated reorganization of F-actin at the appressorium pore. Conidia were collected from Guy11 transformants that express Septin3–GFP, Septin5–GFP, LifeAct–RFP, gelsolin–GFP, Chm1–GFP and Tea1–GFP gene fusions, inoculated on glass coverslips and observed by epifluorescence microscopy at 24 h.p.i. The proportion of appressoria that have intact rings was recorded. Data are mean ± s.d. for n = 3 independent biological replicates; 50 appressoria were counted per replicate. ****P < 0.0001, **P < 0.01 (two-tailed unpaired Student’s t-test). c, Septin5–GFP is not recruited to the appressorium pore in a melanin-deficient Δalb1 mutant. Conidia were collected from Guy11 and Δalb1 transformants that express Sep5–GFP, inoculated on glass coverslips and observed by epifluorescence microscopy at 6, 8 and 20 h.p.i. The distribution of Sep5–GFP at the cell cortex or appressorium pore was recorded. Images are representative of n = 3 independent biological replicates. Scale bar, 10 µm.

Extended Data Fig. 6 Mechanosensitive ion channels are required for appressorium formation but dispensable for septin-mediated cytoskeletal reorganization.

a, Conidia were collected from Guy11 and inoculated on glass coverslips in the presence and absence of gadolinium (Gd+3). Appressoria were imaged by bright-field microscopy at 24 h.p.i. Addition of gadolinium disrupted appressorium formation. Images are representative of n = 3 independent biological replications of the experiment. b, Micrographs showing the cellular localization of Sep5–GFP at the appressorium pore of Guy11 after treatment with gadolinium or verapamil at 0–20 h.p.i., imaged at 24 h.p.i. Images are representative of n = 3 independent biological replicates. Scale bars, 10 μm (a, b). c, Percentage of appressoria that have intact septin rings after treatment with gadolinium and verapamil. Data are mean ± s.d. for n = 3 independent biological replicates; 100 appressoria were counted per replicate. **P < 0.01 (two-tailed unpaired Student’s t-test).

Extended Data Fig. 7 Mechanosensitive ion channels are dispensable for pathogenicity.

a, Schematic representation of the split-marker method that was used to generate targeted deletions of genes that encode mechanosensitive ion channels, LF denotes left flank and RF denotes right flank as regions flanking the open reading frame for the gene of interest. Primers are shown in Supplementary Table 1. Deletion mutants were identified by Southern blot analysis (for gel source data of the Δmic1, Δmic2 and Δmic3 gene-deletion digests for Southern blotting, see Supplementary Fig. 1a, b and c, respectively). b, Dot plot showing the frequency of disease lesions observed in a 5-cm zone from each individual leaf harvested per strain (60 leaves were harvested per strain). Data are the mean and individual data points for n = 2 independent biological replicates. Each data point represents the number of lesions on an infected rice leaf. P > 0.01 (two-tailed, unpaired Student’s t-test with Welch-correction, compared to a Guy11 control). c, Micrographs showing the cellular localization of Mic2–GFP at the appressorium pore of Guy11 and Δsln1 at 24 h.p.i. Images are representative of n = 3 independent biological replicates. Scale bar, 10 μm.

Extended Data Fig. 8 Chitin deposition in the appressorium cell wall is impaired in a Δsln1 mutant.

a, Conidia were collected from Guy11 and the Δsln1 mutant and inoculated on glass coverslips to form appressoria. At 24 h.p.i., appressoria were stained with 50 µM calcofluor white for 5 min in the dark, washed and images captured by epifluorescence microscopy. Line-scan graphs represent calcofluor white fluorescence in a transverse section of an individual appressorium. Images are representative of n = 3 independent biological replicates. Scale bar, 10 µm. b, The Sln1 kinase interacts with Sum1, Pkc1 and Mps1 in a yeast two-hybrid assay. Simultaneous co-transformation of pGAD-Sln1 (prey vector) with pGBK-Mps1, pGBK-PKC and pGBK-Sum1 (bait vectors) and pGBKT7-53 and pGADT7-T (positive-control vectors) into the Y2H Gold strain resulted in the activation of three reporter genes and growth on medium-stringency medium (−Ade, −Leu, –Trp, +X-α-gal). Co-transformation also activates the expression of MEL1, which results in the secretion of α–galactosidase and the hydrolysis of X-α-gal in the medium, turning the yeast colonies blue. Images are representative of n = 2 biological replications of the experiment.

Extended Data Fig. 9 The PKA inhibitor H-89 disrupts gelsolin ring assembly.

a, Micrographs showing the cellular localization of gelsolin–GFP at the appressorium pore of Guy11 after treatment with the PKA inhibitor H-89 at 6 h.p.i. and 8 h.p.i., imaged at 24 h.p.i. Images are representative of n = 3 independent biological replications of the experiment. Scale bar, 10 μm. b, Percentage of appressoria that have intact gelsolin rings after treatment with H-89. Data are mean ± s.d. for n = 3 independent biological replicates; 50 appressoria were counted per replicate. ****P < 0.0001 (two-tailed unpaired Student’s t-test). c, Percentage of appressoria that have intact gelsolin and septin rings in Guy11 and the Δcpka mutant. Rings were routinely smaller in Δcpka than in Guy11, indicating the reduced diameter of the appressorium in the Δcpka mutant. Data are mean ± s.d. for n = 3 independent biological replicates; 50 appressoria were counted per replicate. ****P < 0.0001 (two-tailed unpaired Student’s t-test).

Extended Data Fig. 10 Interplay between the cell integrity and cAMP-dependent protein kinase A pathways in turgor sensing by the rice blast fungus.

a, Inhibition of Pkc1 activity with 1NA-PP1 can be reversed to restore septin and gelsolin ring formation. Micrographs showing the cellular localization of Sep5–GFP and gelsolin–GFP at the appressorium pore following Pkc1 blocking at 10 h.p.i. and releasing at 13 h.p.i. Appressoria were imaged at 24 h.p.i. Images are representative of n = 2 replications of the experiment. b, Heat map showing the expression of NOX1, NOX2 and NOXR in an RNA-seq analysis of the PKC1AS-mutant. Mycelium was grown in CM shake cultures for 48 h in the presence or absence of 500 nM 1NA-PP1 at 1, 3, 6, 12 or 24 h.p.i. (n = 3 biological replications of the experiment). The full RNA‐seq dataset from this study can be found at the Gene Expression Omnibus (GEO) under accession number GSE70308. c, Pkc1 interacts with Nox2 and NoxR in a yeast two-hybrid assay. Simultaneous co-transformation of pGBK-PKC (bait vector) and pGAD-Nox2 and pGAD-NoxR (prey vectors) into the Y2H Gold strain resulted in the activation of three reporter genes and growth on medium-stringency medium for Pkc1 and NoxR (−His, −Leu, –Trp, +X-α-gal), and on high-stringency medium for Pkc1 and Nox2 (–His, −Leu, −Trp, −Ade, +X-α-gal). Co-transformation also activates the expression of MEL1, which results in the secretion of α–galactosidase and the hydrolysis of X-α-gal in the medium, turning the yeast colonies blue. Images are representative of n = 3 independent biological replications of the experiment. d, Alignment of a region of the predicted amino acid sequence of NoxR using Muscle40. Sequence conservation is shaded in grey, with a consensus threshold of 75%. The predicted Pkc1 phosphorylation site is marked with a red arrow and is highly conserved; black arrows indicate other potential Pkc1 phosphorylation targets based on the motif S*APS. e, ΔpdeH mutants generate excess appressorium turgor. Percentage of Guy11 and ΔpdeH-mutant appressoria that undergo incipient cytorrhysis after exposure to glycerol solutions of 0–3.5 M. Data are mean ± s.e.m. for n = 3 independent biological replicates; 50 appressoria were counted per replicate. **P < 0.01 (two-tailed unpaired Student’s t-test). f, Cellular localization of Sln1–GFP in appressorium pores of Guy11, with or without hydroxyurea (HU) added at 6 h.p.i and imaged at 24 h.p.i. Images are representative of n = 3 independent biological replicates. Scale bars, 10 µm.

Supplementary information

Supplementary Information

Supplementary Information Mathematical Model. This file presents a full description of a geometric partial differential mathematical model for appressorium-mediated plant infection by the rice blast fungus Magnaporthe oryzae. The model links evolution of the appressorium with a system of reaction-diffusion equations to describe the spatio-temporal dynamics of the molecular components of the appressorium that control its turgor-driven infection mechanism. The file includes two Supplementary Information Figures and three Supplementary Information Tables with a full guide.

Reporting Summary

Supplementary Data

Source Data Figure 1 shows original uncropped autoradiographs and corresponding electrophoresis gel images for the targeted gene deletion experiments presented in Extended Data Figure 7a.

Supplementary Table

Supplementary Table 1 shows all DNA oligonucleotide primers used in the study.

Supplementary Table

Supplementary Table 2 shows a summary of in vivo phosphorylation sites on potential PKC1 targets identified by LC-MS/MS analysis.

Video 1

The video shows a simulation of appressorium-mediated plant infection based on the mathematical model. The simulation shows septin-dependent actin re-organisation, melanin deposition and the relation to turgor generation, force generation and re-polarisation.

Video 2

Simulation of appressorium in a predicted turgor sensor mutant. The mathematical model was run in the absence of the postulated turgor sensor, so that the characteristics of a mutant lacking this molecular component could be investigated. The model predicted excess turgor generation and impairment in re-polarisation would occur in a turgor-sensor mutant.

Video 3

Laser confocal image of Sln1-GFP localisation. Conidia were harvested from a M. oryzae Guy11 transformant expressing a Sln1-GFP gene fusion and inoculated onto glass coverslips. Three dimensional maximum projection z-stack images were captured at 24hpi using a Leica SP8 laser confocal microscope.

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Ryder, L.S., Dagdas, Y.F., Kershaw, M.J. et al. A sensor kinase controls turgor-driven plant infection by the rice blast fungus. Nature 574, 423–427 (2019). https://doi.org/10.1038/s41586-019-1637-x

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