• Korean Journal Plant Pathology
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• v.14 no.5
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• pp.413-417
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• 1998

Magnaporthe grisea, the casual agent of rice blast, requires formation of an appressorium, a dome-shaped and well melanized infection structure, to penetrate its host. Environmental cues that induce appressorium formation include hydrophobicity and hardness of contact surface and chemicals from its host. Artificial surfaces are widely used to induce appressorium formation, but frequencies of appressorium induction are not always consistent. To understand variable induction of appressorium formation in M. grisea, several factors were tested on GelBond. High levels of appressorium formation were induced over a wide range of temperature (20~3$0^{\circ}C$) and pH (4~7). spore age up to 3-week-old did not significantly affect appressorium formation, but only a few apressoria on GelBond. However, adenosine specifically inhibited appressorium formation. Adenosine inhibition of appressorium formation was restored by exogenous addition of cAMP. Germ tube tips of M. grisea maintained the ability to differentiate appressoria by chemical inducers on GelBond at least up to 16 h after conidia germination. These results suggest that environmental factors have little effect on the variable induction of appressorium formation on the artificial surface in M. grisea.

• The Plant Pathology Journal
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• v.27 no.3
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• pp.225-231
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• 2011

Previously, we identified the 20S proteasome ${\alpha}$-subunit of Magnaporthe oryzae (M. oryzae) induced during appressorium formation, and detected an increase in multiple protein ubiquitination during the early appressorium formation process (Kim et al., 2004). In this study, we further attempted to determine whether the proteasome is involved in the appressorium formation of M. oryzae both in vitro and in planta, using proteasome inhibitors. A significant increase in 20S proteasome during fungal germination and appressorium formation was observed using Western blot analysis with 20S proteasome antibody, demonstrating that proteasome-mediated protein degradation was involved in appressorium formation. Pharmacological analysis using proteasome inhibitors, MG-132, proteasome inhibitor I (PI) and proteasome inhibitor II (PII) revealed that germination and appressorium formation were delayed for 4 to 6 h on rice leaf wax-coated plates. Similarly, the treatment of proteasome inhibitors with fungal conidia on the rice leaf surface delayed appressorium formation and host infection processes as well. Additionally, fungal pathogenicity was strongly reduced at 4 days' postfungal infection. These data indicated that the fungal 20S proteasome might be involved in the pathogenicity of M. oryzae by the suppression of germination and appressorium formation.

• Journal of Microbiology and Biotechnology
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• v.17 no.7
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• pp.1198-1203
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• 2007

Conidial adhesion and appressorium formation of Magnaporthe oryzae on the rice surface are important early events in the infection process. As an initiative step to understand the mechanisms underlying these cellular processes at a biochemical level, the effect of a human fibronectin antibody (HFA) and RGD peptides on conidial adhesion and appressorium formation was evaluated. HFA inhibited conidial adhesion and appressorium formation in a dosage-dependent manner. RGD peptides also inhibited these cellular events. Conidial adhesion and appressorium formation inhibited by RGD peptides were restored by chemicals involved in the cyclic AMP-dependent signaling pathway. These results suggest that extracellular matrix proteins might be involved in conidial adhesion and appressorium formation through integrin-like receptor mediation and modulation of cAMP-dependent signaling in the cells.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.84.1-84
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• 2003

Magnaporthe grisea, the casual agent of rice blast, forms an appressorium to penetrate its host. Much has been learned about environmental cues and signal transduction pathways, especially those involving CAMP and MAP kinases, on appressorium formation during the last decade. More recently, pharmacological data suggest that calcium/calmodulin-dependent signaling system is involved in its appressorium formation. To determine the role of phosphoinositide-specific phospholipase C (PI-PLC) on appressorium formation, a gene (WPLCl) encoding PI-PLC was cloned and characterized from M. grisea strain 70-15. Sequence analysis showed that MPLCl has alt five conserved domains present in other phospholipase C genes from several filamentous fungi and mammals. Null mutants (mplcl) generated by targeted gene disruption exhibited pleiotropic effects on conidial morphology, appressorium formation, fertility and pathogenicity. mplcl mutants developed nonfunctional appressoria and are also defective in infectious growth in host tissues. Defects in appressorium formation and pathogenicity in mplcl mutants were complemented by a mouse PLCdelta-1 cDNA under the control of the MPLCl promoter. These results suggest that cellular signaling mediated by MPLCl plays crucial and diverse roles in development and pathogenicity of M. grisea, and functional conservation between fungal and mammalian Pl-PLCs.

• The Korean Journal of Mycology
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• v.15 no.3
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• pp.142-148
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• 1987

The results investigated of the effect of light, pH, and nutrients in vitro and the levels of fertilizer(P,K and Ca) in vivo in order to find out the effect of environmental factors in forming an appressorium of Colletotrichum truncatum were as follows; The ratio of appressorium formation promoted more in a light treatment than in a dark treatment according to investigation after three and six hours passed away. But after the period, the ratio of appressorium formation promoted highly in both treatments. Reasonable pH of appressorium formation was pH 6-pH 8. The ratio of appressorium formation was the most favorable at none nutrient level in every treatment of C-source and N-source, and suppressed in a high concentration of C-source and N-source. But according as the time passed away, the ratio of appressorium formation promoted in C-source and N-source. When their quantities were increased in P and K treatments, the ratio of appressorium formation was somewhat suppressed but it was highly suppressed in the gradual order of none fertilizer level < standard fertilizer level < doubled fertilizer level in Ca treatment according to investigation after the first three hours passed away. But after the period, the ratio of appressorium formation promoted highly regardless of the level of fertilizer.

• The Plant Pathology Journal
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• v.21 no.4
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• pp.322-327
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• 2005

Regression models for determining infection periods of apple white rot were developed based on conidial germination and appressorium formation of Botryosphaeria dothidea. A total of 120 apple fruits were inoculated with the fungal conidial suspension and subjected to 6 temperatures and 10 wetness periods. Conidia germinated and produced appressoria, exhibiting swollen tips of germ tubes on the fruit surface. Conidial germination (G) increased with temperature (T) and wetness period (W), and was described as $G=-89.273+7.649T+7.056W-0.109T^{2}-0.085W^{2}-0.066TW(R^{2}=0.75)$. Less than 2 hr of wetness period were enough for conidia to germinate at 25 to $30^{\circ}C$. Effects of temperature and wetness period on appressorium formation (A) could be explained as $A=-1.540-2.375W+0.045W^{2}+0.213TW(R^{2}=0.77)$. The relationship between conidial germination and appressorium formation ($A_g$) was described as$A_g=0.381-0.227G+0.005G^{2}(R^{2}=0.67)$, suggesting that conidial germination may have to reach approximately $43.7\%$ to initiate appressorium formation. Using the regression equation for conidial germination and the criterion of $43.7\%$ conidial germination, an infection model was developed to determine infection periods based on temperature and wetness period. The infection model with the criterion of $43.7\%$ conidial germination was apparently more conservative than the appressorium formation model in determining possibility of apple infection. The infection model seemed sensitive to variable weather conditions, suggesting possible use of the model for timing fungicide sprays to control white rot of apples in practice.

• Korean Journal Plant Pathology
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• v.10 no.4
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• pp.254-260
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• 1994

Magnaporthe grisea, a causal agent of blast, forms a specialized infection structure, an appressorium, to infect host. Hydrophobicity of contact surface and cAMP have been suggested as a primary environmental signal and a second messenger to trigger and mediate appressorium formation in this fungus, respectively. To generalize these factors in field isolates of M. girsea, twenty isolates originated from rice and other gramineous hosts were tested. Seventeen including rice and non-rice isolates formed appressoria on hydrophobic surface, but none of isolates formed appressoria on hydrophilic surface. Eighteen isolates formed appressoria on hydrophilic surface in the presence of IBMX, an inhibitor of phosphodiesterase, except two rice isolates. These results strongly support the hypothesis that appressorium formation by M. grisea is induced by hydrophobic hard surface and regulated by the endogenous level of cAMP in the cells. Understanding fungal development is not only of biological interest but provides new targets for novel disease control strategies.

• Research in Plant Disease
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• v.25 no.4
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• pp.205-212
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• 2019

Analysis of differentially expressed genes has assisted discovery of gene sets involved in particular biological processes. The purpose of this study was to identify genes involved in appressorium formation in the rice blast fungus Magnaporthe oryzae via analysis of cDNA-amplified fragment length polymorphisms. Amplification of appressorial and vegetative mycelial cDNAs using 28 primer combinations generated over 200 differentially expressed transcript-derived fragments (TDFs). TDFs were excised from gels, re-amplified by PCR, cloned, and sequenced. Forty-four of 52 clones analyzed corresponded to 42 genes. Quantitative real-time PCR showed that expression of 23 genes was up-regulated during appressorium formation, one of which was the MCK1 gene that had been shown to be involved in appressorium formation. This study will be providing valuable resources for identifying the genes such as pathogenicity-related genes in M. oryzae.

• The Plant Pathology Journal
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• v.19 no.1
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• pp.34-42
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• 2003

The ascomycete Magnaporthe grisea is a pathogen of rice blast and is known to form specialized infection structures called appressoria for successful infection into host cells. To understand the molecular mechanism underlying infection process, appressorium-related genes were identified through global approaches including EST sequencing, differential hybridization, and sup-pression subtractive hybridization. EST database was generated on >2,000 cDNA clones randomly selected from appressorium stage cDNA library. Large number of ESTs showed homology to known proteins possibly involved in infection-related cellular development (attachment, germination, appressorium formation, and colonization) of rice blast fungus. The 1051 ESTs showing significant homology to known genes were assigned to 11 functional categories. Differential hybridization and suppression subtractive hybridization were applied to identify genes showing an appressorium stage specific expression pattern. A number of genes were selected as up-regulated during appressorium formation compared with the vegetative growing stage. Clones from various cDNA libraries constructed in different developmental stages were arrayed on slide glass for further expression profiling study. functional characterization of genes identified from these global approaches may lead to a better understand-ing of the infection process of this devastating plant disease, and the development of novel ways to protect host plant.

• The Plant Pathology Journal
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• v.26 no.1
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• pp.17-24
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• 2010

A logistic model for describing combined effects of both temperature and wetness period on appressorium formation was developed using laboratory data on percent appressorium formation of Colletotrichum acutatum. In addition, the possible use of the logistic model for forecasting infection risks was also evaluated as compared with a first-order linear model. A simplified equilibrium model for enzymatic reactions was applied to obtain a temperature function for asymptote parameter (A) of logistic model. For the position (B) and the rate (k) parameters, a reciprocal model was used to calculate the respective temperature functions. The nonlinear logistic model described successfully the response of appressorium formation to the combined effects of temperature and wetness period. Especially the temperature function for asymptote parameter A reflected the response of upper limit of appressorium formation to temperature, which showed the typical temperature response of enzymatic reactions in the cells. By having both temperature and wetness period as independent variables, the nonlinear logistic model can be used to determine the length of wetness periods required for certain levels of appressorium formation under different temperature conditions. The infection model derived from the nonlinear logistic model can be used to calculate infection risks using hourly temperature and wetness period data monitored by automated weather stations in the fields. Compared with the nonlinear infection model, the linear infection model always predicted a shorter wetness period for appressorium formation, and resulted in significantly under- and over-estimation of response at low and high temperatures, respectively.