Acquired Resistance to Mefenoxam in Sensitive Isolates of Phytophthora infestans

The systemic fungicide mefenoxam has been important in the control of late blight disease caused by Phytophthora infestans. This phenylamide fungicide has a negative effect on the synthesis of ribosomal RNA; however, the genetic basis for inherited field resistance is still not completely clear. We recently observed that a sensitive isolate became tolerant after a single passage on mefenoxam-containing medium. Further analyses revealed that all sensitive isolates tested (in three diverse genotypes) acquired this resistance equally quickly. In contrast, isolates that were “resistant” to mefenoxam in the initial assessment (stably resistant) did not increase in resistance upon further exposure. However, there appeared to be a cost associated with acquired resistance in the initially sensitive isolates, in that isolates with acquired resistance grew more slowly on mefenoxam-free medium than did the same isolates that had never been exposed to mefenoxam. The acquired resistance of the sensitive isolates declined slightly with subsequent culturing on medium free of mefenoxam. To investigate the mechanism of acquired resistance, we employed strand-specific RNA sequencing. Many differentially expressed genes were genotype specific, but one set of genes was differentially expressed in all genotypes. Among these were several genes (a phospholipase “Pi-PLD-like-3,” two ATP-binding cassette superfamily [ABC] transporters, and a mannitol dehydrogenase) that were up-regulated and whose function might contribute to a resistance phenotype.

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Searching for the mechanism that mediates mefenoxam-acquired resistance in Phytophthora infestans and how it is regulated

Phytopathology ◽

10.1094/phyto-07-21-0280-r ◽

2021 ◽

Author(s):

Juliana González-Tobón ◽

Richard Childers ◽

Alejandra Rodríguez ◽

William Fry ◽

Kevin L. Myers ◽

...

Keyword(s):

Phytophthora Infestans ◽

Molecular Mechanisms ◽

Acquired Resistance ◽

Phytophthora Species ◽

Regulatory Process ◽

Differentially Expressed ◽

Potential Association ◽

Other Substances ◽

Blight Disease ◽

Computational Analyses

Phytophthora infestans, the causal agent of late blight disease of potatoes, is mainly controlled by the use of fungicides. Isolates that are resistant to commonly used fungicides have been reported. Also, several studies show that originally mefenoxam-sensitive isolates acquire resistance to this fungicide when exposed to sub-lethal concentrations. This phenomenon, termed ‘mefenoxam-acquired resistance’, has been observed in different Phytophthora species and seems to be unique to mefenoxam. In this study, we aimed to elucidate the molecular mechanism mediating this type of resistance as well as a possible regulatory process behind it. A combination of computational analyses and experimental approaches was used to identify differentially expressed genes with a potential association to the phenomenon. These genes were classified into seven functional groups. Most of them seem to be associated with a pleiotropic drug resistance (PDR) phenotype, typically involved in the expulsion of diverse metabolites, drugs, or other substances out of the cell. Despite the importance of RNApolI for the constitutive resistance of P. infestans to mefenoxam, our results indicate no clear interaction between this protein and the acquisition of mefenoxam resistance. Several small non-coding RNAs (ncRNAs) were found to be differentially expressed and specifically related to genes mediating the PDR phenotype, thus suggesting a possible regulatory process. We propose a model of the molecular mechanisms acting within the cell when P. infestans acquires resistance to mefenoxam after exposed to sub-lethal concentrations of the fungicide. This study provides important insights into P. infestans’ cellular and regulatory functionalities.

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Is the Phenomenon of Mefenoxam-Acquired Resistance in Phytophthora infestans Universal?

Plant Disease ◽

10.1094/pdis-10-18-1906-re ◽

2020 ◽

Vol 104 (1) ◽

pp. 211-221

Author(s):

Juliana González-Tobón ◽

Richard Childers ◽

Carolina Olave ◽

Melissa Regnier ◽

Alejandra Rodríguez-Jaramillo ◽

...

Keyword(s):

Phytophthora Infestans ◽

Acquired Resistance ◽

Phytophthora Species ◽

Economic Losses ◽

Phytophthora Spp ◽

Late Blight Disease ◽

Blight Disease ◽

And Control ◽

Sublethal Concentrations

Phytophthora infestans is the causal agent of late blight disease of potatoes and tomatoes. This disease causes devastating economic losses each year, and control is mainly achieved by the use of fungicides. Unfortunately, populations of P. infestans resistant to fungicides have been documented. Furthermore, studies have reported that sensitive isolates to the phenylamide fungicide, mefenoxam, become less sensitive in vitro after a single passage through sublethal concentrations of fungicide-amended medium. The first objective of this study was to investigate if isolates of P. infestans are capable of acquiring resistance to two additional systemic fungicides, fluopicolide (benzamide) and cymoxanil (cyanoacetamide-oxime). In contrast to the situation with mefenoxam, exposure of isolates to sublethal concentrations of fluopicolide and cymoxanil did not induce reduced sensitivity to these two fungicides. The second objective was to assess if reduced sensitivity to mefenoxam could occur in naturally sensitive isolates of other Phytophthora species and of Phytopythium sp., another oomycete plant pathogen. All Phytophthora spp. assessed (P. infestans, P. betacei, and P. pseudocryptogea) as well as Phytopythium sp. acquired resistance to mefenoxam after previous exposure through medium containing 1 µg ml−1 of mefenoxam. Interestingly, isolate 66 of Phytopythium sp. and the isolate of P. pseudocryptogea tested do not seem to be acquiring resistance to mefenoxam after exposure to medium containing 5 µg ml−1 of this fungicide. The tested isolates of P. palmivora and P. cinnamomi were extremely sensitive to mefenoxam, and thus it was not possible to perform a second transfer to access acquisition of resistance to this fungicide.

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Evaluation of bio-agents and neem based products against late blight disease (Phytophthora infestans) of potato

Indian Phytopathology ◽

10.1007/s42360-021-00330-6 ◽

2021 ◽

Vol 74 (1) ◽

pp. 181-187

Author(s):

Mehi Lal ◽

Sorabh Chaudhary ◽

Sanjay Rawal ◽

Sanjeev Sharma ◽

Manoj Kumar ◽

...

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Late Blight Disease ◽

Blight Disease

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Phenotypic Characterization of Recent Clonal Lineages of Phytophthora infestans in the United States

Plant Disease ◽

10.1094/pdis-07-12-0682-re ◽

2013 ◽

Vol 97 (7) ◽

pp. 873-881 ◽

Cited By ~ 48

Author(s):

G. Danies ◽

I. M. Small ◽

K. Myers ◽

R. Childers ◽

W. E. Fry

Keyword(s):

United States ◽

Late Blight ◽

Phytophthora Infestans ◽

The United States ◽

Phenotypic Characterization ◽

Phenotypic Traits ◽

Mating Types ◽

Late Blight Disease ◽

Blight Disease

Phytophthora infestans, the causal agent of late blight disease, has been reported in the United States and Canada since the mid-nineteenth century. Due to the lack of or very limited sexual reproduction, the populations of P. infestans in the United States are primarily reproducing asexually and, thus, show a simple genetic structure. The emergence of new clonal lineages of P. infestans (US-22, US-23, and US-24) responsible for the late blight epidemics in the northeastern region of the United States in the summers of 2009 and 2010 stimulated an investigation into phenotypic traits associated with these genotypes. Mating type, differences in sensitivity to mefenoxam, differences in pathogenicity on potato and tomato, and differences in rate of germination were studied for clonal lineages US-8, US-22, US-23, and US-24. Both A1 and A2 mating types were detected. Lineages US-22, US-23, and US-24 were generally sensitive to mefenoxam while US-8 was resistant. US-8 and US-24 were primarily pathogenic on potato while US-22 and US-23 were pathogenic on both potato and tomato. Indirect germination was favored at lower temperatures (5 and 10°C) whereas direct germination, though uncommon, was favored at higher temperatures (20 and 25°C). Sporangia of US-24 released zoospores more rapidly than did sporangia of US-22 and US-23. The association of characteristic phenotypic traits with genotype enables the prediction of phenotypic traits from rapid genotypic analyses for improved disease management.

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Phytophthora infestans Sporangia Produced in Culture and on Tomato Leaflet Lesions Show Marked Differences in Indirect Germination Rates, Aggressiveness, and Global Transcription Profiles

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-09-18-0255-ta ◽

2019 ◽

Vol 32 (5) ◽

pp. 515-526 ◽

Cited By ~ 5

Author(s):

William E. Fry ◽

Sean P. Patev ◽

Kevin L. Myers ◽

Kan Bao ◽

Zhangjun Fei

Keyword(s):

Phytophthora Infestans ◽

Differentially Expressed Genes ◽

Differentially Expressed ◽

Rna Seq ◽

Moist Chamber ◽

Field Isolates ◽

Rxlr Effectors ◽

Transcription Profiles ◽

Independent Field ◽

Pure Cultures

Sporangia of Phytophthora infestans from pure cultures on agar plates are typically used in lab studies, whereas sporangia from leaflet lesions drive natural infections and epidemics. Multiple assays were performed to determine if sporangia from these two sources are equivalent. Sporangia from plate cultures showed much lower rates of indirect germination and produced much less disease in field and moist-chamber tests. This difference in aggressiveness was observed whether the sporangia had been previously incubated at 4°C (to induce indirect germination) or at 21°C (to prevent indirect germination). Furthermore, lesions caused by sporangia from plates produced much less sporulation. RNA-Seq analysis revealed that thousands of the >17,000 P. infestans genes with a RPKM (reads per kilobase of exon model per million mapped reads) >1 were differentially expressed in sporangia obtained from plate cultures of two independent field isolates compared with sporangia of those isolates from leaflet lesions. Among the significant differentially expressed genes (DEGs), putative RxLR effectors were overrepresented, with almost half of the 355 effectors with RPKM >1 being up- or downregulated. DEGs of both isolates include nine flagellar-associated genes, and all were down-regulated in plate sporangia. Ten elicitin genes were also detected as DEGs in both isolates, and nine (including INF1) were up-regulated in plate sporangia. These results corroborate previous observations that sporangia produced from plates and leaflets sometimes yield different experimental results and suggest hypotheses for potential mechanisms. We caution that use of plate sporangia in assays may not always produce results reflective of natural infections and epidemics.

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The nature and inheritance of field resistance to late blight (Phytophthora infestans) in potatoes

American Potato Journal ◽

10.1007/bf02863003 ◽

1970 ◽

Vol 47 (8) ◽

pp. 279-288 ◽

Cited By ~ 47

Author(s):

W. Black

Keyword(s):

Late Blight ◽

Phytophthora Infestans ◽

Field Resistance

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Transcriptome analysis of Phytophthora infestans and Colletotrichum coccodes in tomato to reveal resistance mechanisms

Asia Pacific Journal of Molecular Biology and Biotechnology ◽

10.35118/apjmbb.2020.028.1.05 ◽

2020 ◽

pp. 39-51

Author(s):

Abbas Saidi ◽

Zahra Hajibarat ◽

Zohreh Hajibarat

Keyword(s):

Phytophthora Infestans ◽

Expression Analysis ◽

Organic Substance ◽

Regulatory Elements ◽

Differentially Expressed ◽

Tata Box ◽

Colletotrichum Coccodes ◽

Growth Stages ◽

Cis Elements ◽

Study Gene Expression

Tomato is considered as an important commercial crop and protective food and it’s yield is extremely affected by different pathogens. Such harmful pathogens severely affecting tomato include Phytophthora infestans (oomycete) and Colletotrichum coccodes (fungi). In this study, gene expression analysis was performed using the microarray datasets available in the public database to investigate differentially expressed genes DEGs under developmental and anatomy conditions and consequently constructing the predicted PPI (Protein-protein interaction) network. Here, a comparison of abundances revealed that 51 genes were differentially expressed due to oomycete and fungi stresses in tomato. Expression analysis revealed that Solyc06g007510.3 was up-regulated whereas Solyc05g008850.3 was down-regulated in all developmental stages and anatomy conditions to manage auxin metabolism under fungi and oomycete infections in tomato. The gene ontology included cellular metabolic and organic substance metabolic processes, cellular biosynthetic, organic substance biosynthetic, and cellular macromolecule metabolic process, chloroplast, intracellular membrane-bounded organelle, heterocyclic compound binding, organic cyclic compound binding, ion binding, binding, and catalytic activity. Analysis of cis-elements illustrated that 12 most general cis-regulatory elements (CATT-box, TATA-box, MYB, MYC, ABRE, G-box, Box 4, AAGAA-motif, MBS, as-1, TGACG-motif, and CGTCA-motif) were identified in promoter region. The highest frequency of cis-elements included CATT-box and TATA-box in response to the pathogens at different growth stages in tomato. Our findings can provide a better insight to the regulatory mechanisms involved in response to fungi and oomycete infection in tomato which can aid to improve the efficiency of developing tomato varieties.

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