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Bacterial endophytes from wild maize suppress Fusarium graminearum in modern maize and inhibit mycotoxin accumulation.

Mousa WK, Shearer CR, Limay-Rios V, Zhou T, Raizada MN - Front Plant Sci (2015)

Bottom Line: The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels.Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture.We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Agriculture, University of Guelph Guelph, ON, Canada ; Department of Pharmacognosy, Mansoura University Mansoura, Egypt.

ABSTRACT
Wild maize (teosinte) has been reported to be less susceptible to pests than their modern maize (corn) relatives. Endophytes, defined as microbes that inhabit plants without causing disease, are known for their ability to antagonize plant pests and pathogens. We hypothesized that the wild relatives of modern maize may host endophytes that combat pathogens. Fusarium graminearum is the fungus that causes Gibberella Ear Rot (GER) in modern maize and produces the mycotoxin, deoxynivalenol (DON). In this study, 215 bacterial endophytes, previously isolated from diverse maize genotypes including wild teosintes, traditional landraces and modern varieties, were tested for their ability to antagonize F. graminearum in vitro. Candidate endophytes were then tested for their ability to suppress GER in modern maize in independent greenhouse trials. The results revealed that three candidate endophytes derived from wild teosintes were most potent in suppressing F. graminearum in vitro and GER in a modern maize hybrid. These wild teosinte endophytes could suppress a broad spectrum of fungal pathogens of modern crops in vitro. The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels. A fourth, less robust anti-fungal strain was isolated from a modern maize hybrid. Three of the anti-fungal endophytes were predicted to be Paenibacillus polymyxa, along with one strain of Citrobacter. Microscopy studies suggested a fungicidal mode of action by all four strains. Molecular and biochemical studies showed that the P. polymyxa strains produced the previously characterized anti-Fusarium compound, fusaricidin. Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture. We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

No MeSH data available.


Related in: MedlinePlus

Molecular and biochemical detection of the candidate anti-fungal compound, fusaricidin, in Paenibacillus strains. (A) Details of fusA gene orthologs isolated from the candidate Paenibacillus endophytes by PCR amplification. (B–D) Combined ion chromatogram/mass spectrum for candidate fusaricidin derivatives detected in the cultures of the Penibacillus endophytes as indicated.
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Figure 6: Molecular and biochemical detection of the candidate anti-fungal compound, fusaricidin, in Paenibacillus strains. (A) Details of fusA gene orthologs isolated from the candidate Paenibacillus endophytes by PCR amplification. (B–D) Combined ion chromatogram/mass spectrum for candidate fusaricidin derivatives detected in the cultures of the Penibacillus endophytes as indicated.

Mentions: A candidate gene approach was undertaken to help understand the fungicide mode of action of the endophytes. Paenibacillus are well known to produce fusaricidin compounds that combat various fungal pathogens including F. graminearum; the compound is in fact named after Fusarium (Kajimura and Kaneda, 1996, 1997; Beatty and Jensen, 2002; Choi et al., 2008). To detect the presence of fusaricidin biosynthetic genes in the three predicted Paenibacillus strains, PCR primers were designed based on the fusaricidin synthase gene sequence (GenBank accession # EU184010). Each genome amplified a single band that was sequenced; the results revealed that all three of the Paenibacillus endophyte genomes encode a putative fusA ortholog, with DNA sequence identities ranging from 92 to 94% (Figure 6A, Table S2). GenBank accession numbers for fusA sequences amplified from strains 1D6, 3H9, 4G4 were KT343965, KT343966, and KT343967, respectively. FusA is a non-ribosomal peptide synthetase with relaxed substrate specificity that can incorporate different amino acids, resulting in different fusaricidin derivatives (Han et al., 2012). To confirm that the fusA orthologs were expressed by the endophytes, and to identify the specific fusaricidin derivatives produced, LC/MS was employed. Peaks with M + Z similar to fusaricidin C (947.6), fusaricidin B (883), and fusaricidin D (961.7) were detected in the liquid cultures of strains 1D6, 3H9, and 4G4, respectively (Figures 6B–D) (Kajimura and Kaneda, 1996, 1997; Beatty and Jensen, 2002). Combined, these results demonstrate that the well-known anti-Fusarium compound fusaricidin is encoded and expressed by each of the three Paenibacillus endophytes.


Bacterial endophytes from wild maize suppress Fusarium graminearum in modern maize and inhibit mycotoxin accumulation.

Mousa WK, Shearer CR, Limay-Rios V, Zhou T, Raizada MN - Front Plant Sci (2015)

Molecular and biochemical detection of the candidate anti-fungal compound, fusaricidin, in Paenibacillus strains. (A) Details of fusA gene orthologs isolated from the candidate Paenibacillus endophytes by PCR amplification. (B–D) Combined ion chromatogram/mass spectrum for candidate fusaricidin derivatives detected in the cultures of the Penibacillus endophytes as indicated.
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Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4593954&req=5

Figure 6: Molecular and biochemical detection of the candidate anti-fungal compound, fusaricidin, in Paenibacillus strains. (A) Details of fusA gene orthologs isolated from the candidate Paenibacillus endophytes by PCR amplification. (B–D) Combined ion chromatogram/mass spectrum for candidate fusaricidin derivatives detected in the cultures of the Penibacillus endophytes as indicated.
Mentions: A candidate gene approach was undertaken to help understand the fungicide mode of action of the endophytes. Paenibacillus are well known to produce fusaricidin compounds that combat various fungal pathogens including F. graminearum; the compound is in fact named after Fusarium (Kajimura and Kaneda, 1996, 1997; Beatty and Jensen, 2002; Choi et al., 2008). To detect the presence of fusaricidin biosynthetic genes in the three predicted Paenibacillus strains, PCR primers were designed based on the fusaricidin synthase gene sequence (GenBank accession # EU184010). Each genome amplified a single band that was sequenced; the results revealed that all three of the Paenibacillus endophyte genomes encode a putative fusA ortholog, with DNA sequence identities ranging from 92 to 94% (Figure 6A, Table S2). GenBank accession numbers for fusA sequences amplified from strains 1D6, 3H9, 4G4 were KT343965, KT343966, and KT343967, respectively. FusA is a non-ribosomal peptide synthetase with relaxed substrate specificity that can incorporate different amino acids, resulting in different fusaricidin derivatives (Han et al., 2012). To confirm that the fusA orthologs were expressed by the endophytes, and to identify the specific fusaricidin derivatives produced, LC/MS was employed. Peaks with M + Z similar to fusaricidin C (947.6), fusaricidin B (883), and fusaricidin D (961.7) were detected in the liquid cultures of strains 1D6, 3H9, and 4G4, respectively (Figures 6B–D) (Kajimura and Kaneda, 1996, 1997; Beatty and Jensen, 2002). Combined, these results demonstrate that the well-known anti-Fusarium compound fusaricidin is encoded and expressed by each of the three Paenibacillus endophytes.

Bottom Line: The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels.Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture.We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Agriculture, University of Guelph Guelph, ON, Canada ; Department of Pharmacognosy, Mansoura University Mansoura, Egypt.

ABSTRACT
Wild maize (teosinte) has been reported to be less susceptible to pests than their modern maize (corn) relatives. Endophytes, defined as microbes that inhabit plants without causing disease, are known for their ability to antagonize plant pests and pathogens. We hypothesized that the wild relatives of modern maize may host endophytes that combat pathogens. Fusarium graminearum is the fungus that causes Gibberella Ear Rot (GER) in modern maize and produces the mycotoxin, deoxynivalenol (DON). In this study, 215 bacterial endophytes, previously isolated from diverse maize genotypes including wild teosintes, traditional landraces and modern varieties, were tested for their ability to antagonize F. graminearum in vitro. Candidate endophytes were then tested for their ability to suppress GER in modern maize in independent greenhouse trials. The results revealed that three candidate endophytes derived from wild teosintes were most potent in suppressing F. graminearum in vitro and GER in a modern maize hybrid. These wild teosinte endophytes could suppress a broad spectrum of fungal pathogens of modern crops in vitro. The teosinte endophytes also suppressed DON mycotoxin during storage to below acceptable safety threshold levels. A fourth, less robust anti-fungal strain was isolated from a modern maize hybrid. Three of the anti-fungal endophytes were predicted to be Paenibacillus polymyxa, along with one strain of Citrobacter. Microscopy studies suggested a fungicidal mode of action by all four strains. Molecular and biochemical studies showed that the P. polymyxa strains produced the previously characterized anti-Fusarium compound, fusaricidin. Our results suggest that the wild relatives of modern crops may serve as a valuable reservoir for endophytes in the ongoing fight against serious threats to modern agriculture. We discuss the possible impact of crop evolution and domestication on endophytes in the context of plant defense.

No MeSH data available.


Related in: MedlinePlus