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Crucial Roles of Abscisic Acid Biogenesis in Virulence of Rice Blast Fungus Magnaporthe oryzae.

Spence CA, Lakshmanan V, Donofrio N, Bais HP - Front Plant Sci (2015)

Bottom Line: EA105 may be reducing the virulence of M. oryzae by preventing the pathogen from up-regulating the key ABA biosynthetic gene NCED3 in rice roots, as well as a β-glucosidase likely involved in activating conjugated inactive forms of ABA.EA105, which inhibits appressoria formation, counteracted the virulence-promoting effects of ABA on M. oryzae.ABA is a molecule that is likely implicated in both tactics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Delaware Newark, DE, USA ; Delaware Biotechnology Institute Newark, DE, USA ; Department of Plant and Soil Sciences, University of Delaware Newark, DE, USA.

ABSTRACT
Rice suffers dramatic yield losses due to blast pathogen Magnaporthe oryzae. Pseudomonas chlororaphis EA105, a bacterium that was isolated from the rice rhizosphere, inhibits M. oryzae. It was shown previously that pre-treatment of rice with EA105 reduced the size of blast lesions through jasmonic acid (JA)- and ethylene (ETH)-mediated ISR. Abscisic acid (ABA) acts antagonistically toward salicylic acid (SA), JA, and ETH signaling, to impede plant defense responses. EA105 may be reducing the virulence of M. oryzae by preventing the pathogen from up-regulating the key ABA biosynthetic gene NCED3 in rice roots, as well as a β-glucosidase likely involved in activating conjugated inactive forms of ABA. However, changes in total ABA concentrations were not apparent, provoking the question of whether ABA concentration is an indicator of ABA signaling and response. In the rice-M. oryzae interaction, ABA plays a dual role in disease severity by increasing plant susceptibility and accelerating pathogenesis in the fungus itself. ABA is biosynthesized by M. oryzae. Further, exogenous ABA increased spore germination and appressoria formation, distinct from other plant growth regulators. EA105, which inhibits appressoria formation, counteracted the virulence-promoting effects of ABA on M. oryzae. The role of endogenous fungal ABA in blast disease was confirmed through the inability of a knockout mutant impaired in ABA biosynthesis to form lesions on rice. Therefore, it appears that EA105 is invoking multiple strategies in its protection of rice from blast including direct mechanisms as well as those mediated through plant signaling. ABA is a molecule that is likely implicated in both tactics.

No MeSH data available.


Related in: MedlinePlus

Spore germination and appressoria formation in 70-15 and ABA mutants. (A) Spore germination was measured 3 h after resuspension and incubation on a hydrophobic plastic coverslip. (B) Appressoria formation was measured at 24 h. (C) Light microscope images were taken in areas which were dense with spores (top row) as well as in sparse areas where individual spores could be discerned. An enlarged imaged of the ABA4 mutant is displayed to show the hyperbranching phenotype. Scale bars are 50 μM. Supplementation of ABA (100 μM) reverts the phenotype in ABA4 mutant. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).
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Figure 6: Spore germination and appressoria formation in 70-15 and ABA mutants. (A) Spore germination was measured 3 h after resuspension and incubation on a hydrophobic plastic coverslip. (B) Appressoria formation was measured at 24 h. (C) Light microscope images were taken in areas which were dense with spores (top row) as well as in sparse areas where individual spores could be discerned. An enlarged imaged of the ABA4 mutant is displayed to show the hyperbranching phenotype. Scale bars are 50 μM. Supplementation of ABA (100 μM) reverts the phenotype in ABA4 mutant. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).

Mentions: An attempt was made to knock out ABA1, 2, and 4 in 70-15, however, potential ABA1 and ABA2 mutants were extremely slow growing and small, and we were unable to confirm that these were mutants. ABA4 was successfully knocked out, as well as the ABA GPCR (Supplementary Figure S5). The GPCR mutant largely resembled the parental 70-15, but the ABA4 mutant had distinct phenotypic differences in multiple stages of its life cycle. Vegetatively, the 70-15ΔABA4 mutant grew slower than 70-15 and never reached the same size (Figure 5A). Additionally, the mycelia became darkly pigmented beginning around 7 days after re-culturing and striking difference were apparent by 14 days (Figure 5B). Sporulation was also impaired in 70-15ΔABA4, while 70-15ΔGPCR produced more conidia than 70-15 (Supplementary Figure S7). The appearance of the 70-15ΔABA4 spores was also different than that of the wild-type, with unusual white patches visible on the spore plates (Supplementary Figure S7). Additionally, a very dark pigment was secreted into the media, and was left behind after spores were removed from the plates. There were not any significant differences in germination, although germination of both mutants was inhibited by EA105 treatment, which was not the case for 70-15 (Figure 6A). The 70-15ΔABA4 mutant was severely impaired in appressoria formation as compared to the other two strains (Figure 6B) and there were distinct phenotypic differences that could be seen microscopically. The ABA4 mutants showed hyper-branching of the germ tubes, as well as unusual bulges along the hyphae with less melainized appressoria (Figure 6C).


Crucial Roles of Abscisic Acid Biogenesis in Virulence of Rice Blast Fungus Magnaporthe oryzae.

Spence CA, Lakshmanan V, Donofrio N, Bais HP - Front Plant Sci (2015)

Spore germination and appressoria formation in 70-15 and ABA mutants. (A) Spore germination was measured 3 h after resuspension and incubation on a hydrophobic plastic coverslip. (B) Appressoria formation was measured at 24 h. (C) Light microscope images were taken in areas which were dense with spores (top row) as well as in sparse areas where individual spores could be discerned. An enlarged imaged of the ABA4 mutant is displayed to show the hyperbranching phenotype. Scale bars are 50 μM. Supplementation of ABA (100 μM) reverts the phenotype in ABA4 mutant. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664623&req=5

Figure 6: Spore germination and appressoria formation in 70-15 and ABA mutants. (A) Spore germination was measured 3 h after resuspension and incubation on a hydrophobic plastic coverslip. (B) Appressoria formation was measured at 24 h. (C) Light microscope images were taken in areas which were dense with spores (top row) as well as in sparse areas where individual spores could be discerned. An enlarged imaged of the ABA4 mutant is displayed to show the hyperbranching phenotype. Scale bars are 50 μM. Supplementation of ABA (100 μM) reverts the phenotype in ABA4 mutant. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).
Mentions: An attempt was made to knock out ABA1, 2, and 4 in 70-15, however, potential ABA1 and ABA2 mutants were extremely slow growing and small, and we were unable to confirm that these were mutants. ABA4 was successfully knocked out, as well as the ABA GPCR (Supplementary Figure S5). The GPCR mutant largely resembled the parental 70-15, but the ABA4 mutant had distinct phenotypic differences in multiple stages of its life cycle. Vegetatively, the 70-15ΔABA4 mutant grew slower than 70-15 and never reached the same size (Figure 5A). Additionally, the mycelia became darkly pigmented beginning around 7 days after re-culturing and striking difference were apparent by 14 days (Figure 5B). Sporulation was also impaired in 70-15ΔABA4, while 70-15ΔGPCR produced more conidia than 70-15 (Supplementary Figure S7). The appearance of the 70-15ΔABA4 spores was also different than that of the wild-type, with unusual white patches visible on the spore plates (Supplementary Figure S7). Additionally, a very dark pigment was secreted into the media, and was left behind after spores were removed from the plates. There were not any significant differences in germination, although germination of both mutants was inhibited by EA105 treatment, which was not the case for 70-15 (Figure 6A). The 70-15ΔABA4 mutant was severely impaired in appressoria formation as compared to the other two strains (Figure 6B) and there were distinct phenotypic differences that could be seen microscopically. The ABA4 mutants showed hyper-branching of the germ tubes, as well as unusual bulges along the hyphae with less melainized appressoria (Figure 6C).

Bottom Line: EA105 may be reducing the virulence of M. oryzae by preventing the pathogen from up-regulating the key ABA biosynthetic gene NCED3 in rice roots, as well as a β-glucosidase likely involved in activating conjugated inactive forms of ABA.EA105, which inhibits appressoria formation, counteracted the virulence-promoting effects of ABA on M. oryzae.ABA is a molecule that is likely implicated in both tactics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Delaware Newark, DE, USA ; Delaware Biotechnology Institute Newark, DE, USA ; Department of Plant and Soil Sciences, University of Delaware Newark, DE, USA.

ABSTRACT
Rice suffers dramatic yield losses due to blast pathogen Magnaporthe oryzae. Pseudomonas chlororaphis EA105, a bacterium that was isolated from the rice rhizosphere, inhibits M. oryzae. It was shown previously that pre-treatment of rice with EA105 reduced the size of blast lesions through jasmonic acid (JA)- and ethylene (ETH)-mediated ISR. Abscisic acid (ABA) acts antagonistically toward salicylic acid (SA), JA, and ETH signaling, to impede plant defense responses. EA105 may be reducing the virulence of M. oryzae by preventing the pathogen from up-regulating the key ABA biosynthetic gene NCED3 in rice roots, as well as a β-glucosidase likely involved in activating conjugated inactive forms of ABA. However, changes in total ABA concentrations were not apparent, provoking the question of whether ABA concentration is an indicator of ABA signaling and response. In the rice-M. oryzae interaction, ABA plays a dual role in disease severity by increasing plant susceptibility and accelerating pathogenesis in the fungus itself. ABA is biosynthesized by M. oryzae. Further, exogenous ABA increased spore germination and appressoria formation, distinct from other plant growth regulators. EA105, which inhibits appressoria formation, counteracted the virulence-promoting effects of ABA on M. oryzae. The role of endogenous fungal ABA in blast disease was confirmed through the inability of a knockout mutant impaired in ABA biosynthesis to form lesions on rice. Therefore, it appears that EA105 is invoking multiple strategies in its protection of rice from blast including direct mechanisms as well as those mediated through plant signaling. ABA is a molecule that is likely implicated in both tactics.

No MeSH data available.


Related in: MedlinePlus