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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

Ability of ABA mutants to infect rice. M-104 and Seraceltik rice plants were infected with 70-15, 70-15ΔABA4, or 70-15ΔGPCR and lesion length and width were measured. Photographs were taken 5 days after infection. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).
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Figure 7: Ability of ABA mutants to infect rice. M-104 and Seraceltik rice plants were infected with 70-15, 70-15ΔABA4, or 70-15ΔGPCR and lesion length and width were measured. Photographs were taken 5 days after infection. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).

Mentions: The mutants were also tested for their ability to form lesions on rice leaves. Strikingly, the 70-15ΔABA4 mutant was unable to properly infect. In many cases, the mutant did not have any effect on the leaf, or left a tiny black speck (Figure 7). The small spots that formed were much smaller than the lesions caused by 70-15 or 70-15ΔGPCR (Figure 7). When the experiment was extended for several more days, all of the leaves began drying and curling, and the lesions from 70-15 and 70-15ΔGPCR kept spreading, but the 70-15ΔABA4 spots did not grow. The mutants were also tested on plants that had been root-primed with EA105 for 24 h. EA105 retained the ability to reduce lesion size caused by 70-15 and 70-15ΔGPCR, but since 70-15ΔABA4 did not form lesions, there was no effect from EA105 priming. The same trend was apparent in rice cultivars M-104 and Seraceltik (Supplementary Figures S7–S9).


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)

Ability of ABA mutants to infect rice. M-104 and Seraceltik rice plants were infected with 70-15, 70-15ΔABA4, or 70-15ΔGPCR and lesion length and width were measured. Photographs were taken 5 days after infection. 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 7: Ability of ABA mutants to infect rice. M-104 and Seraceltik rice plants were infected with 70-15, 70-15ΔABA4, or 70-15ΔGPCR and lesion length and width were measured. Photographs were taken 5 days after infection. Different letters represent statistical significance based on the Tukey-Kramer test (p < 0.05).
Mentions: The mutants were also tested for their ability to form lesions on rice leaves. Strikingly, the 70-15ΔABA4 mutant was unable to properly infect. In many cases, the mutant did not have any effect on the leaf, or left a tiny black speck (Figure 7). The small spots that formed were much smaller than the lesions caused by 70-15 or 70-15ΔGPCR (Figure 7). When the experiment was extended for several more days, all of the leaves began drying and curling, and the lesions from 70-15 and 70-15ΔGPCR kept spreading, but the 70-15ΔABA4 spots did not grow. The mutants were also tested on plants that had been root-primed with EA105 for 24 h. EA105 retained the ability to reduce lesion size caused by 70-15 and 70-15ΔGPCR, but since 70-15ΔABA4 did not form lesions, there was no effect from EA105 priming. The same trend was apparent in rice cultivars M-104 and Seraceltik (Supplementary Figures S7–S9).

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