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Microbial pathogens trigger host DNA double-strand breaks whose abundance is reduced by plant defense responses.

Song J, Bent AF - PLoS Pathog. (2014)

Bottom Line: Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs.However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF.The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Pathology, University of Wisconsin - Madison, Madison, Wisconsin, United States of America.

ABSTRACT
Immune responses and DNA damage repair are two fundamental processes that have been characterized extensively, but the links between them remain largely unknown. We report that multiple bacterial, fungal and oomycete plant pathogen species induce double-strand breaks (DSBs) in host plant DNA. DNA damage detected by histone γ-H2AX abundance or DNA comet assays arose hours before the disease-associated necrosis caused by virulent Pseudomonas syringae pv. tomato. Necrosis-inducing paraquat did not cause detectable DSBs at similar stages after application. Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs. Elevation of reactive oxygen species (ROS) is common during plant immune responses, ROS are known DNA damaging agents, and the infection-induced host ROS burst has been implicated as a cause of host DNA damage in animal studies. However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF. Plant MAMP receptor stimulation or application of defense-activating salicylic acid or jasmonic acid failed to induce a detectable level of DSBs in the absence of introduced pathogens, further suggesting that pathogen activities beyond host defense activation cause infection-induced DNA damage. The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses. Infection-induced formation of γ-H2AX still occurred in Arabidopsis atr/atm double mutants, suggesting the presence of an alternative mediator of pathogen-induced H2AX phosphorylation. In summary, pathogenic microorganisms can induce plant DNA damage. Plant defense mechanisms help to suppress rather than promote this damage, thereby contributing to the maintenance of genome integrity in somatic tissues.

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Pst-induced γ-H2AX accumulation is independent of Pst-triggered ROS production.Four-week old wild-type Arabidopsis Col, atrbohD and atrbohDF plants were vacuum-infiltrated with (A) Pst DC3000 or (B) Pst DC3000(avrRpt2) at a concentration of 1×107 cfu/ml. The level of γ-H2AX was assessed at 2, 4 and 8 h postinoculation by immunoblot using anti-γ-H2AX antibody. Equivalent loading of lanes was verified using Ponceau S stain.
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ppat-1004030-g004: Pst-induced γ-H2AX accumulation is independent of Pst-triggered ROS production.Four-week old wild-type Arabidopsis Col, atrbohD and atrbohDF plants were vacuum-infiltrated with (A) Pst DC3000 or (B) Pst DC3000(avrRpt2) at a concentration of 1×107 cfu/ml. The level of γ-H2AX was assessed at 2, 4 and 8 h postinoculation by immunoblot using anti-γ-H2AX antibody. Equivalent loading of lanes was verified using Ponceau S stain.

Mentions: Elevated ROS are a primary feature of plant defense responses and a possible source of the host DNA damage associated with pathogen infections [3], [17], [18], [61], [62]. Virulent P. syringae elicit a rapid but transient accumulation of ROS in plants over approximately the first half hour after infection, while P. syringae expressing a recognized avirulence gene induce the first wave as well as a second wave of elevated ROS that is more massive and prolonged [16]. However, ROS production induced by bacterial and oomycete pathogens is nearly eliminated in Arabidopsis atrbohD single and atrbohDF double mutants with disruptions in the corresponding NADPH oxidase catalytic subunits [17], [63]. We examined the γ-H2AX level in response to pathogen infections in the atrbohD and atrbohDF mutant plants. There was no obvious reduction of γ-H2AX (Figure 4), in response to either virulent Pst DC3000 or avirulent Pst DC3000(avrRpt2), indicating that pathogen-triggered NADPH-derived ROS production is not the primary cause or a required component of the formation of pathogen-induced DSBs.


Microbial pathogens trigger host DNA double-strand breaks whose abundance is reduced by plant defense responses.

Song J, Bent AF - PLoS Pathog. (2014)

Pst-induced γ-H2AX accumulation is independent of Pst-triggered ROS production.Four-week old wild-type Arabidopsis Col, atrbohD and atrbohDF plants were vacuum-infiltrated with (A) Pst DC3000 or (B) Pst DC3000(avrRpt2) at a concentration of 1×107 cfu/ml. The level of γ-H2AX was assessed at 2, 4 and 8 h postinoculation by immunoblot using anti-γ-H2AX antibody. Equivalent loading of lanes was verified using Ponceau S stain.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974866&req=5

ppat-1004030-g004: Pst-induced γ-H2AX accumulation is independent of Pst-triggered ROS production.Four-week old wild-type Arabidopsis Col, atrbohD and atrbohDF plants were vacuum-infiltrated with (A) Pst DC3000 or (B) Pst DC3000(avrRpt2) at a concentration of 1×107 cfu/ml. The level of γ-H2AX was assessed at 2, 4 and 8 h postinoculation by immunoblot using anti-γ-H2AX antibody. Equivalent loading of lanes was verified using Ponceau S stain.
Mentions: Elevated ROS are a primary feature of plant defense responses and a possible source of the host DNA damage associated with pathogen infections [3], [17], [18], [61], [62]. Virulent P. syringae elicit a rapid but transient accumulation of ROS in plants over approximately the first half hour after infection, while P. syringae expressing a recognized avirulence gene induce the first wave as well as a second wave of elevated ROS that is more massive and prolonged [16]. However, ROS production induced by bacterial and oomycete pathogens is nearly eliminated in Arabidopsis atrbohD single and atrbohDF double mutants with disruptions in the corresponding NADPH oxidase catalytic subunits [17], [63]. We examined the γ-H2AX level in response to pathogen infections in the atrbohD and atrbohDF mutant plants. There was no obvious reduction of γ-H2AX (Figure 4), in response to either virulent Pst DC3000 or avirulent Pst DC3000(avrRpt2), indicating that pathogen-triggered NADPH-derived ROS production is not the primary cause or a required component of the formation of pathogen-induced DSBs.

Bottom Line: Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs.However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF.The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Pathology, University of Wisconsin - Madison, Madison, Wisconsin, United States of America.

ABSTRACT
Immune responses and DNA damage repair are two fundamental processes that have been characterized extensively, but the links between them remain largely unknown. We report that multiple bacterial, fungal and oomycete plant pathogen species induce double-strand breaks (DSBs) in host plant DNA. DNA damage detected by histone γ-H2AX abundance or DNA comet assays arose hours before the disease-associated necrosis caused by virulent Pseudomonas syringae pv. tomato. Necrosis-inducing paraquat did not cause detectable DSBs at similar stages after application. Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs. Elevation of reactive oxygen species (ROS) is common during plant immune responses, ROS are known DNA damaging agents, and the infection-induced host ROS burst has been implicated as a cause of host DNA damage in animal studies. However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF. Plant MAMP receptor stimulation or application of defense-activating salicylic acid or jasmonic acid failed to induce a detectable level of DSBs in the absence of introduced pathogens, further suggesting that pathogen activities beyond host defense activation cause infection-induced DNA damage. The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses. Infection-induced formation of γ-H2AX still occurred in Arabidopsis atr/atm double mutants, suggesting the presence of an alternative mediator of pathogen-induced H2AX phosphorylation. In summary, pathogenic microorganisms can induce plant DNA damage. Plant defense mechanisms help to suppress rather than promote this damage, thereby contributing to the maintenance of genome integrity in somatic tissues.

Show MeSH
Related in: MedlinePlus