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Phytohormone-mediated interkingdom signaling shapes the outcome of rice-Xanthomonas oryzae pv. oryzae interactions.

Xu J, Zhou L, Venturi V, He YW, Kojima M, Sakakibari H, Höfte M, De Vleesschauwer D - BMC Plant Biol. (2015)

Bottom Line: Employing the rice-Xanthomonas oryzae pv. oryzae (Xoo) interaction as a model system, we show that Xoo uses the classic immune hormone salicylic acid (SA) as a trigger to activate its virulence-associated quorum sensing (QS) machinery.Despite repressing swimming motility, sodium salicylate (NaSA) induced production of the Diffusible Signal Factor (DSF) and Diffusible Factor (DF) QS signals, with resultant accumulation of xanthomonadin and extracellular polysaccharides.Moreover, we found both DF and DSF to influence SA- and ABA-responsive gene expression in planta.

View Article: PubMed Central - PubMed

Affiliation: Lab of Phytopathology, Department of Crop Protection, Ghent University, Coupure Links 653, 9000, Ghent, Belgium. jing.xu@ugent.be.

ABSTRACT

Background: Small-molecule hormones are well known to play key roles in the plant immune signaling network that is activated upon pathogen perception. In contrast, little is known about whether phytohormones also directly influence microbial virulence, similar to what has been reported in animal systems.

Results: In this paper, we tested the hypothesis that hormones fulfill dual roles in plant-microbe interactions by orchestrating host immune responses, on the one hand, and modulating microbial virulence traits, on the other. Employing the rice-Xanthomonas oryzae pv. oryzae (Xoo) interaction as a model system, we show that Xoo uses the classic immune hormone salicylic acid (SA) as a trigger to activate its virulence-associated quorum sensing (QS) machinery. Despite repressing swimming motility, sodium salicylate (NaSA) induced production of the Diffusible Signal Factor (DSF) and Diffusible Factor (DF) QS signals, with resultant accumulation of xanthomonadin and extracellular polysaccharides. In contrast, abscisic acid (ABA), which favors infection by Xoo, had little impact on DF- and DSF-mediated QS, but promoted bacterial swimming via the LuxR solo protein OryR. Moreover, we found both DF and DSF to influence SA- and ABA-responsive gene expression in planta.

Conclusions: Together our findings indicate that the rice SA and ABA signaling pathways cross-communicate with the Xoo DF and DSF QS systems and underscore the importance of bidirectional interkingdom signaling in molding plant-microbe interactions.

No MeSH data available.


Related in: MedlinePlus

NaSA suppresses basal and DSF-induced swimming motility ofXanthomonas oryzaepv.oryzae(Xoo) strain XKK12 (pPIP122). (A) and (B) Various concentrations of NaSA were added to swimming plates prior to inoculation with 3 μl XKK12 WT (pPIP122) suspension (109 CFU/ml). The plates were incubated for four days at 25°C and evaluated by measuring the diameter of the swimming zone. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05). (C), Phenotype of XKK12 WT (pPIP122) on swimming plates containing 0 (left) or 1 mM NaSA (right). (D), Effects of 1 mM NaSA, 2 mM NaSA and/or 3 μM DSF on the swimming of XKK12 WT (pPIP122) and oryR knockout mutant (pPIP122) (oryR−) bacteria. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05).
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Fig1: NaSA suppresses basal and DSF-induced swimming motility ofXanthomonas oryzaepv.oryzae(Xoo) strain XKK12 (pPIP122). (A) and (B) Various concentrations of NaSA were added to swimming plates prior to inoculation with 3 μl XKK12 WT (pPIP122) suspension (109 CFU/ml). The plates were incubated for four days at 25°C and evaluated by measuring the diameter of the swimming zone. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05). (C), Phenotype of XKK12 WT (pPIP122) on swimming plates containing 0 (left) or 1 mM NaSA (right). (D), Effects of 1 mM NaSA, 2 mM NaSA and/or 3 μM DSF on the swimming of XKK12 WT (pPIP122) and oryR knockout mutant (pPIP122) (oryR−) bacteria. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05).

Mentions: Mounting evidence indicates that SA is an important player in the activation of rice defenses against Xoo [36,38]. In a first attempt to test whether SA also exerts direct effects on the QS machinery of Xoo, we evaluated the effect of SA on the swimming ability of Xoo strain XKK12 (pPIP122). Unless specified otherwise, this strain was routinely used throughout this paper. Since SA showed strong inhibition of bacterial growth in both liquid and solid medium in our preliminary trials, all following experiments were performed using sodium salicylate (NaSA), which had no significant impact on XKK12 growth rates on (semi-)solid agar plates (data not shown). Swim plates indicated that XKK12 is motile in swimming medium, reaching a diameter of about 20 mm after 4-6 days of incubation at 25°C. As shown in Figures 1A to 1C, NaSA at concentrations of 20 μM, 0.1 mM and 0.5 mM had little or no significant effect on the swimming ability of XKK12, whereas 1 mM and 2 mM of NaSA significantly reduced swimming. SA concentrations in basal rice leaves range from 5 to 20 μg/g fresh weight [39]. To shed light on the SA concentrations in pathogen-inoculated rice leaves, we used a previously published UPLC-MS/MS method to profile the hormone signature of Xoo-infected rice plants at various times post inoculation [40]. Consistent with previous reports, SA levels remained fairly constant throughout the course of infection, except for a late two-fold increase at 8 dpi (Additional file 1). At this time point, SA levels reached 613235 ± 12043 pmol/g FW, which corresponds to 0.767 mM SA. Supplying bacteria with 1 or 2 mM NaSA thus resembles the amount of SA encountered by Xoo in planta, demonstrating the physiological relevance of these concentrations.Figure 1


Phytohormone-mediated interkingdom signaling shapes the outcome of rice-Xanthomonas oryzae pv. oryzae interactions.

Xu J, Zhou L, Venturi V, He YW, Kojima M, Sakakibari H, Höfte M, De Vleesschauwer D - BMC Plant Biol. (2015)

NaSA suppresses basal and DSF-induced swimming motility ofXanthomonas oryzaepv.oryzae(Xoo) strain XKK12 (pPIP122). (A) and (B) Various concentrations of NaSA were added to swimming plates prior to inoculation with 3 μl XKK12 WT (pPIP122) suspension (109 CFU/ml). The plates were incubated for four days at 25°C and evaluated by measuring the diameter of the swimming zone. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05). (C), Phenotype of XKK12 WT (pPIP122) on swimming plates containing 0 (left) or 1 mM NaSA (right). (D), Effects of 1 mM NaSA, 2 mM NaSA and/or 3 μM DSF on the swimming of XKK12 WT (pPIP122) and oryR knockout mutant (pPIP122) (oryR−) bacteria. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC4307914&req=5

Fig1: NaSA suppresses basal and DSF-induced swimming motility ofXanthomonas oryzaepv.oryzae(Xoo) strain XKK12 (pPIP122). (A) and (B) Various concentrations of NaSA were added to swimming plates prior to inoculation with 3 μl XKK12 WT (pPIP122) suspension (109 CFU/ml). The plates were incubated for four days at 25°C and evaluated by measuring the diameter of the swimming zone. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05). (C), Phenotype of XKK12 WT (pPIP122) on swimming plates containing 0 (left) or 1 mM NaSA (right). (D), Effects of 1 mM NaSA, 2 mM NaSA and/or 3 μM DSF on the swimming of XKK12 WT (pPIP122) and oryR knockout mutant (pPIP122) (oryR−) bacteria. Data are means ± SE. Different letters indicate statistically significant differences (Mann-Whitney: n ≥ 9; α = 0.05).
Mentions: Mounting evidence indicates that SA is an important player in the activation of rice defenses against Xoo [36,38]. In a first attempt to test whether SA also exerts direct effects on the QS machinery of Xoo, we evaluated the effect of SA on the swimming ability of Xoo strain XKK12 (pPIP122). Unless specified otherwise, this strain was routinely used throughout this paper. Since SA showed strong inhibition of bacterial growth in both liquid and solid medium in our preliminary trials, all following experiments were performed using sodium salicylate (NaSA), which had no significant impact on XKK12 growth rates on (semi-)solid agar plates (data not shown). Swim plates indicated that XKK12 is motile in swimming medium, reaching a diameter of about 20 mm after 4-6 days of incubation at 25°C. As shown in Figures 1A to 1C, NaSA at concentrations of 20 μM, 0.1 mM and 0.5 mM had little or no significant effect on the swimming ability of XKK12, whereas 1 mM and 2 mM of NaSA significantly reduced swimming. SA concentrations in basal rice leaves range from 5 to 20 μg/g fresh weight [39]. To shed light on the SA concentrations in pathogen-inoculated rice leaves, we used a previously published UPLC-MS/MS method to profile the hormone signature of Xoo-infected rice plants at various times post inoculation [40]. Consistent with previous reports, SA levels remained fairly constant throughout the course of infection, except for a late two-fold increase at 8 dpi (Additional file 1). At this time point, SA levels reached 613235 ± 12043 pmol/g FW, which corresponds to 0.767 mM SA. Supplying bacteria with 1 or 2 mM NaSA thus resembles the amount of SA encountered by Xoo in planta, demonstrating the physiological relevance of these concentrations.Figure 1

Bottom Line: Employing the rice-Xanthomonas oryzae pv. oryzae (Xoo) interaction as a model system, we show that Xoo uses the classic immune hormone salicylic acid (SA) as a trigger to activate its virulence-associated quorum sensing (QS) machinery.Despite repressing swimming motility, sodium salicylate (NaSA) induced production of the Diffusible Signal Factor (DSF) and Diffusible Factor (DF) QS signals, with resultant accumulation of xanthomonadin and extracellular polysaccharides.Moreover, we found both DF and DSF to influence SA- and ABA-responsive gene expression in planta.

View Article: PubMed Central - PubMed

Affiliation: Lab of Phytopathology, Department of Crop Protection, Ghent University, Coupure Links 653, 9000, Ghent, Belgium. jing.xu@ugent.be.

ABSTRACT

Background: Small-molecule hormones are well known to play key roles in the plant immune signaling network that is activated upon pathogen perception. In contrast, little is known about whether phytohormones also directly influence microbial virulence, similar to what has been reported in animal systems.

Results: In this paper, we tested the hypothesis that hormones fulfill dual roles in plant-microbe interactions by orchestrating host immune responses, on the one hand, and modulating microbial virulence traits, on the other. Employing the rice-Xanthomonas oryzae pv. oryzae (Xoo) interaction as a model system, we show that Xoo uses the classic immune hormone salicylic acid (SA) as a trigger to activate its virulence-associated quorum sensing (QS) machinery. Despite repressing swimming motility, sodium salicylate (NaSA) induced production of the Diffusible Signal Factor (DSF) and Diffusible Factor (DF) QS signals, with resultant accumulation of xanthomonadin and extracellular polysaccharides. In contrast, abscisic acid (ABA), which favors infection by Xoo, had little impact on DF- and DSF-mediated QS, but promoted bacterial swimming via the LuxR solo protein OryR. Moreover, we found both DF and DSF to influence SA- and ABA-responsive gene expression in planta.

Conclusions: Together our findings indicate that the rice SA and ABA signaling pathways cross-communicate with the Xoo DF and DSF QS systems and underscore the importance of bidirectional interkingdom signaling in molding plant-microbe interactions.

No MeSH data available.


Related in: MedlinePlus