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The microbe-secreted isopeptide poly- γ -glutamic acid induces stress tolerance in Brassica napus L. seedlings by activating crosstalk between H 2 O 2 and Ca 2+

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ABSTRACT

Poly-γ-glutamic acid (γ-PGA) is a microbe-secreted isopeptide that has been shown to promote growth and enhance stress tolerance in crops. However, its site of action and downstream signaling pathways are still unknown. In this study, we investigated γ-PGA-induced tolerance to salt and cold stresses in Brassica napus L. seedlings. Fluorescent labeling of γ-PGA was used to locate the site of its activity in root protoplasts. The relationship between γ-PGA-induced stress tolerance and two signal molecules, H2O2 and Ca2+, as well as the γ-PGA-elicited signaling pathway at the whole plant level, were explored. Fluorescent labeling showed that γ-PGA did not enter the cytoplasm but instead attached to the surface of root protoplasm. Here, it triggered a burst of H2O2 in roots by enhancing the transcription of RbohD and RbohF, and the elicited H2O2 further activated an influx of Ca2+ into root cells. Ca2+ signaling was transmitted via the stem from roots to leaves, where it elicited a fresh burst of H2O2, thus promoting plant growth and enhancing stress tolerance. On the basis of these observation, we propose that γ-PGA mediates stress tolerance in Brassica napus seedlings by activating an H2O2 burst and subsequent crosstalk between H2O2 and Ca2+ signaling.

No MeSH data available.


Changes in H2O2 content in Brassica napus seedling roots after treatment with poly-γ-glutamic acid (γ-PGA).(A) Changes in the H2O2 content of roots following application of γ-PGA. (B) Dichloro-dihydro-fluorescein diacetate (DCFH-DA) fluorescence images of rape seedling roots after treatment with γ-PGA.
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f3: Changes in H2O2 content in Brassica napus seedling roots after treatment with poly-γ-glutamic acid (γ-PGA).(A) Changes in the H2O2 content of roots following application of γ-PGA. (B) Dichloro-dihydro-fluorescein diacetate (DCFH-DA) fluorescence images of rape seedling roots after treatment with γ-PGA.

Mentions: H2O2 levels in roots were significantly increased after the application of γ-PGA (Fig. 3A). At day 1 post-treatment, H2O2 increased rapidly to a peak, and then gradually decreased over the subsequent days, although it continued to remain at a significantly higher level than in the control. The staining patterns of dichloro-dihydro-fluorescein diacetate (DCFH-DA: a fluorescent dye used for detecting H2O2) in the root tips were consistent with these measured results (Fig. 3B). Following treatment with γ-PGA, all of the tested root tips showed brighter fluorescence than the control, with the greatest intensity being observed in the tip at 1 day post γ-PGA treatment. In the control group, all root tips sampled on different days showed considerably weaker fluorescence and differences among the different samples were non-significant. Accordingly, only one image of these control roots has been shown in Fig. 3B.


The microbe-secreted isopeptide poly- γ -glutamic acid induces stress tolerance in Brassica napus L. seedlings by activating crosstalk between H 2 O 2 and Ca 2+
Changes in H2O2 content in Brassica napus seedling roots after treatment with poly-γ-glutamic acid (γ-PGA).(A) Changes in the H2O2 content of roots following application of γ-PGA. (B) Dichloro-dihydro-fluorescein diacetate (DCFH-DA) fluorescence images of rape seedling roots after treatment with γ-PGA.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304171&req=5

f3: Changes in H2O2 content in Brassica napus seedling roots after treatment with poly-γ-glutamic acid (γ-PGA).(A) Changes in the H2O2 content of roots following application of γ-PGA. (B) Dichloro-dihydro-fluorescein diacetate (DCFH-DA) fluorescence images of rape seedling roots after treatment with γ-PGA.
Mentions: H2O2 levels in roots were significantly increased after the application of γ-PGA (Fig. 3A). At day 1 post-treatment, H2O2 increased rapidly to a peak, and then gradually decreased over the subsequent days, although it continued to remain at a significantly higher level than in the control. The staining patterns of dichloro-dihydro-fluorescein diacetate (DCFH-DA: a fluorescent dye used for detecting H2O2) in the root tips were consistent with these measured results (Fig. 3B). Following treatment with γ-PGA, all of the tested root tips showed brighter fluorescence than the control, with the greatest intensity being observed in the tip at 1 day post γ-PGA treatment. In the control group, all root tips sampled on different days showed considerably weaker fluorescence and differences among the different samples were non-significant. Accordingly, only one image of these control roots has been shown in Fig. 3B.

View Article: PubMed Central - PubMed

ABSTRACT

Poly-γ-glutamic acid (γ-PGA) is a microbe-secreted isopeptide that has been shown to promote growth and enhance stress tolerance in crops. However, its site of action and downstream signaling pathways are still unknown. In this study, we investigated γ-PGA-induced tolerance to salt and cold stresses in Brassica napus L. seedlings. Fluorescent labeling of γ-PGA was used to locate the site of its activity in root protoplasts. The relationship between γ-PGA-induced stress tolerance and two signal molecules, H2O2 and Ca2+, as well as the γ-PGA-elicited signaling pathway at the whole plant level, were explored. Fluorescent labeling showed that γ-PGA did not enter the cytoplasm but instead attached to the surface of root protoplasm. Here, it triggered a burst of H2O2 in roots by enhancing the transcription of RbohD and RbohF, and the elicited H2O2 further activated an influx of Ca2+ into root cells. Ca2+ signaling was transmitted via the stem from roots to leaves, where it elicited a fresh burst of H2O2, thus promoting plant growth and enhancing stress tolerance. On the basis of these observation, we propose that γ-PGA mediates stress tolerance in Brassica napus seedlings by activating an H2O2 burst and subsequent crosstalk between H2O2 and Ca2+ signaling.

No MeSH data available.