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The interaction of Arabidopsis with Piriformospora indica shifts from initial transient stress induced by fungus-released chemical mediators to a mutualistic interaction after physical contact of the two symbionts.

Vahabi K, Sherameti I, Bakshi M, Mrozinska A, Ludwig A, Reichelt M, Oelmüller R - BMC Plant Biol. (2015)

Bottom Line: Once a physical contact is established, the stomata re-open, ROS and phytohormone levels decline, and the number and expression level of defense/stress-related genes decreases.We propose that exudated compounds from P. indica induce stress and defense responses in the host.Root colonization results in the down-regulation of defense responses and the activation of genes involved in promoting plant growth, metabolism and performance.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Piriformospora indica, an endophytic fungus of Sebacinales, colonizes the roots of many plant species including Arabidopsis thaliana. The symbiotic interaction promotes plant performance, growth and resistance/tolerance against abiotic and biotic stress.

Results: We demonstrate that exudated compounds from the fungus activate stress and defense responses in the Arabidopsis roots and shoots before the two partners are in physical contact. They induce stomata closure, stimulate reactive oxygen species (ROS) production, stress-related phytohormone accumulation and activate defense and stress genes in the roots and/or shoots. Once a physical contact is established, the stomata re-open, ROS and phytohormone levels decline, and the number and expression level of defense/stress-related genes decreases.

Conclusions: We propose that exudated compounds from P. indica induce stress and defense responses in the host. Root colonization results in the down-regulation of defense responses and the activation of genes involved in promoting plant growth, metabolism and performance.

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NRT2.5induction in the roots and shoots of Arabidopsis seedlings which were exposed toP. indicafor either two or six days. The fold change relative to the mock-treatment is presented. Based on 3 independent biological experiments with 3 technical replicates each. Bars are SEs; they represent the sum of the SEs of the individual values. Asterisks indicate significant differences (six day shoot value vs. two day shoot value), as determined by Student’s t-test (**P < 0.01).
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Fig3: NRT2.5induction in the roots and shoots of Arabidopsis seedlings which were exposed toP. indicafor either two or six days. The fold change relative to the mock-treatment is presented. Based on 3 independent biological experiments with 3 technical replicates each. Bars are SEs; they represent the sum of the SEs of the individual values. Asterisks indicate significant differences (six day shoot value vs. two day shoot value), as determined by Student’s t-test (**P < 0.01).

Mentions: NRT2.5 belongs to the nitrate transporter family and is preferentially, but not exclusively, expressed in leaves. The protein plays an essential role in plant growth promotion by the rhizospheric bacterium strain Phyllobacterium brassicacearum STM196 [13,14]. The regulation of its mRNA level in the leaves appears to be very sensitive to signals from the roots. Figure 3 demonstrates that the mRNA level for NRT2.5 in the roots is ~ 4-6-fold up-regulated by P. indica, two and six days after co-cultivation. Furthermore, while no significant response can be detected in the leaves two days after co-cultivation, a ~4-fold up-regulation is observed six days after co-cultivation of the seedlings with P. indica. This shows that signals from the fungus are transferred to the leaves, although the response is slower than this for stomata closure (Figure 1) and ROS production (Figure 2). The NRT2.5 mRNA levels in the roots and leaves on split Petri dish experiments were not up-regulated in comparison to the mock-treated controls (data not shown) which again demonstrates that the NTR2.5 response is mediated by fungus-derived non-gaseous chemical mediators.Figure 3


The interaction of Arabidopsis with Piriformospora indica shifts from initial transient stress induced by fungus-released chemical mediators to a mutualistic interaction after physical contact of the two symbionts.

Vahabi K, Sherameti I, Bakshi M, Mrozinska A, Ludwig A, Reichelt M, Oelmüller R - BMC Plant Biol. (2015)

NRT2.5induction in the roots and shoots of Arabidopsis seedlings which were exposed toP. indicafor either two or six days. The fold change relative to the mock-treatment is presented. Based on 3 independent biological experiments with 3 technical replicates each. Bars are SEs; they represent the sum of the SEs of the individual values. Asterisks indicate significant differences (six day shoot value vs. two day shoot value), as determined by Student’s t-test (**P < 0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4384353&req=5

Fig3: NRT2.5induction in the roots and shoots of Arabidopsis seedlings which were exposed toP. indicafor either two or six days. The fold change relative to the mock-treatment is presented. Based on 3 independent biological experiments with 3 technical replicates each. Bars are SEs; they represent the sum of the SEs of the individual values. Asterisks indicate significant differences (six day shoot value vs. two day shoot value), as determined by Student’s t-test (**P < 0.01).
Mentions: NRT2.5 belongs to the nitrate transporter family and is preferentially, but not exclusively, expressed in leaves. The protein plays an essential role in plant growth promotion by the rhizospheric bacterium strain Phyllobacterium brassicacearum STM196 [13,14]. The regulation of its mRNA level in the leaves appears to be very sensitive to signals from the roots. Figure 3 demonstrates that the mRNA level for NRT2.5 in the roots is ~ 4-6-fold up-regulated by P. indica, two and six days after co-cultivation. Furthermore, while no significant response can be detected in the leaves two days after co-cultivation, a ~4-fold up-regulation is observed six days after co-cultivation of the seedlings with P. indica. This shows that signals from the fungus are transferred to the leaves, although the response is slower than this for stomata closure (Figure 1) and ROS production (Figure 2). The NRT2.5 mRNA levels in the roots and leaves on split Petri dish experiments were not up-regulated in comparison to the mock-treated controls (data not shown) which again demonstrates that the NTR2.5 response is mediated by fungus-derived non-gaseous chemical mediators.Figure 3

Bottom Line: Once a physical contact is established, the stomata re-open, ROS and phytohormone levels decline, and the number and expression level of defense/stress-related genes decreases.We propose that exudated compounds from P. indica induce stress and defense responses in the host.Root colonization results in the down-regulation of defense responses and the activation of genes involved in promoting plant growth, metabolism and performance.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Piriformospora indica, an endophytic fungus of Sebacinales, colonizes the roots of many plant species including Arabidopsis thaliana. The symbiotic interaction promotes plant performance, growth and resistance/tolerance against abiotic and biotic stress.

Results: We demonstrate that exudated compounds from the fungus activate stress and defense responses in the Arabidopsis roots and shoots before the two partners are in physical contact. They induce stomata closure, stimulate reactive oxygen species (ROS) production, stress-related phytohormone accumulation and activate defense and stress genes in the roots and/or shoots. Once a physical contact is established, the stomata re-open, ROS and phytohormone levels decline, and the number and expression level of defense/stress-related genes decreases.

Conclusions: We propose that exudated compounds from P. indica induce stress and defense responses in the host. Root colonization results in the down-regulation of defense responses and the activation of genes involved in promoting plant growth, metabolism and performance.

Show MeSH