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. 2006 Nov 14;103(46):17554-9.
doi: 10.1073/pnas.0606330103. Epub 2006 Nov 2.

The protective role of silicon in the Arabidopsis-powdery mildew pathosystem

François Fauteux  1 , Florian Chain, François Belzile, James G Menzies, Richard R Bélanger
Affiliations

The protective role of silicon in the Arabidopsis-powdery mildew pathosystem

François Fauteux et al. Proc Natl Acad Sci U S A. .

Abstract

The role and essentiality of silicon (Si) in plant biology have been debated for >150 years despite numerous reports describing its beneficial properties. To obtain unique insights regarding the effect of Si on plants, we performed a complete transcriptome analysis of both control and powdery mildew-stressed Arabidopsis plants, with or without Si application, using a 44K microarray. Surprisingly, the expression of all but two genes was unaffected by Si in control plants, a result contradicting reports of a possible direct effect of Si as a fertilizer. In contrast, inoculation of plants, treated or not with Si, altered the expression of a set of nearly 4,000 genes. After functional categorization, many of the up-regulated genes were defense-related, whereas a large proportion of down-regulated genes were involved in primary metabolism. Regulated defense genes included R genes, stress-related transcription factors, genes involved in signal transduction, the biosynthesis of stress hormones (SA, JA, ethylene), and the metabolism of reactive oxygen species. In inoculated plants treated with Si, the magnitude of down-regulation was attenuated by >25%, an indication of stress alleviation. Our results demonstrate that Si treatment had no effect on the metabolism of unstressed plants, suggesting a nonessential role for the element but that it has beneficial properties attributable to modulation of a more efficient response to pathogen stress.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Si treatment and powdery mildew of Arabidopsis. (a) Powdery mildew colonies of E. cichoracearum on Arabidopsis leaves. (b) Scanning electron microscopy of mycelial mat on control (Left) and Si-treated (Right) leaves. (c) X-ray microanalysis for Si detection in control (Left) and Si-treated (Right) plants; the concentration of Si is indicated by color (see Inset), where red represents the highest concentration of Si and black indicates no Si.
Fig. 2.
Fig. 2.
Differential gene expression in Arabidopsis leaves after Si treatment and/or pathogen inoculation. The columns represent the contrasts between the treatments: control (C), silicon (Si), E. cichoracearum (P), or a combination of both (Si-P). Each of the 3,970 differentially expressed genes (P < 0.01, ≥1.5-fold change) in at least one contrast is represented by a colored line indicating the mean (n = 6) relative transcript level: green corresponds to a log2 ratio of −2 (down-regulation), and red corresponds to a log2 ratio of 2 (up-regulation).
Fig. 3.
Fig. 3.
Differentially expressed genes in Arabidopsis leaves and related to defense reactions and associated expression profiles. The columns represent some contrasts between the treatments: control (C), silicon (Si), E. cichoracearum (P), or a combination of both (Si-P). Among regulated genes, 616 were classified as plant defense-related. Each one of these genes (P < 0.01, ≥1.5-fold change) in at least one contrast is represented by a colored line indicating the mean relative transcript level (n = 6): green corresponds to a log2 ratio of −2 (down-regulation), and red corresponds to a log2 ratio of 2 (up-regulation).
Fig. 4.
Fig. 4.
Differentially expressed genes in Arabidopsis leaves related to primary metabolism and cellular processes and associated expression profiles. The columns represent some contrasts between the treatments: control (C), silicon (Si), E. cichoracearum (P), or a combination of both (Si-P). Among regulated genes, 2,089 were classified as related to plant metabolism or cellular processes. Each one of these genes (P < 0.01, ≥1.5-fold change) in at least one contrast is represented by a colored line indicating the mean relative transcript level (n = 6): green corresponds to a log2 ratio of −2 (down-regulation), and red corresponds to a log2 ratio of 2 (up-regulation).
Fig. 5.
Fig. 5.
Correlation between microarray and quantitative real-time PCR data. Log2 of fold change determined by microarray (y axis) and quantitative real-time PCR (x axis) are plotted for a subset of 10 differentially expressed genes in Arabidopsis leaves.
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