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

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 upregulated 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.Erysiphe cichoracearum ͉ microarray ͉ transcriptome

Callose-associated silica deposition in Arabidopsis

“…We have been able to show a clear if qualitative relationship between the induction of callose and deposition of biogenic silica in Arabidopsis, a plant not known for accumulating significant amounts of silica in its leaves. Our results for callose induction strongly support research identifying a role for callose in resistance to powdery mildew in Arabidopsis [4] while our findings for silica deposition suggest a mechanism for silicon-induced resistance to the same pathogen in Arabidopsis [7,8]. We reported previously that callose-associated silica deposition provided protection against powdery mildew in Equisetum arvense (horsetail) and 8 we speculated that biogenic silica presented a physical barrier to the entry of the pathogen [3].…”

Laser microdissection of Arabidopsis cells at the powdery mildew infection site reveals site-specific processes and regulators

“…TFs often exhibit low-level and highly localized expression changes; therefore, we expected our site-specific expression analysis to identify unique TFs with important functional roles in the PM interaction. We found 67 TFs exhibited altered expression at the site of infection, with 79% not previously associated with a compatible PM interaction (4,(7)(8)(9). Although many of these PM site-specific TFs have no defined function, we identified sets of TFs associated with the following processes: photosynthesis, drought/cold tolerance, pathogen defense and cell death, auxin signaling/response, and the cell cycle (Fig.…”

“…3A and SI Appendix). Although a decrease in photosynthesis-associated gene expression had previously been observed in whole leaves in response to PM (4,7,11), our focus at the site of infection allowed us to identify a more extensive set of altered photosynthesis-related genes. It also eliminated potential complications associated with differential PM-induced impacts on photosynthesis at the site of infection compared with nearby or distal sites.…”

The role of silicon (Si) in increasing plant resistance against fungal diseases

“…A study by Kauss et al (2003) conducted on cucumber leaves and investigating the process of plant infection showed that resistance to infection can be acquired by the expression of a protein rich in proline together with the presence of silica at the site of pathogen penetration. Fauteux et al (2006) stated that only two genes were upregulated when silicon alone was applied to Arabidopsis plants. Brunings et al (2009) studied the gene expression of silicon-treated rice using a microarray and found diff erential regulation of 221 genes compared to untreated control, including some transcription factors.…”

“…By using Agilent 44K oligo DNA arrays, it has been shown that silicon increased signifi cantly the level of photorespiration in rice leaves infected by Cochliobolus miyabeanus (Van Bockhaven et al, 2014). Genome-wide studies on tomato, rice, Arabidopsis and wheat grown in soil amended with silicon and compared to non-amended control plants have shown a diff erential and unique expression of a large number of genes involved in host plant defense mechanisms or metabolism (Watanabe et al, 2004;Fauteux et al, 2006;Chain et al, 2009;Brunings et al, 2009;Ghareeb et al, 2011).…”