Silicon protects soybean plants against <italic>Phytophthora sojae</italic> by interfering with effector-receptor expression.

Background: Silicon (Si) is known to protect against biotrophic and hemibiotrophic plant pathogens; however, the mechanisms by which it exerts its prophylactic role remain unknown. In an attempt to obtain unique insights into the mode of action of Si, we conducted a full comparative transcriptomic analysis of soybean (<italic>Glycine max</italic>) plants and <italic>Phytophthora sojae</italic>, a hemibiotroph that relies heavily on effectors for its virulence. Results: Supplying Si to inoculated plants provided a strong protection against <italic>P. sojae</italic> over the course of the experiment (21 day). Our results showed that the response of Si-free (Si⁻) plants to inoculation was characterized early (4 dpi) by a high expression of defense-related genes, including plant receptors, which receded over time as the pathogen progressed into the roots. The infection was synchronized with a high expression of effectors by <italic>P. sojae</italic>, the nature of which changed over time. By contrast, the transcriptomic response of Si-fed (Si⁺) plants was remarkably unaffected by the presence of <italic>P. sojae</italic>, and the expression of effector-coding genes by the pathogen was significantly reduced. Conclusion: Given that the apoplast is a key site of interaction between effectors and plant defenses and receptors in the soybean-<italic>P. sojae</italic> complex, as well as the site of amorphous-Si accumulation, our results indicate that Si likely interferes with the signaling network between <italic>P. sojae</italic> and the plant, preventing or decreasing the release of effectors reaching plant receptors, thus creating a form of incompatible interaction. [ABSTRACT FROM AUTHOR]