Silicon-mediated interactions between plant antagonists

The prolonged arms race between plants and their antagonists has resulted in the evolution of multiple plant defence mechanisms to combat attacks by pests and pathogens. Silicon (Si) accumulation occurs mainly in grasses and provides a physical barrier against antagonists. Biochemical pathways may also be involved in Si-mediated plant resistance, although the precise mode of action in this case is less clear. Most studies have focussed on Si-based effects against single attackers. In this review, we consider how Si-based plant resistance operates when simultaneously and/or sequentially attacked by insect herbivores, fungal phytopathogens, and plant parasitic nematodes and how the plant hormones jasmonic acid (JA) and salicylic acid (SA) are involved. Si defence may mediate both intra- and interspecific competition and facilitation. Si has been found to impact plant-mediated interactions between insect herbivores within the same feeding guild and across different feeding guilds, with varying patterns of JA and SA. These results suggest that hormonal crosstalk may play a role in the Si-mediated effects, although this finding varied between studies. While some reports support the notion that JA is linked to Si responses, others indicate that Si supplementation reduces JA production. In terms of phytopathogens, SA has not been found to be involved in Si-mediated defences. Improving our understanding of Si-mediated plant defence could be beneficial for sustainable agriculture under future climates.