# Silicon Protects Rice Plants Against Striped Stem Borer by Disturbing Herbivory-Induced Putrescine Accumulation

## TL;DR

Silicon helps rice plants resist striped stem borer insects by reducing the buildup of a chemical called putrescine, which is triggered by insect attacks.

## Contribution

This study reveals a novel mechanism by which silicon enhances rice resistance to insect herbivory through modulation of putrescine metabolism.

## Key findings

- Silicon application reduces putrescine accumulation in rice plants attacked by striped stem borer larvae.
- Silicon suppresses the expression of genes involved in putrescine biosynthesis triggered by insect herbivory.
- Exogenous putrescine weakens silicon-induced resistance, while an ADC inhibitor mimics silicon's protective effects.

## Abstract

Silicon (Si) protects plants against insect herbivores; however, the underlying mechanisms remain unclear. Polyamines (PAs) play a crucial role in plant–insect interactions. Here, the involvement of Si in putrescine (Put) metabolism and its role in rice resistance against striped stem borer (SSB, Chilo suppressalis Walker) were investigated. The results showed that SSB larval infestation led to a substantial accumulation of free Put in rice seedlings. Si application increased rice resistance against SSB and repressed the SSB attack-induced accumulation of Put, in parallel with a decreased expression of Put biosynthesis genes encoding arginine decarboxylase (ADC1 and ADC2). Moreover, Si application had no significant effect on the wounding-induced expression of ADC1 and ADC2, but attenuated the further elevation in the transcription of ADC1 and ADC2 induced by SSB larvae oral secretion. Simultaneously, Si addition reduced the Put and spermidine contents in SSB-attacked plants. Furthermore, the exogenous application of Put attenuated Si-enhanced resistance against SSB larvae, whereas exogenous D-arginine, an inhibitor of ADC, showed similar effects to Si on rice resistance against SSB. Our findings indicate that Si improves rice resistance to SSB, at least partly by reducing herbivory-stimulated putrescine accumulation.