Silicon amendment to rice plants contributes to reduced feeding in a phloem‐sucking insect through modulation of callose deposition

Abstract

Silicon (Si) uptake by Poaceae plants has beneficial effects on herbivore defense. Increased plant physical barrier and altered herbivorous feeding behaviors are documented to reduce herbivorous arthropod feeding and contribute to enhanced plant defense. Here, we show that Si amendment to rice (Oryza sativa) plants contributes to reduced feeding in a phloem feeder, the brown planthopper (Nilaparvata lugens, BPH), through modulation of callose deposition. We associated the temporal dynamics of BPH feeding with callose deposition on sieve plates and further with callose synthase and hydrolase gene expression in plants amended with Si. Biological assays revealed that BPH feeding was lower in Si‐amended than in nonamended plants in the early stages post‐BPH infestation. Histological observation showed that BPH infestation triggered fast and strong callose deposition in Si‐amended plants compared with nonamended plants. Analysis using qRT‐PCR revealed that expression of the callose synthase gene OsGSL1 was up‐regulated more and that the callose hydrolase (β‐1,3‐glucanase) gene Gns5 was up‐regulated less in Si‐amended than in nonamended plants during the initial stages of BPH infestation. These dynamic expression levels of OsGSL1 and Gns5 in response to BPH infestation correspond to callose deposition patterns in Si‐amended versus nonamended plants. It is demonstrated here that BPH infestation triggers differential gene expression associated with callose synthesis and hydrolysis in Si‐amended and nonamended rice plants, which allows callose to be deposited more on sieve tubes and sieve tube occlusions to be maintained more thus contributing to reduced BPH feeding on Si‐amended plants.

Current understanding of the molecular players involved in resistance to rice planthoppers

“…A BPH‐susceptible rice variety growing in a nutrient solution containing Na 2 SiO 3 ·9H 2 O had 98% greater resistance than rice in a nutrient solution without addition of Na 2 SiO 3 ·9H 2 O. Under laboratory conditions, such a silicon amendment improved silicification of leaf sheaths forming a physical barrier and increased the leaf rigidity but reduced the digestibility of plant tissues . Biochar has been reported to induce resistance against WBPH under laboratory conditions.…”

“…Attempts have also been made to develop additional environmentally friendly and economically sound alternative measures for planthopper control. The amendment of rice paddies with substances such as silicon and biochar are potential alternatives . A BPH‐susceptible rice variety growing in a nutrient solution containing Na 2 SiO 3 ·9H 2 O had 98% greater resistance than rice in a nutrient solution without addition of Na 2 SiO 3 ·9H 2 O.…”

“…The amendment of rice paddies with substances such as silicon and biochar are potential alternatives. 3,4 A BPH-susceptible rice variety growing in a nutrient solution containing Na 2 SiO 3 ·9H 2 O had 98% greater resistance than rice in a nutrient solution without addition of Na 2 SiO 3 ·9H 2 O. Under laboratory conditions, such a silicon amendment improved silicification of leaf sheaths forming a physical barrier and increased the leaf rigidity but reduced the digestibility of plant tissues.…”

“…The growing concern of the durability of the host‐plant resistance has prompted the need to develop more attractive approaches, such as integrated control techniques . Moreover, regarding efficiency and sustainability in the current post‐green revolution era, effective and economical methods such as the use of chemical elicitors or amendment with biochar and silicon to enhance the resistance of rice are currently receiving attention …”

“…2 Moreover, regarding efficiency and sustainability in the current post-green revolution era, effective and economical methods such as the use of chemical elicitors or amendment with biochar and silicon to enhance the resistance of rice are currently receiving attention. 3,4 A better understanding of the molecules responsible for resistance to rice planthoppers is imperative for improving the practices for control of these pests. In the past decade, increasing data on the interaction between planthoppers and rice plants has led to the identification of the molecules that are involved in resistance to rice planthoppers.…”