Investigating the impact of silicon accumulation on constitutive and herbivore-induced gene expression using OsLsi1 deficient mutant rice lines

Silicon (Si) has been associated with enhanced plant defenses against various insect pests. However, the exact mechanism by which Si accumulation in rice (Oryza sativa L.) enhances rice's defenses against insects is not well understood. Thus, this study aimed to explore the impact of Si accumulation on gene expression and defense-related pathways in rice both with and without injury by Spodoptera frugiperda Smith, the fall armyworm (FAW). To examine this, we utilized three silicon transporter (OsLsi1) mutants with varying levels of Si uptake (one >95% deficient in the uptake of Si, a second ~55% deficient in the uptake of Si, and a third with uptake similar to wild-type) and compared gene expression and phytohormone levels to those in the wild-type rice cultivar Nipponbare. The results from phytohormone analysis showed that the level of jasmonic acid significantly increased due to herbivory in the leaves, regardless of the level of Si concentration in the leaves. However, we found that the level of salicylic acid did not change in response to herbivory or Si concentration. Our initial findings from RNA-Seq analysis indicated that herbivory leads to modulation of gene expression in both wild-type and Si-deficient plants. Upon preliminary functional categorization of the genes differentially expressed (DEGs) due to herbivory, it was discerned that DEGs exhibit involvement in diverse metabolic pathways, notably in phytohormone metabolism, and stress responses. This study's findings will help to clarify the role of Si in enhancing plant resistance against biotic stress, which could lead to novel plant protection methods.