Silicon supplementation improves biomass and direct defense of ryegrass: A multi-omics study

Abstract

Silicon (Si) has the potential to promote plant yield and improve their insect resistance, but the direct defense mechanisms associated with the effects of Si on forage grasses and its regulation are not known. In this study, the conditions of silica fertilization nutrition (1 and 3 mmol L−1 recorded as low concentration (LC) and high concentration (HC) groups, respectively) were changed during the seed germination period, which did not significantly affect the seed germination of ryegrass. However, the shoot biomass and insect resistance of ryegrass were significantly increased in the HC group. Comparison of the transcriptional results from RNA-seq assays revealed that the accumulation of ryegrass biomass may be closely related to the silicon intervention in photosynthesis, and the metabolic synthesis of lignin, carbohydrates, and hemicellulose. There was an additive effect of silicon concentration on the regulatory effects of ryegrass at the transcriptional level. Meanwhile, 98 and 1291 differentially expressed genes were assigned to the metabolic process in the LC and HC groups, respectively. Metabolomic results combined with LC-MS analysis showed that Si initiated a direct defense network in ryegrass with Phenylpropanoid biosynthesis as the backbone, and Flavonoid, Flavone and flavonol, and Isoflavonoid biosynthesis as important branches. The relative content of phenolics was significantly up-regulated, especially in the HC group, and most of these phenolics were potent SOS substances, closely related to the physiological disturbances suffered by Spodoptera frugiperda, with inhibitory effects on larval body weight. The above results confirm that silicon promotes an increase in ryegrass yield while initiating its direct defense network against insects, and that silicon is an effective supplement in improving ryegrass yield and insect resistance.