Altered Lignin Accumulation in Sorghum Mutated in Silicon Uptake Transporter SbLsi1

Sorghum [Sorghum bicolor (L.) Moench] has been receiving attention as a feedstock for lignocellulose biomass energy. During the combustion process, ash-containing silicon (Si) can be produced, which causes problems in furnace maintenance. Hence, lowering Si content in plants is crucial. However, limiting Si supply to crops is difficult in practice because Si is abundant in the soil. Previously, an Si uptake transporter (SbLsi1) has been identified, and an Si-depleted mutant has also been generated in the model sorghum variety BTx623. In this study, we aimed to investigate the changes induced by a mutation in SbLsi1 on the accumulation and structure of lignin in cell walls. Through chemical and NMR analyses, we demonstrated that the lsi1 mutation resulted in a significant increase in lignin accumulation levels as well as a significant reduction in Si content. At least some of the modification was induced by transcriptional changes, as suggested by the upregulation of phenylpropanoid biosynthesis-related genes in the mutant plants. These findings derived from the model variety could be useful for the future development of practical cultivars with high biomass and less Si content for bioenergy applications.