Impact of Lsi1 Mutation on Lignin Accumulation and Composition in Sorghum: Implications for Bioenergy Crop Development
Researchers showed that mutating the Lsi1 Si transporter in sorghum increases lignin content in mature plants, suggesting a compensatory response for reduced silica that could be useful in developing bioenergy crops with optimized lignin and lower Si content.
Keywords: BTx623, biomass energy, lignin, low-silicon mutant, sorghum
To meet rising energy demands, biomass production for energy feedstock is crucial, with sorghum (Sorghum bicolor) emerging as a promising candidate due to its high biomass yield and resilience to drought. Sorghum is suited for diverse bioenergy products, including solid fuels like biopellets and biochar, which can potentially replace coal, thus reducing the environmental impact of thermal power generation. However, high silicon (Si) content in sorghum biomass poses a drawback, as the Si-rich ash produced during combustion can lead to furnace maintenance issues. Additionally, reducing Si content in sorghum could enhance its suitability for biofuel production, as a lower Si level also tends to increase lignin content—a beneficial trait, as lignin has a higher energy value than polysaccharides. Directly limiting Si intake is challenging due to its abundance in soil, but engineering mutants with defective Si uptake transporters, like Lsi1, may offer a solution.
In previous research, it was observed that restricting Si supply in wild-type (WT) sorghum seedlings enhanced thioglycolic acid lignin content and the S/G monomer ratio. Building on this, researchers from Kyoto University, the National Research and Innovation Agency of the Republic of Indonesia and The University of Tokyo investigated the effect of a mutation in the Lsi1 Si transporter on lignin content and composition in soil-grown, mature sorghum plants. The findings indicate that the Lsi1 mutation did not significantly impact plant growth, consistent with prior research on WT plants in limited Si conditions. However, chemical and NMR analyses revealed that the mutation led to increased lignin content in mature leaves, with elevated thioacidolysis-derived H-, G-, and S-type lignin monomers. This lignin increase was particularly notable under Si supplementation, suggesting a compensatory lignin accumulation for the absence of silica, which typically strengthens grass cell walls.
The results highlight a specific inverse relationship between lignin and Si content that is consistent across various grass species. Ultimately, these insights into lignin-Si interactions in Lsi1 mutants provide valuable implications for developing biomass crops with optimized lignin content and reduced Si for bioenergy applications.
SorghumBase examples:
Figure 1: Phylogenetic tree of LSI1 orthologs in the SorghumBase search interface shows a sorghum variety that appears to have a truncated translation in the multiple sequence alignment. Location view tabs reveal a similar gene structure to BTx623, but a deletion in PI 297155 leads to a frameshift and premature stop codon in exon 3 of SbiPI297155.04g038670.
Reference:
Rivai RR, Yamazaki K, Kobayashi M, Tobimatsu Y, Tokunaga T, Fujiwara T, Umezawa T. Altered Lignin Accumulation in Sorghum Mutated in Silicon Uptake Transporter SbLsi1. Plant Cell Physiol. 2024 Sep 30:pcae114. PMID: 39343968. doi: 10.1093/pcp/pcae114. Read more
