Open Collections

Kuo, Chak Chung

University of British Columbia

Lignin is a rigid, hydrophobic polymer that strengthens the cell wall of supportive fibres and water-conducting vessels in vascular plants. Four main stages of lignification include: (1) monolignol production in the cytosol via the phenylpropanoid pathway, activated by MYB58 and MYB63 transcription factors; (2) monolignol diffusion into the cell wall; (3) monolignol radicalization by laccases (LACs) and/or peroxidases (PRXs); and (4) radical coupling of monolignols into polymeric lignin. Disrupting monolignol production or mutating oxidative enzymes often leads to improper plant development or dwarfism, suggesting that the quantity and location of lignin in the cell wall must be tightly regulated. It remains unclear how plants balance monolignol production and oxidative enzyme activity to coordinate proper lignification and plant development. In this study, Arabidopsis plants that overexpress MYB63 in xylem vessels and interfascicular fibres have increased stem lignin content without growth penalty. This suggests that a moderate increase in metabolic flux through the phenylpropanoid pathway leads to hyperlignification in lignifying cell types that possess the necessary molecular machinery for lignification. To understand how oxidative enzymes in distinct cell wall domains contribute to lignification, higher order mutants of LACs and PRXs were created with CRISPR/Cas9. Mutating genes encoding secondary cell wall-localized LAC4, LAC17, and PRX72 led to more irregular vessels and less stem lignin than the lac4-2 lac17 double mutant without additional growth penalty; mutating genes encoding cell corner/middle lamella-localized LAC4 and PRX64 led to shorter stems compared to the lac4-2 single mutant. This suggests that vessel irregularity does not contribute to lignin modification-induced dwarfism. The ability to modulate the quantity and distribution of lignin without growth penalty will provide insights into engineering low-lignin plants for more efficient conversion of cellulose to biofuels, and high-lignin plants for valuable phenolic-derived bioproducts.

Text

2024-01-10

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87192

Botany

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/