MicroRNA6443‐mediated regulation of FERULATE 5‐HYDROXYLASE gene alters lignin composition and enhances saccharification in Populus tomentosa

Abstract

Summary Ferulate 5‐hydroxylase (F5H) is a limiting enzyme involved in biosynthesizing sinapyl (S) monolignol in angiosperms. Genetic regulation of F5H can influence S monolignol synthesis and therefore improve saccharification efficiency and biofuel production. To date, little is known about whether F5H is post‐transcriptionally regulated by endogenous microRNAs (miRNAs) in woody plants. Here, we report that a microRNA, miR6443, specifically regulates S lignin biosynthesis during stem development in Populus tomentosa. In situ hybridization showed that miR6443 is preferentially expressed in vascular tissues. We further identified that F5H2 is the direct target of miR6443. Overexpression of miR6443 decreased the transcript level of F5H2 in transgenic plants, resulting in a significant reduction in S lignin content. Conversely, reduced miR6443 expression by short tandem target mimics (STTM) elevated F5H2 transcripts, therefore increasing S lignin composition. Introduction of a miR6443‐resistant form of F5H2 into miR6443‐overexpression plants restored lignin ectopic composition, supporting that miR6443 specifically regulated S lignin biosynthesis by repressing F5H2 in P. tomentosa. Furthermore, saccharification assays revealed decreased hexose yields by 7.5–24.5% in miR6443‐overexpression plants compared with the wild‐type control, and increased hexoses yields by 13.2–14.6% in STTM6443‐overexpression plants. Collectively, we demonstrate that miR6443 modulates S lignin biosynthesis by specially regulating F5H2 in P. tomentosa.

Contribution of phenylpropanoid metabolism to plant development and plant–environment interactions

“…In P. tomentosa , miR6443 directly targets F5H2 , which is responsible for the biosynthesis of sinapyl monolignol. miR6443 overexpression gives rise to a decrease in the transcript level of F5H2 and a reduction in S lignin content (Fan et al, 2020).…”

Editorial: Biofuels and Bioenergy

“…In the past few decades, cell wall engineering has been a key method to reduce biomass recalcitrance by altering the structure of lignin (Sattler and Funnell-Harris, 2013 ). Perturbations of genes in the lignin biosynthetic pathway lead to major structural changes, allowing the design of easily controlled biomass structures to produce biofuels and chemicals (Zhang et al, 2019 ; Fan et al, 2020 ). In this Research Topic, Kim et al reported an integrated strategy combining biomass genetic engineering with a pretreatment using a bio-derived deep eutectic solvent (DES).…”

Knockout of the lignin pathway gene BnF5H decreases the S/G lignin composition ratio and improves S. sclerotiorum resistance in B. napus

“…Compared to the wild type and fah1 mutant, theF5H -overexpressing transgenic line significantly reduced the stiffness of the cell walls in the region of the compound middle lamella as determined by contact resonance force microscopy. Overexpression of miR6443 decreased the transcript level of F5H2 , resulting in a significant reduction in S lignin content in transgenic plants, and saccharification assays revealed decreased hexose yields by 7.5%-24.5% compared to WT (Fan et al , 2020).…”