P-Coumaroylation of poplar lignins impacts lignin structure and improves wood saccharification. Issue 3 (7th August 2021)

• Record Type: Journal Article
• Authors: Lapierre, Catherine; Sibout, Richard; Laurans, Françoise; Lesage-Descauses, Marie-Claude; Déjardin, Annabelle; Pilate, Gilles
• Is Part Of: Plant physiology. Volume 187:Issue 3(2021)
• Page Start: 1374
• Page End: 1386
• Publication Date: 2021-08-07
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1093/plphys/kiab359
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract: The enzymatic hydrolysis of cellulose into glucose, referred to as saccharification, is severely hampered by lignins. Here, we analyzed transgenic poplars ( Populus tremula × Populus alba ) expressing the Brachypodium ( Brachypodium distachyon ) p -coumaroyl-Coenzyme A monolignol transferase 1 ( BdPMT1 ) gene driven by the Arabidopsis ( Arabidopsis thaliana ) Cinnamate 4-Hydroxylase ( AtC4H ) promoter in the wild-type (WT) line and in a line overexpressing the Arabidopsis Ferulate 5-Hydroxylase ( AtF5H ). BdPMT1 encodes a transferase which catalyzes the acylation of monolignols by p- coumaric acid ( p CA). Several BdPMT1 -OE/WT and BdPMT1 -OE /AtF5H -OE lines were grown in the greenhouse, and BdPMT1 expression in xylem was confirmed by RT-PCR. Analyses of poplar stem cell walls (CWs) and of the corresponding purified dioxan lignins (DLs) revealed that BdPMT1 -OE lignins were as p -coumaroylated as lignins from C3 grass straws. For some transformants, p CA levels reached 11 mg·g −1 CW and 66 mg·g −1 DL, exceeding levels in Brachypodium or wheat ( Triticum aestivum ) samples. This unprecedentedly high lignin p- coumaroylation affected neither poplar growth nor stem lignin content. Interestingly, p -coumaroylation of poplar lignins was not favored in BdPMT1 -OE/ AtF5H -OE transgenic lines despite their high frequency of syringyl units. However, lignins of all BdPMT1 -OE lines were structurally modified, with an increase of terminal unit with free phenolic groups. Relative to controls, this increase argues for a reduced polymerization degree of BdPMT1 -OE lignins and makes them more soluble in cold NaOH solution. The p -coumaroylation of poplar samples improved the saccharification yield of alkali-pretreated CW, demonstrating that the genetically driven p -coumaroylation of lignins is a promising strategy to make wood lignins more susceptible to alkaline treatments used during the industrial processing of lignocellulosics. Abstract : The expression of a grass p -coumaroyl-CoA:monolignol transferase induces high p -coumaroylation of poplar lignins and better saccharification of alkali-pretreated poplar wood without growth penalty.