Lapierre C, Sibout R, Laurans F, Lesage-Descauses MC, Déjardin A, Pilate G. p-Coumaroylation of poplar lignins impacts lignin structure and improves wood saccharification.
Plant Physiol 2021;
187:1374-1386. [PMID:
34618081 PMCID:
PMC8566233 DOI:
10.1093/plphys/kiab359]
[Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 07/16/2021] [Indexed: 05/03/2023]
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 (pCA). 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, pCA 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.
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