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Summary Grass lignocelluloses feature complex compositions and structures. In addition to the presence of conventional lignin units from monolignols, acylated monolignols and flavonoid tricin also incorporate into lignin polymer; moreover, hydroxycinnamates, particularly ferulate, cross‐link arabinoxylan chains with each other and/or with lignin polymers. These structural complexities make grass lignocellulosics difficult to optimize for effective agro‐industrial applications. In the present study, we assess the applications of two engineered monolignol 4‐O‐methyltransferases (MOMTs) in modifying rice lignocellulosic properties. Two MOMTs confer regiospecific para‐methylation of monolignols but with different catalytic preferences. The expression of MOMTs in rice resulted in differential but drastic suppression of lignin deposition, showing more than 50% decrease in guaiacyl lignin and up to an 90% reduction in syringyl lignin in transgenic lines. Moreover, the levels of arabinoxylan‐bound ferulate were reduced by up to 50%, and the levels of tricin in lignin fraction were also substantially reduced. Concomitantly, up to 11 μmol/g of the methanol‐extractable 4‐O‐methylated ferulic acid and 5–7 μmol/g 4‐O‐methylated sinapic acid were accumulated in MOMT transgenic lines. Both MOMTs in vitro displayed discernible substrate promiscuity towards a range of phenolics in addition to the dominant substrate monolignols, which partially explains their broad effects on grass phenolic biosynthesis. The cell wall structural and compositional changes resulted in up to 30% increase in saccharification yield of the de‐starched rice straw biomass after diluted acid‐pretreatment. These results demonstrate an effective strategy to tailor complex grass cell walls to generate improved cellulosic feedstocks for the fermentable sugar‐based production of biofuel and bio‐chemicals.

Ester‐linked p ‐hydroxybenzoate occurs naturally in poplar lignin as pendent groups that can be released by mild alkaline hydrolysis. These ‘clip‐off’ phenolics can be separated from biomass and upgraded into diverse high‐value bioproducts. We introduced a bacterial chorismate pyruvate lyase gene into transgenic poplar trees with the aim of producing more p ‐hydroxybenzoate from chorismate, itself a metabolic precursor to lignin. By driving heterologous expression specifically in the plastids of cells undergoing secondary wall formation, this strategy achieved a 50% increase in cell‐wall‐bound p ‐hydroxybenzoate in mature wood and nearly 10 times more in developing xylem relative to control trees. Comparable amounts also remained as soluble p ‐hydroxybenzoate‐containing xylem metabolites, pointing to even greater engineering potential. Mass spectrometry imaging showed that the elevated p ‐hydroxybenzoylation was largely restricted to the cell walls of fibres. Finally, transgenic lines outperformed control trees in assays of saccharification potential. This study highlights the biotech potential of cell‐wall‐bound phenolate esters and demonstrates the importance of substrate supply in lignin engineering.

Woody biomass is a promising source of fermentable sugars for biofuels and bio‐based chemicals, but its industrial use is limited by the costly biorefinery process. A viable strategy to reduce costs involves enhancing both biomass processability and the generation of high‐value co‐products. Here, we report the implementation of a synthetic metabolic pathway in Populus tremula  ×  P. alba to produce 2‐pyrone‐4,6‐dicarboxylic acid (PDC), a key building block for biodegradable plastics and high‐performance materials. This artificial pathway—comprising microbial genes AroG , QsuB , PmdA , PmdB , and PmdC —enabled de novo PDC production in the stems of transgenic poplar. Pathway expression also induced substantial metabolic reprogramming and altered cell wall composition. These include the hyperaccumulation of simple phenolics like protocatechuic acid (PCA) and vanillic acid (VA), alongside reduced levels of p ‐hydroxybenzoic acid. A large portion of VA was ester‐linked to cell wall lignin, while PCA was incorporated into the lignin backbone, forming novel benzodioxane units; concurrently, lignin in transgenic plants exhibited a drastic reduction in guaiacyl‐ and syringyl‐units, with a notable increase in p ‐hydroxyphenyl‐units. Hemicellulose content, particularly xylan, was also significantly increased. Moreover, expression of the PDC‐pathway led to the formation of novel VA‐derived suberin aromatics, enhancing suberization in bark and roots and improving salt stress tolerance. These changes led to improved saccharification efficiency, with up to 25% more glucose and 2.5 times xylose released from woody biomass. These results demonstrate the metabolic flexibility of poplar and highlight its potential for engineering cost‐effective, stress‐resilient bioenergy crops with enhanced biorefinery traits.

Suberin, a polyester polymer in the cell wall of terrestrial plants, controls the transport of water and nutrients and protects plant from pathogenic infections and environmental stresses. Structurally, suberin consists of aliphatic and aromatic domains; p-hydroxycinnamates, such as ferulate, p-coumarate, and/or sinapate, are the major phenolic constituents of the latter. By analyzing the \"wall-bound\" phenolics of mutant lines of Arabidopsis deficient in a family of acyl-CoA dependent acyltransferase (BAHD) genes, we discovered that the formation of aromatic suberin in Arabidopsis, primarily in seed and root tissues, depends on a member of the BAHD superfamily of enzymes encoded by At5g41040. This enzyme exhibits an ω-hydroxyacid hydroxycinnamoyltransferase activity with an in vitro kinetic preference for feruloyl-CoA and 16-hydroxypalmitic acid. Knocking down or knocking out the At5g41040 gene in Arabidopsis reduces specifically the quantity of ferulate in suberin, but does not affect the accumulation of p-coumarate or sinapate. The loss of the suberin phenolic differentially affects the aliphatic monomer loads and alters the permeability and sensitivity of seeds and roots to salt stress. This highlights the importance of suberin aromatics in the polymer's function.

Knowledge of the effect of different copper (Cu) chemical forms and their application mode on meeting the plant’s Cu requirement is much more limited than that of other micronutrients. In this work, hydroponically-grown tobacco ( Nicotiana rustica L . ) plants were pre-cultured for thirty days under Cu-sufficient and Cu-deficient conditions, then the Cu-deficient plants were resupplied with 0.5 µM CuSO 4 (CuSu) or Cu tetraamine sulfate complex ([Cu(NH 3 ) 4 ]SO 4 ) (CuAm) through roots or leaves. The biomass of plants was resumed almost equally by both chemical forms of Cu. Cu’s leaf and root concentrations exhibited a more pronounced response to CuSu application. In contrast, the restoration of the activities of Cu-containing enzymes (superoxide dismutase, polyphenol oxidase, diamine oxidase) was either similar to or, in some cases, even higher when CuAm was applied. The leaf iron concentration was also diminished under Cu starvation and increased by Cu resupply more effectively by CuAm. The activity of phenylalanine ammonia-lyase and peroxidase, phenolics accumulation, and lignin deposition was significantly influenced by Cu deficiency and resupply. Foliar-applied CuAm and root-applied CuSu were the most effective treatments for the resumption of lignin concentration. Results showed efficient re-translocation of foliar-applied Cu. However, the activity of defense enzymes and lignin content suggests that foliar spraying likely induced mechanical stress in the leaves. Furthermore, the effect of the accompanying ion (NH 4 + ) was likely the mechanism for the superior effect of CuAm in the induction of structural strength through lignin deposition and improvement of Fe uptake in plants compared with CuSu.

The present study aimed at identifying the regions of triticale genome responsible for cell wall saturation with phenolic compounds under drought stress during vegetative and generative growth. Moreover, the loci determining the activity of the photosynthetic apparatus, leaf water content (LWC) and osmotic potential ( Ψ o ) were identified, as leaf hydration and functioning of the photosynthetic apparatus under drought are associated with the content of cell wall-bound phenolics (CWPh). Compared with LWC and Ψ o , CWPh fluctuations were more strongly associated with changes in chlorophyll fluorescence. At the vegetative stage, CWPh fluctuations were due to the activity of three loci, of which only QCWPh.4B was also related to changes in F v / F m and ABS/CS m . In the other QTLs (QCWPh.6R.2 and QCWPh.6R.3), the genes of these loci determined also the changes in majority of chlorophyll fluorescence parameters. At the generative stage, the changes in CWPh in loci QCWPh.4B, QCWPh.3R and QCWPh.6R.1 corresponded to those in DI o /CS m . The locus QCWPh.6R.3, active at V stage, controlled majority of chlorophyll fluorescence parameters. This is the first study on mapping quantitative traits in triticale plants exposed to drought at different stages of development, and the first to present the loci for cell wall-bound phenolics.

Acylesterification is one of the common modifications of cell wall non-cellulosic polysaccharides and/or lignin primarily in monocot plants. We analyzed the cell-wall acylesters of black cottonwood (Populus trichocarpa Torr. & Gray) with liquid chromatography-mass spectrometry (LC-MS), Fourier transform-infrared (FT-IR) microspectroscopy, and synchrotron infrared (IR) imaging facility. The results revealed that the cell wall of dicotyledonous poplar, as the walls of many monocot grasses, contains a considerable amount of acylesters, primarily acetyl and p-hydroxycinnamoyl molecules. The “wall-bound” acetate and phenolics display a distinct tissue specific-, bending stress responsible- and developmental-accumulation pattern. The “wall-bound” p-coumarate predominantly accumulated in young leaves and decreased in mature leaves, whereas acetate and ferulate mostly amassed in the cell wall of stems. Along the development of stem, the level of the “wall-bound” ferulate gradually increased, while the basal level of p-coumarate further decreased. Induction of tension wood decreased the accumulation of the “wall-bound” phenolics while the level of acetate remained constant. Synchrotron IR-mediated chemical compositional imaging revealed a close spatial distribution of acylesters with cell wall polysaccharides in poplar stem. These results indicate that different “wall-bound” acylesters play distinct roles in poplar cell wall structural construction and/or metabolism of cell wall matrix components.

The accumulation of soluble and cell wall-bound phenolics in the sugarcane stems of young plants from highly resistant cv. My 5514 and susceptible cv. B 42231, inoculated or not inoculated with smut sporidia, was studied. The ratio of inoculated to uninoculated plants of some cell wall-bound phenolics, such as ferulic, caffeic, and syringic acids increased for the resistant cv. My 5514, whereas it was maintained more or less constantly for the susceptible cv. B 42231. The highest increase of this ratio in the resistant cv. My 5514 corresponded to both caffeic and syringic acids. This could result in a better capacity to cv. My 5514 for an increase in the frequency of bridges between lignin fragments through ester-ether linkages for reinforcing the cell wall and major resistance to the disease. This reinforcement of the cell wall could provide an effective barrier to pathogen entry and spread. Soluble sub-fractions of all phenolics detected showed non-stable patterns. Caffeic acid, that regulates phenylalanine ammonia-lyase activity in sugarcane, showed a significant decrease in its titre at 24 h in the resistant cultivar, principally in the free soluble fraction, whilst the susceptible cultivar enhanced it. We hypothesise that the pathway of hydroxybenzoic acids is only activated once the level of p -coumaric acid justifies the accumulation of hydroxycinnamic acids required for reinforcing the cell wall after inoculation.

Alkaline hydrolysis of cell wall material of tomato hairy roots yielded ferulic acid as the major phenolic compound. Other phenolics were 4-hydroxybenzoic acid, vanillic acid, 4-hydroxybenzaldehyde, vanillin and 4-coumaric acid. The content of phenolics was much higher at the early stage of hairy root growth. The ferulic acid content decreased up to 30 days and then sharply increased to 360 μg/g at 60 days of growth. Elicitation of hairy root cultures with Fusarium mat extract (FME) increased ferulic acid content 4-fold after 24 h. As the pathogen-derived elicitors have specific receptors in plants, FME may thus be used for inducing resistance against Fusarium oxysporum f. sp. lycopersici.

The aim of this work was to identify whether the Ascocalyx abietina culture filtrate has the ability to induce changes in the contents of phenolic substances that might be indicative for the disease response of Norway spruce ( Picea abies ). We focused on the accumulation of soluble and cell wall-bound phenolics, stilbenes as well as extracellular peroxidase activities elicited in the embryogenic cell cultures of Norway spruce by A. abietina culture filtrate. Treatment of spruce cells with fungal culture filtrate (5 and 20% v/v concentrations) evoked an increase in the total contents of phenolic acids (represented by the sum of free, methanol soluble ester- and glycoside-bound phenolics and methanol insoluble cell-wall bound phenolic esters). The challenge with filtrate was in particular manifested in the increase (compared with the control) in the contents of cell wall-bound phenolic acids (by about 100 and 130% in 5 and 20% filtrate, respectively) and soluble phenolic glycosides (by 37 and 65% in 5 and 20% filtrate, respectively) already 6 h after filtrate addition. Significantly decreased concentrations of stilbene glycosides, isorhapontin, astringin and piceid, were determined in filtrate-treated spruce cell cultures 6 and12 h after filtrate addition. The culture filtrate did not influence significantly the extracellular peroxidase activity 12 h after filtrate addition. Reduced extracellular peroxidase activity at 24 and 48 h in treated cells and decline in the amounts of soluble phenolics coincided with the rate of browning of filtrate-treated cells.