Rerouting of the lignin biosynthetic pathway by inhibition of cytosolic shikimate recycling in transgenic hybrid aspen

Ectopic Production of 3,4-Dihydroxybenzoate in Planta Affects Cellulose Structure and Organization

Lignocellulosic biomass is a highly sustainable and largely carbon dioxide neutral feedstock for the production of biofuels and advanced biomaterials. Although thermochemical pretreatment is typically used to increase the efficiency of cell wall deconstruction, genetic engineering of the major plant cell wall polymers, especially lignin, has shown promise as an alternative approach to reduce biomass recalcitrance. Poplar trees with reduced lignin content and altered composition were previously developed by overexpressing bacterial 3-dehydroshikimate dehydratase (QsuB) enzyme to divert carbon flux from the shikimate pathway. In this work, three transgenic poplar lines with increasing QsuB expression levels and different lignin contents were studied using small-angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS). SANS showed that although the cellulose microfibril cross-sectional dimension remained unchanged, the ordered organization of the microfibrils progressively decreased with increased QsuB expression. This was correlated with decreasing total lignin content in the QsuB lines. WAXS showed that the crystallite dimensions of cellulose microfibrils transverse to the growth direction were not affected by the QsuB expression, but the crystallite dimensions parallel to the growth direction were decreased by ∼20%. Cellulose crystallinity was also decreased with increased QsuB expression, which could be related to high levels of 3,4-dihydroxybenzoate, the product of QsuB expression, disrupting microfibril crystallization. In addition, the cellulose microfibril orientation angle showed a bimodal distribution at higher QsuB expression levels. Overall, this study provides new structural insights into the impact of ectopic synthesis of small-molecule metabolites on cellulose organization and structure that can be used for future efforts aimed at reducing biomass recalcitrance.

Wood of trees: Cellular structure, molecular formation, and genetic engineering

Wood is an invaluable asset to human society due to its renewable nature, making it suitable for both sustainable energy production and material manufacturing. Additionally, wood derived from forest trees plays a crucial role in sequestering a significant portion of the carbon dioxide fixed during photosynthesis by terrestrial plants. Nevertheless, with the expansion of the global population and ongoing industrialization, forest coverage has been substantially decreased, resulting in significant challenges for wood production and supply. Wood production practices have changed away from natural forests toward plantation forests. Thus, understanding the underlying genetic mechanisms of wood formation is the foundation for developing high-quality, fast-growing plantation trees. Breeding ideal forest trees for wood production using genetic technologies has attracted the interest of many. Tremendous studies have been carried out in recent years on the molecular, genetic, and cell-biological mechanisms of wood formation, and considerable progress and findings have been achieved. These studies and findings indicate enormous possibilities and prospects for tree improvement. This review will outline and assess the cellular and molecular mechanisms of wood formation, as well as studies on genetically improving forest trees, and address future development prospects.

Protein profile analysis of tension wood development in response to artificial bending and gravitational stimuli in Betula platyphylla

Betula platyphylla Suk (birch) is an excellent short-term hardwood species with growth and wood characteristics well suited to wood industries. To investigate the molecular mechanism of wood development in birch, a tension wood (TW) induced system was used to explore the regulatory mechanism at the protein level and identify the key proteins involved in xylem development in birch. The results of dyeing with Safranin O-Fast Green indicated that the cellulose content of TW was significantly higher than that of opposite wood (OW) or normal wood (NW), and the lignin content in TW was significantly lower than that in OW and NW after artificial bending of birch stems. Protein profile analysis of TW, NW and OW by iTRAQ revealed that there were 639 and 460 differentially expressed proteins (DEPs) between TW/OW and TW/NW, respectively. The DEPs were mainly enriched in tyrosine metabolism, glycolysis/gluconeogenesis, phenylalanine and tyrosine metabolism, phenylpropanoid and pyruvate metabolism, the pentose phosphate pathway, the citrate cycle (TCA cycle), fructose and mannose metabolism, carbon fixation in photosynthetic organisms, fatty acid biosynthesis, photosynthesis proteins and other pathways. The proteins in the citrate cycle were upregulated. The expression levels of PGI, PGM and FRK proteins related to cellulose synthesis increased and the expression levels of PAL, 4CL and COMT related to lignin synthesis decreased, leading to an increase in cellulose content and decreased lignin levels in TW. PPI analysis revealed that key DEPs interact with each other, indicating that these proteins form complexes to implement this function, which may provide important insights for wood formation at the molecular level.

Characterization key genes of Arabidopsis seedlings in response to β-caryophyllene, eugenol using combined transcriptome and WGCN analysis

Weeds present a significant challenge to high crop yield and quality. In our study, we investigated the phytotoxic activity of β-caryophyllene (BCP) and eugenol, which are natural allelopathic chemical compounds, on Arabidopsis seedlings. We found that these compounds inhibited the growth of Arabidopsis thaliana plants. When either BCP or eugenol was applied, it led to decrease in the content of cell wall components such as lignin, cellulose, hemicellulose, and pectin; and increase in the levels of endogenous hormones like ETH, ABA, SA, and JA in the seedlings. Through transcriptome profiling, we identified 7181 differentially expressed genes (DEGs) in the roots and shoots that were induced by BCP or eugenol. The genes involved in the synthesis of lignin, cellulose, hemicellulose, and pectin were down-regulated, whereas genes related to synthesis and signal transduction of ABA, ETH, SA, and JA were up-regulated. However, genes related to IAA synthesis and signal transduction were found to be down-regulated. Furthermore, we characterized 24 hub genes using Weighted Correlation Network Analysis (WGCNA). Among them, the identified 16 genes in response to BCP was primarily associated with hypoxia stress, while 8 genes induced by eugenol were linked to inhibition of cell division. Our results suggested that BCP and eugenol had ability to target multiple genes to inhibit growth and development of Arabidopsis plants. Therefore, they can serve as excellent candidates for natural biological herbicides.

Combination of transcriptomics, metabolomics and physiological traits reveals the effects of polystyrene microplastics on photosynthesis, carbon and nitrogen metabolism in cucumber (Cucumis sativus L.)

Although microplastic pollution has been widely studied, the mechanism by which they influence plant photosynthesis and carbon and nitrogen metabolism remains unclear. We aimed to explore the effects of polystyrene microplastics (PS) on photosynthesis and carbon and nitrogen metabolism in cucumber using 5 μm and 0.1 μm PS particles. The PS treatments significantly reduced the stability of cucumber mesophyll cells and photosynthetic parameters and increased the soluble sugar content in cucumber leaves. The 5 μm PS affected the photosynthetic pathway by changing the expression of enzyme genes required for the synthesis of NADPH and ATP, which decreased the photosynthetic capacity in cucumber leaves. However, 0.1 μm PS altered the genes expression of phosphoenolpyruvate carboxykinase (PEPCK) and phosphoenolpyruvate carboxylase (PEPC), which affected the intercellular CO2 concentration and attenuated the negative effects on photosynthetic efficiency. Additionally, PS reduced the expression levels of nitrate/nitrite transporter (NRT) and nitrate reductase (NR), reducing the nitrogen use efficiency in cucumber leaves and mesophyll cells damage through increased accumulation of reduced glutathione (GSH), γ-glutamylcysteine (γ-GC), and citrulline. This study provides a new scientific basis for exploring the effects of microplastics on plant photosynthesis and carbon and nitrogen metabolism.

Lignin engineering in forest trees: From gene discovery to field trials

Wood is an abundant and renewable feedstock for the production of pulp, fuels, and biobased materials. However, wood is recalcitrant toward deconstruction into cellulose and simple sugars, mainly because of the presence of lignin, an aromatic polymer that shields cell-wall polysaccharides. Hence, numerous research efforts have focused on engineering lignin amount and composition to improve wood processability. Here, we focus on results that have been obtained by engineering the lignin biosynthesis and branching pathways in forest trees to reduce cell-wall recalcitrance, including the introduction of exotic lignin monomers. In addition, we draw general conclusions from over 20 years of field trial research with trees engineered to produce less or altered lignin. We discuss possible causes and solutions for the yield penalty that is often associated with lignin engineering in trees. Finally, we discuss how conventional and new breeding strategies can be combined to develop elite clones with desired lignin properties. We conclude this review with priorities for the development of commercially relevant lignin-engineered trees.

Effects of the nitrogen form ratios on photosynthetic productivity of poplar under condition of phenolic acids

Phenolic acids can reduce nitrogen utilization rate of poplar, which seriously restrict the productivity of poplar plantation. In this study, three phenolic acid concentrations (T0, T1, and T2) and three ratios of nitrogen forms (NH₄⁺-N to NO₃^--were 1:3, 1:7, and 1:14) were chosen for orthogonal experiment on poplar (Populus × euramericana "Neva") seedlings to study the effects of the nitrogen form ratios on photosynthetic productivity of poplar under environment of phenolic acids. Results showed that photosynthetic physiology parameters were influenced by both phenolic acid concentration and nitrogen form ratio. The order of net photosynthetic rate (P_N) values obtained from 9 treatments were T1-1:3, T0-1:3, T2-1:3, T0-1:7, T1-1:7, T0-1:14, T2-1:7, T1-1:14, and T2-1:14 (from high to low). Under environment of phenolic acids, when poplar were treated with NH₄⁺-N to NO₃^--N ratio of 1:14, the major limitation factor of photosynthesis was non stomatal factor. When poplar were treated with NH₄⁺-N to NO₃-N ratio of 1:3, the major limitation factor of photosynthesis changed to stomatal factor. The leaf nitrogen content and total biomass were obviously positively related with P_N (p < 0.05). Phenolic acid inhibited photosynthetic productivity of poplar in a major way and this effect decreased with increase of the content of NH₄⁺-N.

Rice Straw Utilisation for Bioenergy Production: A Brief Overview

Unsustainable rice straw management causes environmental impacts; hence, utilisation of rice straw for bioenergy is a promising strategy for sustainable rice straw management. Although rice straw has a high potential for bioenergy generation, the whole production cycle and application may cause environmental damage that is not fully understood. Hence, environmental performance studies are required to determine the most effective rice straw utilisation options. A comprehensive approach, such as life-cycle assessment (LCA), can give comprehensive information on the possible environmental effects of rice straw utilisation for bioenergy. Therefore, this study briefly overviews the LCA of rice straw utilisation for bioenergy production. It is found that utilisation of rice straw for bioenergy could reduce global warming potential compared to energy production from fossil fuels. However, it is suggested that other impact categories in LCA be evaluated in the bioenergy production from rice straw research to determine the overall sustainability of the production.