A Lignin Molecular Brace Controls Precision Processing of Cell Walls Critical for Surface Integrity in Arabidopsis.

The cell wall, a defining feature of plants, provides a rigid structure critical for bonding cells together. To overcome this physical constraint, plants must process cell wall linkages during growth and development. However, little is known about the mechanism guiding cell-cell detachment and cell wall remodeling. Here, we identify two neighboring cell types in Arabidopsis that coordinate their activities to control cell wall processing, thereby ensuring precise abscission to discard organs. One cell type produces a honeycomb structure of lignin, which acts as a mechanical "brace" to localize cell wall breakdown and spatially limit abscising cells. The second cell type undergoes transdifferentiation into epidermal cells, forming protective cuticle, demonstrating de novo specification of epidermal cells, previously thought to be restricted to embryogenesis. Loss of the lignin brace leads to inadequate cuticle formation, resulting in surface barrier defects and susceptible to infection. Together, we show how plants precisely accomplish abscission.

Reassessing the claimed cytokinin-substituting activity of dehydrodiconiferyl alcohol glucoside.

Dehydrodiconiferyl alcohol glucoside (DCG) is a phenylpropanoid-derived plant metabolite with reported cytokinin-substituting and cell-division-promoting activity. Despite its claimed activity, DCG did not trigger morphological changes in Arabidopsis seedlings nor did it alter transcriptional shifts in cell division and cytokinin-responsive genes. In reinvestigating the bioactivity of DCG in its original setting, the previously described stimulation of tobacco callus formation could not be confirmed. No evidence was found that DCG is actually taken up by plant cells, which could explain the absence of any observable activity in the performed experiments. The DCG content in plant tissue increased when feeding explants with the DCG aglycone dehydrodiconiferyl alcohol, which is readily taken up and converted to DCG by plant cells. Despite the increased DCG content, no activity for this metabolite could be demonstrated. Our results therefore demand a reevaluation of the often-quoted cytokinin-substituting and cell-division-promoting activity that has previously been attributed to this metabolite.

Lignin with controlled structural properties by N-heterocycle-based deep eutectic solvent extraction.

The complex and heterogeneous nature of the lignin macromolecule has presented a lasting barrier to its utilization. To achieve high lignin yield, the technical lignin extraction process usually severely modifies and condenses the native structure of lignin, which is a critical drawback for its utilization in conversion processes. In addition, there is no method capable of separating lignin from plant biomass with controlled structural properties. Here, we developed an N-heterocycle-based deep eutectic solvent formed between lactic acid and pyrazole (La-Py DES) with a binary hydrogen bonding functionality resulting in a high affinity toward lignin. Up to 93.7% of lignin was extracted from wheat straw biomass at varying conditions from 90 °C to 145 °C. Through careful selection of treatment conditions as well as lactic acid to pyrazole ratios, lignin with controlled levels of ether linkage content, hydroxyl group content, and average molecular weight can be generated. Under mild extraction conditions (90 °C to 120 °C), light-colored native-like lignin can be produced with up to 80% yield, whereas ether linkage-free lignin with low polydispersity can be obtained at 145 °C. Overall, this study offers a new strategy for native lignin extraction and generating lignin with controlled structural properties.

Isotopic clumping in wood as a proxy for photorespiration in trees.

Photorespiration can limit gross primary productivity in terrestrial plants. The rate of photorespiration relative to carbon fixation increases with temperature and decreases with atmospheric [CO2]. However, the extent to which this rate varies in the environment is unclear. Here, we introduce a proxy for relative photorespiration rate based on the clumped isotopic composition of methoxyl groups (R-O-CH3) in wood. Most methoxyl C-H bonds are formed either during photorespiration or the Calvin cycle and thus their isotopic composition may be sensitive to the mixing ratio of these pathways. In water-replete growing conditions, we find that the abundance of the clumped isotopologue 13CH2D correlates with temperature (18-28 °C) and atmospheric [CO2] (280-1000 ppm), consistent with a common dependence on relative photorespiration rate. When applied to a global dataset of wood, we observe global trends of isotopic clumping with climate and water availability. Clumped isotopic compositions are similar across environments with temperatures below ~18 °C. Above ~18 °C, clumped isotopic compositions in water-limited and water-replete trees increasingly diverge. We propose that trees from hotter climates photorespire substantially more than trees from cooler climates. How increased photorespiration is managed depends on water availability: water-replete trees export more photorespiratory metabolites to lignin whereas water-limited trees either export fewer overall or direct more to other sinks that mitigate water stress. These disparate trends indicate contrasting responses of photorespiration rate (and thus gross primary productivity) to a future high-[CO2] world. This work enables reconstructing photorespiration rates in the geologic past using fossil wood.

Biochemical and structural characterization of a sphingomonad diarylpropane lyase for cofactorless deformylation.

Lignin valorization is being intensely pursued via tandem catalytic depolymerization and biological funneling to produce single products. In many lignin depolymerization processes, aromatic dimers and oligomers linked by carbon-carbon bonds remain intact, necessitating the development of enzymes capable of cleaving these compounds to monomers. Recently, the catabolism of erythro-1,2-diguaiacylpropane-1,3-diol (erythro-DGPD), a ring-opened lignin-derived ß-1 dimer, was reported in Novosphingobium aromaticivorans. The first enzyme in this pathway, LdpA (formerly LsdE), is a member of the nuclear transport factor 2 (NTF-2)-like structural superfamily that converts erythro-DGPD to lignostilbene through a heretofore unknown mechanism. In this study, we performed biochemical, structural, and mechanistic characterization of the N. aromaticivorans LdpA and another homolog identified in Sphingobium sp. SYK-6, for which activity was confirmed in vivo. For both enzymes, we first demonstrated that formaldehyde is the C1 reaction product, and we further demonstrated that both enantiomers of erythro-DGPD were transformed simultaneously, suggesting that LdpA, while diastereomerically specific, lacks enantioselectivity. We also show that LdpA is subject to a severe competitive product inhibition by lignostilbene. Three-dimensional structures of LdpA were determined using X-ray crystallography, including substrate-bound complexes, revealing several residues that were shown to be catalytically essential. We used density functional theory to validate a proposed mechanism that proceeds via dehydroxylation and formation of a quinone methide intermediate that serves as an electron sink for the ensuing deformylation. Overall, this study expands the range of chemistry catalyzed by the NTF-2-like protein family to a prevalent lignin dimer through a cofactorless deformylation reaction.

Characterization of a cytochrome P450 that catalyzes the O-demethylation of lignin-derived benzoates.

Cytochromes P450 (P450s) are a superfamily of heme-containing enzymes possessing a broad range of monooxygenase activities. One such activity is O-demethylation, an essential and rate-determining step in emerging strategies to valorize lignin that employ carbon-carbon bond cleavage. We recently identified PbdA, a P450 from Rhodococcus jostii RHA1, and PbdB, its cognate reductase, which catalyze the O-demethylation of para-methoxylated benzoates (p-MBAs) to initiate growth of RHA1 on these compounds. PbdA had the highest affinity (Kd = 3.8 ± 0.6 µM) and apparent specificity (kcat/KM = 20,000 ± 3000 M-1 s-1) for p-MBA. The enzyme also O-demethylated two related lignin-derived aromatic compounds with remarkable efficiency: veratrate and isovanillate. PbdA also catalyzed the hydroxylation and dehydrogenation of p-ethylbenzoate even though RHA1 did not grow on this compound. Atomic-resolution structures of PbdA in complex with p-MBA, p-ethylbenzoate, and veratrate revealed a cluster of three residues that form hydrogen bonds with the substrates' carboxylate: Ser87, Ser237, and Arg84. Substitution of these residues resulted in lower affinity and O-demethylation activity on p-MBA as well as increased affinity for the acetyl analog, p-methoxyacetophenone. The S87A and S237A variants of PbdA also catalyzed the O-demethylation of an aldehyde analog of p-MBA, p-methoxy-benzaldehyde, while the R84M variant did not, despite binding this compound with high affinity. These results suggest that Ser87, Ser237, and Arg84 are not only important determinants of specificity but also help to orientate that substrate correctly in the active site. This study facilitates the design of biocatalysts for lignin valorization.

Characterization of lignin-degrading enzyme PmdC, which catalyzes a key step in the synthesis of polymer precursor 2-pyrone-4,6-dicarboxylic acid.

Pyrone-2,4-dicarboxylic acid (PDC) is a valuable polymer precursor that can be derived from the microbial degradation of lignin. The key enzyme in the microbial production of PDC is 4-carboxy-2-hydroxymuconate-6-semialdehyde (CHMS) dehydrogenase, which acts on the substrate CHMS. We present the crystal structure of CHMS dehydrogenase (PmdC from Comamonas testosteroni) bound to the cofactor NADP, shedding light on its three-dimensional architecture, and revealing residues responsible for binding NADP. Using a combination of structural homology, molecular docking, and quantum chemistry calculations, we have predicted the binding site of CHMS. Key histidine residues in a conserved sequence are identified as crucial for binding the hydroxyl group of CHMS and facilitating dehydrogenation with NADP. Mutating these histidine residues results in a loss of enzyme activity, leading to a proposed model for the enzyme's mechanism. These findings are expected to help guide efforts in protein and metabolic engineering to enhance PDC yields in biological routes to polymer feedstock synthesis.

Sweetpotato sucrose transporter IbSUT1 alters storage roots formation by regulating sucrose transport and lignin biosynthesis.

The formation and development of storage roots is the most important physiological process in sweetpotato production. Sucrose transporters (SUTs) regulate sucrose transport from source to sink organs and play important roles in growth and development of plants. However, whether SUTs involved in sweetpotato storage roots formation is so far unknown. In this study, we show that IbSUT1, a SUT, is localized to the plasma membrane. Overexpression of IbSUT1 in sweetpotato promotes the sucrose efflux rate from leaves, leading to increased sucrose levels in roots, thus induces lignin deposition in the stele, which inhibits the storage roots formation and compromises the yield. Heterologous expression of IbSUT1 in Arabidopsis significantly increases the sucrose accumulation and promotes lignification in the inflorescence stems. RNA-seq and biochemical analysis further demonstrated that IbMYB1 negatively regulates the expression of IbSUT1. Overexpression of IbMYB1 in Arabidopsis reduces the sucrose accumulation and lignification degree in the inflorescence stems. Moreover, co-overexpression of IbMYB1 and IbSUT1 restores the phenotype of lignin over-deposition in Arabidopsis. Collectively, our results reveal that IbSUT1 regulates source-sink sucrose transport and participates in the formation of sweetpotato storage roots and highlight the potential application of IbSUT1 in improving sweetpotato yield in the future.

Overexpression of FERONIA receptor kinase MdMRLK2 regulates lignin accumulation and enhances water use efficiency in apple under long-term water deficit condition.

Water use efficiency (WUE) is crucial for apple tree fitness and survival, especially in response to climatic changes. The receptor-like kinase FERONIA is reportedly an essential regulator of plant stress responses, but its role in regulating WUE under water deficit conditions is unclear. Here, we found that overexpressing the apple FERONIA receptor kinase gene, MdMRLK2, enhanced apple WUE under long-term water deficit conditions. Under drought treatment, 35S::MdMRLK2 apple plants exhibited higher photosynthetic capacity and antioxidant enzyme activities than wild-type (WT) plants. 35S::MdMRLK2 apple plants also showed increased biomass accumulation, root activity, and water potential compared to WT plants. Moreover, MdMRLK2 physically interacts with and phosphorylates cinnamoyl-CoA reductase 1, MdCCR1, an enzyme essential for lignin synthesis, at position Ser260. This interaction likely contributed to increased vessel density, vascular cylinder area, and lignin content in 35S::MdMRLK2 apple plants under drought conditions. Therefore, our findings reveal a novel function of MdMRLK2 in regulating apple WUE under water deficit conditions.

CsPAT1, a GRAS transcription factor, promotes lignin accumulation by antagonistic interacting with CsWRKY13 in tea plants.

Lignin is an important component of plant cell walls and plays crucial roles in the essential agronomic traits of tea quality and tenderness. However, the molecular mechanisms underlying the regulation of lignin biosynthesis in tea plants remain unclear. CsWRKY13 acts as a negative regulator of lignin biosynthesis in tea plants. In this study, we identified a GRAS transcription factor, phytochrome A signal transduction 1 (CsPAT1), that interacts with CsWRKY13. Silencing CsPAT1 expression in tea plants and heterologous overexpression in Arabidopsis demonstrated that CsPAT1 positively regulates lignin accumulation. Further investigation revealed that CsWRKY13 directly binds to the promoters of CsPAL and CsC4H and suppresses transcription of CsPAL and CsC4H. CsPAT1 indirectly affects the promoter activities of CsPAL and CsC4H by interacting with CsWRKY13, thereby facilitating lignin biosynthesis in tea plants. Compared with the expression of CsWRKY13 alone, the co-expression of CsPAT1 and CsWRKY13 in Oryza sativa significantly increased lignin biosynthesis. Conversely, compared with the expression of CsPAT1 alone, the co-expression of CsPAT1 and CsWRKY13 in O. sativa significantly reduced lignin accumulation. These results demonstrated the antagonistic regulation of the lignin biosynthesis pathway by CsPAT1 and CsWRKY13. These findings improve our understanding of lignin biosynthesis mechanisms in tea plants and provide insights into the role of the GRAS transcription factor family in lignin accumulation.

Evolution of sea-surfing plant propagule as revealed by the genomes of Heritiera mangroves.

Coastal forests, such as mangroves, protect much of the tropical and subtropical coasts. Long-distance dispersal via sea-surfing propagules is essential for coastal plants, but the genomic and molecular basis of sea-surfing plant propagule evolution remains unclear. Heritiera fomes and Heritiera littoralis are two coastal plants with typical buoyant fruits. We de novo sequenced and assembled their high-quality genomes. Our phylogenomic analysis indicates H. littoralis and H. fomes originated (at ~6.08 Mya) just before the start of Quaternary sea-level fluctuations. Whole-genome duplication occurred earlier, permitting gene copy gains in the two species. Many of the expanded gene families are involved in lignin and flavonoid biosynthesis, likely contributing to buoyant fruit emergence. It is repeatedly revealed that one duplicated copy to be under positive selection while the other is not. By examining H. littoralis fruits at three different developmental stages, we found that gene expression levels remain stable from young to intermediate. However, ~1000 genes are up-regulated and ~ 3000 genes are down-regulated as moving to mature. Particularly in fruit epicarps, the upregulation of WRKY12 and E2Fc likely constrains the production of p-Coumaroyl-CoA, the key internal substrate for lignin biosynthesis. Hence, to increase fruit impermeability, methylated lignin biosynthesis is shut down by down-regulating the genes CCoAOMT, F5H, COMT, and CSE, while unmethylated lignins are preferentially produced by upregulating CAD and CCR. Similarly, cutin polymers and cuticular waxes accumulate with high levels before maturation in epicarps. Overall, our genome assemblies and analyses uncovered the genomic evolution and temporal transcriptional regulation of sea-surfing propagule.

Anther development in Arabidopsis thaliana involves symplastic isolation and apoplastic gating of the tapetum-middle layer interface.

During flowering plant reproduction, anthers produce pollen grains, the development of which is supported by the tapetum, a nourishing maternal tissue that also contributes non-cell-autonomously to the pollen wall, the resistant external layer on the pollen surface. How the anther restricts movement of the tapetum-derived pollen wall components, while allowing metabolites such as sugars and amino acids to reach the developing pollen, remains unknown. Here, we show experimentally that in arabidopsis thaliana the tapetum and developing pollen are symplastically isolated from each other, and from other sporophytic tissues, from meiosis onwards. We show that the peritapetal strip, an apoplastic structure, separates the tapetum and the pollen grains from other anther cell layers and can prevent the apoplastic diffusion of fluorescent proteins, again from meiosis onwards. The formation and selective barrier functions of the peritapetal strip require two NADPH oxidases, RBOHE and RBOHC, which play a key role in pollen formation. Our results suggest that, together with symplastic isolation, gating of the apoplast around the tapetum may help generate metabolically distinct anther compartments.

Characterization of the degradation products of lignocellulosic biomass by using tandem mass spectrometry experiments, model compounds, and quantum chemical calculations.

Biomass-derived degraded lignin and cellulose serve as possible alternatives to fossil fuels for energy and chemical resources. Fast pyrolysis of lignocellulosic biomass generates bio-oil that needs further refinement. However, as pyrolysis causes massive degradation to lignin and cellulose, this process produces very complex mixtures. The same applies to degradation methods other than fast pyrolysis. The ability to identify the degradation products of lignocellulosic biomass is of great importance to be able to optimize methodologies for the conversion of these mixtures to transportation fuels and valuable chemicals. Studies utilizing tandem mass spectrometry have provided invaluable, molecular-level information regarding the identities of compounds in degraded biomass. This review focuses on the molecular-level characterization of fast pyrolysis and other degradation products of lignin and cellulose via tandem mass spectrometry based on collision-activated dissociation (CAD). Many studies discussed here used model compounds to better understand both the ionization chemistry of the degradation products of lignin and cellulose and their ions' CAD reactions in mass spectrometers to develop methods for the structural characterization of the degradation products of lignocellulosic biomass. Further, model compound studies were also carried out to delineate the mechanisms of the fast pyrolysis reactions of lignocellulosic biomass. The above knowledge was used to assign likely structures to many degradation products of lignocellulosic biomass.

A hierarchical ubiquitination-mediated regulatory module controls bamboo lignin biosynthesis.

The lignocellulosic feedstock of woody bamboo shows promising potential as an alternative to conventional wood, attributed to its excellent properties. The content and distribution of lignin serve as the foundation of these properties. While the regulation of lignin biosynthesis in bamboo has been extensively studied at the transcriptional level, its posttranslational control has remained poorly understood. This study provides a ubiquitinome dataset for moso bamboo (Phyllostachys edulis), identifying 13015 ubiquitinated sites in 4849 unique proteins. We further identified Kelch repeat F-boxprotein 9 (PeKFB9) that plays a negative role in lignin biosynthesis. Heterologous expression of PeKFB9 resulted in reduced accumulation of lignin and decreased phenylalanine ammonia-lyase (PAL) activities. Both in vitro and in vivo assays identified interaction between PeKFB9 and PePAL10. Further examination revealed that SCFPeKFB9 mediated the ubiquitination and degradation of PePAL10 via the 26S proteasome pathway. Moreover, PebZIP28667 could bind to the PePAL10 promoter to significantly inhibit its transcription, and ubiquitination of PebZIP28667 weakened this inhibition. Collectively, our findings reveal a PeKFB9-PePAL10/PebZIP28667-PePAL10 module that acts as a negative regulator of lignin biosynthesis. This study advances our understanding of posttranslational regulation in plant lignification, which will facilitate the improvement of the properties of bamboo wood and the breeding of varieties.

Histone deacetylase GhHDA5 negatively regulates Verticillium wilt resistance in cotton.

Verticillium wilt (VW) caused by Verticillium dahliae (V. dahliae) is one of the most destructive diseases in cotton (Gossypium spp.). Histone acetylation plays critical roles in plant development and adaptive responses to biotic and abiotic stresses. However, the relevance of histone acetylation in cotton VW resistance remains largely unclear. Here, we identified Histone Deacetylase 5 (GhHDA5) from upland cotton (Gossypium hirsutum L.), as a negative regulator of VW resistance. GhHDA5 expression was responsive to V. dahliae infection. Silencing GhHDA5 in upland cotton led to improved resistance to V. dahliae, while heterologous expression of GhHDA5 in Arabidopsis (Arabidopsis thaliana) compromised V. dahliae tolerance. GhHDA5 repressed the expression of several lignin biosynthesis-related genes, such as 4-coumarate: CoA ligase gene Gh4CL3 and ferulate 5-hydroxylase gene GhF5H, through reducing the acetylation level of Histone H3 Lysine 9 and 14 (H3K9K14ac) at their promoter regions, thereby resulting in an increased deposition of lignin, especially S monomers, in the GhHDA5-silenced cotton plants. The silencing of GhF5H impaired cotton VW tolerance. Additionally, the silencing of GhHDA5 also promoted the production of reactive oxygen species (ROS), elevated the expression of several pathogenesis-related genes (PRs), and altered the content and signaling of the phytohormones salicylic acid (SA), jasmonic acid (JA) and strigolactones (SLs) after V. dahliae infection. Taken together, our findings suggest that GhHDA5 negatively regulates cotton VW resistance through modulating disease-induced lignification and the ROS- and phytohormone-mediated defense response.

MYB168 and WRKY20 transcription factors synergistically regulate lignin monomer synthesis during potato tuber wound healing.

Lignin is a critical component of the closing layer of the potato (Solanum tuberosum L.) tuber during healing; however, the molecular mechanism of its formation remains poorly understood. To elucidate the molecular mechanism of tuber healing, we screened the genes encoding transcription factors that regulate lignin synthesis(StMYB24/49/105/144/168, StWRKY19/20/22/23/34) and the key genes involved in lignin monomer synthesis (PHENYLALANINE AMMONIA LYASE 5 (StPAL5) and CINNAMYL ALCOHOL DEHYDROGENASE 14 (StCAD14)) for induced expression after wounding using transcriptome data. DLR, Y1H, EMSA, and ChIP-qPCR assays revealed that StMYB168 could bind directly to the StPAL5 and StCAD14 promoters to activate their expression and that StWRKY20 enhanced this regulation with a synergistic effect. Y2H, BiFC, and Co-IP assays showed that StMYB168 interacted with StWRKY20 to form a MYB-WRKY complex. Furthermore, transient overexpression of StMYB168 and StWRKY20 in Nicotiana benthamiana leaves upregulated the expression of NbPAL and NbCAD10 and promoted lignin accumulation in the leaves. In addition, overexpression of StWRKY20 and StMYB168 together resulted in higher expression levels of NbPAL and NbCAD10 and higher levels of lignin monomer and total lignin. In contrast, silencing of StMYB168 and StWRKY20 in potato significantly reduced the lignin content of wounded tubers. In conclusion, StMYB168 and StWRKY20 are important regulators of lignin biosynthesis in potato tubers during healing and can positively regulate lignin biosynthesis by forming a complex. The elucidation of this regulatory module provides information on the regulatory mechanism of lignin monomer synthesis in wounded tubers at the transcriptional level.

Leaf Gas Film 1 promotes glycerol ester accumulation and formation of a tight root barrier to radial O2 loss in rice.

Rice (Oryza sativa L.) and many other wetland plants form an apoplastic barrier in the outer parts of the roots to restrict radial O2 loss to the rhizosphere during soil flooding. This barrier facilitates longitudinal internal O2 diffusion via gas-filled tissues from shoot to root apices, enabling root growth in anoxic soils. We tested the hypothesis that Leaf Gas Film 1 (LGF1), which influences leaf hydrophobicity in rice, plays a crucial role in tight outer apoplastic barriers formation in rice roots. We examined the roots of a rice mutant (dripping wet leaf 7, drp7) lacking functional LGF1, its wild type, and an LGF1 overexpression line for their capacity to develop outer apoplastic barriers that restrict radial O2 loss. We quantified the chemical composition of the outer part of the root and measured radial O2 diffusion from intact roots. The drp7 mutant exhibited a weak barrier to radial O2 loss compared to the wild type. However, introducing functional LGF1 into the mutant fully restored tight barrier function. The formation of a tight barrier to radial O2 loss was associated with increased glycerol ester levels in exodermal cells, rather than differences in total root suberization or lignification. These results demonstrate that, in addition to its role in leaf hydrophobicity regulation, LGF1 plays an important role in controlling the function of the outer apoplastic barriers in roots. Our study suggests that increased deposition of glycerol esters in the suberized root exodermis establishes a tight barrier to radial O2 loss in rice roots.

A glutathione S-transferase regulates lignin biosynthesis and enhances salt tolerance in tomato.

Salt stress adversely affects the growth and yield of crops. Glutathione S-transferases (GSTs) are involved in plant growth and responses to biotic and abiotic stresses. In this study, 400 mM NaCl stress significantly induced the expression of Glutathione S-transferase U43 (SlGSTU43) in the roots of the wild-type tomato (Solanum lycopersicum L.) plants. Overexpressing SlGSTU43 enhanced the ability of scavenging reactive oxygen species (ROS) in tomato leaves and roots under NaCl stress, while SlGSTU43 knock-out mutants showed the opposite performance. RNA sequencing analysis revealed that overexpressing SlGSTU43 affected the expression of genes related to lignin biosynthesis. We demonstrated that SlGSTU43 can regulate the lignin content in tomato through its interaction with SlCOMT2, a key enzyme involved in lignin biosynthesis, and promote the growth of tomato plants under NaCl stress. In addition, SlMYB71 and SlWRKY8 interact each other, and can directly bind to the promoter of SlGSTU43 to transcriptionally activate its expression separately or in combination. When SlMYB71 and SlWRKY8 were silenced in tomato plants individually or collectively, the plants were sensitive to NaCl stress, and their GST activities and lignin contents decreased. Our research indicates that SlGSTU43 can enhance salt stress tolerance in tomato by regulating lignin biosynthesis, which is regulated by interacting with SlCOMT2, as well as SlMYB71 and SlWRKY8. This finding broadens our understanding of GST functions.

Bacterial catabolism of acetovanillone, a lignin-derived compound.

Bacterial catabolic pathways have considerable potential as industrial biocatalysts for the valorization of lignin, a major component of plant-derived biomass. Here, we describe a pathway responsible for the catabolism of acetovanillone, a major component of several industrial lignin streams. Rhodococcus rhodochrous GD02 was previously isolated for growth on acetovanillone. A high-quality genome sequence of GD02 was generated. Transcriptomic analyses revealed a cluster of eight genes up-regulated during growth on acetovanillone and 4-hydroxyacetophenone, as well as a two-gene cluster up-regulated during growth on acetophenone. Bioinformatic analyses predicted that the hydroxyphenylethanone (Hpe) pathway proceeds via phosphorylation and carboxylation, before ß-elimination yields vanillate from acetovanillone or 4-hydroxybenzoate from 4-hydroxyacetophenone. Consistent with this prediction, the kinase, HpeHI, phosphorylated acetovanillone and 4-hydroxyacetophenone. Furthermore, HpeCBA, a biotin-dependent enzyme, catalyzed the ATP-dependent carboxylation of 4-phospho-acetovanillone but not acetovanillone. The carboxylase's specificity for 4-phospho-acetophenone (kcat/KM = 34 ± 2 mM-1 s-1) was approximately an order of magnitude higher than for 4-phospho-acetovanillone. HpeD catalyzed the efficient dephosphorylation of the carboxylated products. GD02 grew on a preparation of pine lignin produced by oxidative catalytic fractionation, depleting all of the acetovanillone, vanillin, and vanillate. Genomic and metagenomic searches indicated that the Hpe pathway occurs in a relatively small number of bacteria. This study facilitates the design of bacterial strains for biocatalytic applications by identifying a pathway for the degradation of acetovanillone.

Explosive seed dispersal depends on SPL7 to ensure sufficient copper for localized lignin deposition via laccases.

Exploding seed pods evolved in the Arabidopsis relative Cardamine hirsuta via morphomechanical innovations that allow the storage and rapid release of elastic energy. Asymmetric lignin deposition within endocarpb cell walls is one such innovation that is required for explosive seed dispersal and evolved in association with the trait. However, the genetic control of this novel lignin pattern is unknown. Here, we identify three lignin-polymerizing laccases, LAC4, 11, and 17, that precisely colocalize with, and are redundantly required for, asymmetric lignification of endocarpb cells. By screening for C. hirsuta mutants with less lignified fruit valves, we found that loss of function of the transcription factor gene SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 7 (SPL7) caused a reduction in endocarpb cell-wall lignification and a consequent reduction in seed dispersal range. SPL7 is a conserved regulator of copper homeostasis and is both necessary and sufficient for copper to accumulate in the fruit. Laccases are copper-requiring enzymes. We discovered that laccase activity in endocarpb cell walls depends on the SPL7 pathway to acclimate to copper deficiency and provide sufficient copper for lignin polymerization. Hence, SPL7 links mineral nutrition to efficient dispersal of the next generation.