The evolution of lignin biosynthesis was critical in the transition of plants from an aquatic to an upright terrestrial lifestyle. Lignin is assembled by oxidative polymerization of two major monomers, coniferyl alcohol and sinapyl alcohol. Although two recently discovered laccases, LAC4 and LAC17, have been shown to play a role in lignin polymerization in Arabidopsis thaliana, disruption of both genes only leads to a relatively small change in lignin content and only under continuous illumination. Simultaneous disruption of LAC11 along with LAC4 and LAC17 causes severe plant growth arrest, narrower root diameter, indehiscent anthers, and vascular development arrest with lack of lignification. Genome-wide transcript analysis revealed that all the putative lignin peroxidase genes are expressed at normal levels or even higher in the laccase triple mutant, suggesting that lignin laccase activity is necessary and nonredundant with peroxidase activity for monolignol polymerization during plant vascular development. Interestingly, even though lignin deposition in roots is almost completely abolished in the lac11 lac4 lac17 triple mutant, the Casparian strip, which is lignified through the activity of peroxidase, is still functional. Phylogenetic analysis revealed that lignin laccase genes have no orthologs in lower plant species, suggesting that the monolignol laccase genes diverged after the evolution of seed plants.

Lignin is an aromatic heteropolymer and the second most abundant plant biopolymer after cellulose. It is deposited mostly in the secondary cell walls of vascular plants and is essential for water transport, mechanical support and for plant pathogen defense. Lignin biosynthesis is a highly energy-consuming and irreversible process that responds to many developmental and environmental cues, including light, sugar content, circadian clock, plant hormones and wounding. During the past decade, many transcription factors involved in lignin biosynthesis have been identified and characterized. In this review, we assess how these transcriptional activators and repressors modulate lignin biosynthesis, and discuss crosstalk between the lignin biosynthesis pathway and other physiological processes.

Phenylpropanoids can function as preformed and inducible antimicrobial compounds, as well as signal molecules, in plant-microbe interactions. Since we last reviewed the field 8 years ago, there has been a huge increase in our understanding of the genes of phenylpropanoid biosynthesis and their regulation, brought about largely by advances in genome technology, from whole-genome sequencing to massively parallel gene expression profiling. Here, we present an overview of the biosynthesis and roles of phenylpropanoids in plant defence, together with an analysis of confirmed and predicted phenylpropanoid pathway genes in the sequenced genomes of 11 plant species. Examples are provided of phylogenetic and expression clustering analyses, and the large body of underlying genomic data is provided through a website accessible from the article.

Restructuring is ubiquitous in thermocatalysis and of pivotal importance to identify the real active site, yet it is less explored in electrocatalysis. Herein, by using operando X-ray absorption spectroscopy in conjunction with advanced electron microscopy, we reveal the restructuring of the as-synthesized Cu− N 4 single-atom site to the nanoparticles of ∼5 nm during the electrochemical reduction of nitrate to ammonia, a green ammonia production route upon combined with the plasma-assisted oxidation of nitrogen. The reduction of Cu 2+ to Cu + and Cu 0 and the subsequent aggregation of Cu 0 single atoms is found to occur concurrently with the enhancement of the NH 3 production rate, both of them are driven by the applied potential switching from 0.00 to −1.00 V versus RHE. The maximum production rate of ammonia reaches 4.5 mg cm −2 h −1 (12.5 mol NH 3 g Cu −1 h −1 ) with a Faradaic efficiency of 84.7% at −1.00 V versus RHE, outperforming most of the other Cu catalysts reported previously. After electrolysis, the aggregated Cu nanoparticles are reversibly disintegrated into single atoms and then restored to the Cu−N 4 structure upon being exposed to an ambient atmosphere, which masks the potential-induced restructuring during the reaction. The synchronous changes of the Cu 0 percentage and the ammonia Faradaic efficiency with the applied potential suggests that the Cu nanoparticles are the genuine active sites for nitrate reduction to ammonia, which is corroborated with both the post-deposited Cu NP catalyst and density functional theory calculations.