Vascular plants appeared ~410 million years ago then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes (1). We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first non-seed vascular plant genome reported. By comparing gene content in evolutionary diverse taxa, we found that the transition from a gametophyte- to sporophyte-dominated life cycle required far fewer new genes than the transition from a non-seed vascular to a flowering plant, while secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in post-transcriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the tasiRNA pathway and extensive RNA editing of organellar genes.

SummaryLignin, a phenolic polymer derived mainly from hydroxycinnamyl alcohols, is ubiquitously present in tracheophytes. The development of lignin biosynthesis has been considered to be one of the key factors that allowed land plants to flourish in terrestrial ecosystems. Lignin provides structural rigidity for tracheophytes to stand upright, and strengthens the cell wall of their water-conducting tracheary elements to withstand the negative pressure generated during transpiration. In this review, we discuss a number of aspects regarding the origin and evolution of lignin biosynthesis during land plant evolution, including the establishment of its monomer biosynthetic scaffold, potential precursors to the lignin polymer, as well as the emergence of the polymerization machinery and regulatory system. The accumulated knowledge on the topic, as summarized here, provides us with an evolutionary view on how this complex metabolic system emerged and developed.

SummaryLignin, a major component of the cell wall of vascular plants, has long been recognized for its negative impact on forage quality, paper manufacturing, and, more recently, cellulosic biofuel production. Over the last two decades, genetic and biochemical analyses of brown midrib mutants of maize, sorghum and related grasses have advanced our understanding of the relationship between lignification and forage digestibility. This work has also inspired genetic engineering efforts aimed at generating crops with altered lignin, with the expectation that these strategies would enhance forage digestibility and/or pulping efficiency. The knowledge gained from these bioengineering efforts has greatly improved our understanding of the optimal lignin characteristics required for various applications of lignocellulosic materials while also contributing to our understanding of the lignin biosynthetic pathway. The recent upswing of interest in cellulosic biofuel production has become the new focus of lignin engineering. Populus trichocarpa and Brachypodium distachyon are emerging as model systems for energy crops. Lignin research on these systems, as well as on a variety of proposed energy crop species, is expected to shed new light on lignin biosynthesis and its regulation in energy crops, and lead to rational genetic engineering approaches to modify lignin for improved biofuel production.

SUMMARYThe initial reactions of the phenylpropanoid pathway convert phenylalanine to p-coumaroyl CoA, a branch point metabolite from which many phenylpropanoids are made. Although the second enzyme of this pathway, cinnamic acid 4-hydroxylase (C4H), is well characterized, a mutant for the gene encoding this enzyme has not yet, to our knowledge, been identified, presumably because knock-out mutations in this gene would have severe phenotypes. This work describes the characterization of an allelic series of Arabidopsis reduced epidermal fluorescence 3 (ref3) mutants, each of which harbor mis-sense mutations in C4H (At2g30490). Heterologous expression of the mutant proteins in Escherichia coli yields enzymes that exhibit P420 spectra, indicative of mis-folded proteins, or have limited ability to bind substrate, indicating that the mutations we have identified affect protein stability and/or enzyme function. In agreement with the early position of C4H in phenylpropanoid metabolism, ref3 mutant plants accumulate decreased levels of several different classes of phenylpropanoid end-products, and exhibit reduced lignin deposition and altered lignin monomer content. Furthermore, these plants accumulate a novel hydroxycinnamic ester, cinnamoylmalate, which is not found in the wild type. The decreased C4H activity in ref3 also causes pleiotropic phenotypes, including dwarfism, male sterility and the development of swellings at branch junctions. Together, these observations indicate that C4H function is critical to the normal biochemistry and development of Arabidopsis.