No abstract

The freeze thaw transfection procedure of Dityatkin et al. (1972) was adapted for the transfection and transformation of A. tumefaciens. Transfection of the strains B6S3 and B6-6 with DNA of the temperate phage PS8cc186 yielded a maximum frequency of 2 10(-7) transfectants per total recipient population. In transformation of the strain GV3100 with the P type plasmid RP4 a maximum frequency of 3.5 10(-7) transformants per total recipient population was obtained. Agrobacterium Ti-plasmids were introduced in the strain GV3100 with a maximal efficiency of 4.5 10(-8). These experiments provide further evidence that the Ti-plasmid is responsible for the oncogenic properties of A tumefaciens and for its capacity to induce "opine" synthesis in Crown-gall plant cells.

The first enzyme of the phenylpropanoid pathway, Phe ammonia-lyase (PAL), is encoded by four genes in Arabidopsis thaliana. Whereas PAL function is well established in various plants, an insight into the functional significance of individual gene family members is lacking. We show that in the absence of clear phenotypic alterations in the Arabidopsis pal1 and pal2 single mutants and with limited phenotypic alterations in the pal1 pal2 double mutant, significant modifications occur in the transcriptome and metabolome of the pal mutants. The disruption of PAL led to transcriptomic adaptation of components of the phenylpropanoid biosynthesis, carbohydrate metabolism, and amino acid metabolism, revealing complex interactions at the level of gene expression between these pathways. Corresponding biochemical changes included a decrease in the three major flavonol glycosides, glycosylated vanillic acid, scopolin, and two novel feruloyl malates coupled to coniferyl alcohol. Moreover, Phe overaccumulated in the double mutant, and the levels of many other amino acids were significantly imbalanced. The lignin content was significantly reduced, and the syringyl/guaiacyl ratio of lignin monomers had increased. Together, from the molecular phenotype, common and specific functions of PAL1 and PAL2 are delineated, and PAL1 is qualified as being more important for the generation of phenylpropanoids.

Cinnamoyl-CoA reductase (CCR) catalyzes the penultimate step in monolignol biosynthesis. We show that downregulation of CCR in transgenic poplar (Populus tremula 3 Populus alba) was associated with up to 50% reduced lignin content and an orange-brown, often patchy, coloration of the outer xylem. Thioacidolysis, nuclear magnetic resonance (NMR), immunocytochemistry of lignin epitopes, and oligolignol profiling indicated that lignin was relatively more reduced in syringyl than in guaiacyl units. The cohesion of the walls was affected, particularly at sites that are generally richer in syringyl units in wild-type poplar. Ferulic acid was incorporated into the lignin via ether bonds, as evidenced independently by thioacidolysis and by NMR. A synthetic lignin incorporating ferulic acid had a red-brown coloration, suggesting that the xylem coloration was due to the presence of ferulic acid during lignification. Elevated ferulic acid levels were also observed in the form of esters. Transcript and metabolite profiling were used as comprehensive phenotyping tools to investigate how CCR downregulation impacted metabolism and the biosynthesis of other cell wall polymers. Both methods suggested reduced biosynthesis and increased breakdown or remodeling of noncellulosic cell wall polymers, which was further supported by Fourier transform infrared spectroscopy and wet chemistry analysis. The reduced levels of lignin and hemicellulose were associated with an increased proportion of cellulose. Furthermore, the transcript and metabolite profiling data pointed toward a stress response induced by the altered cell wall structure. Finally, chemical pulping of wood derived from 5-year-old, field-grown transgenic lines revealed improved pulping characteristics, but growth was affected in all transgenic lines tested.

The ensemble of all phenolics for which the biosynthesis is coregulated with lignin biosynthesis, i.e., metabolites from the general phenylpropanoid, monolignol, and (neo)-lignan biosynthetic pathways and their derivatives, as well as the lignin oligomers, is coined the lignome. In lignifying tissues, the lignome comprises a significant portion of the metabolome. However, as is true for metabolomics in general, the structural elucidation of unknowns represents the biggest challenge in characterizing the lignome. To minimize the necessity to purify unknowns for NMR analysis, it would be desirable to be able to extract structural information from liquid chromatography-mass spectrometry data directly. However, mass spectral libraries for metabolomics are scarce, and no libraries exist for the lignome. Therefore, elucidating the gas-phase fragmentation behavior of the major bonding types encountered in lignome-associated molecules would considerably advance the systematic characterization of the lignome. By comparative MS n analysis of a series of molecules belonging to the -aryl ether, benzodioxane, phenylcoumaran, and resinol groups, we succeeded in annotating typical fragmentations for each of these bonding structures as well as fragmentations that enabled the identification of the aromatic units involved in each bonding structure. Consequently, this work lays the foundation for a detailed characterization of the lignome in different plant species, mutants, and transgenics and for the MS-based sequencing of lignin oligomers and (neo)lignans.Lignin is an aromatic heteropolymer that is mainly present in secondary-thickened plant cell walls where it provides the necessary strength and hydrophobicity for plants to grow in an upward direction and to enable the transport of water, nutrients, and photoassimilates. Lignin is mainly composed of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units derived from the combinatorial coupling of p-coumaryl, coniferyl, and sinapyl alcohols ( Figure 1A), 1 the so-called monolignols that are produced by the general phenylpropanoid and monolignol biosynthetic pathways. [2][3][4][5] Following oxidation by peroxidase and/or laccase, the resulting electron-delocalized monolignol radical has unpaired electron density at its 1-, 3-, O-4-, 5-, and 8-positions ( Figure 1B). As radical coupling at the 8-position is favored, coupling with another monolignol radical results in, after rearomatization, a mixture of dehydrodimers with 8-8′, 8-5′, and 8-O-4′ linkages ( Figure 1C).In addition to these major monomers, several other monomers have been identified in particular species or in plants with modified lignin biosynthesis, 1,3 such as 5-hydroxyconiferyl alcohol in caffeic acid O-methyltransferase (COMT) downregulated transgenic plants, 6,7 dihydroconiferyl alcohol in cinnamyl alcohol dehydrogenase (CAD) deficient loblolly pine, 8 acylated monolignols, such as sinapyl p-hydroxybenzoate in poplar, 9 and hydroxycinnamic acid or hydroxycinnamate esters, such as feruloyl tyramine in tobacco....

Rhodococcus fascians is a nocardiform bacteria that induces leafy galls (fasciation) on dicotyledonous and several monocotyledonous plants. The wild‐type strain D188 contained a conjugative, 200 kb linear extrachromosomal element, pFiD188. Linear plasmid‐cured strains were avirulent and reintroduction of this linear element restored virulence. Pulsed field electrophoresis indicated that the chromosome might also be a linear molecule of 4 megabases. Three loci involved in phytopathogenicity have been identified by insertion mutagenesis of this Fi plasmid. Inactivation of the fas locus resulted in avirulent strains, whereas insertions in the two other loci affected the degree of virulence, yielding attenuated (att) and hypervirulent (hyp) bacteria. One of the genes within the fas locus encoded an isopentenyltranferase (IPT) with low homology to analogous proteins from Gram‐negative phytopathogenic bacteria. IPT activity was detected after expression of this protein in Escherichia coli cells. In R.fascians, ipt expression could only be detected in bacteria induced with extracts from fasciated tissue. R.fascians strains without the linear plasmid but containing this fas locus alone could not provoke any phenotype on plants, indicating additional genes from the linear plasmid were also essential for virulence. These studies, the first genetic analysis of the interaction of a Gram‐positive bacterium with plants, suggest that a novel mechanism for plant tumour induction has evolved in R.fascians independently from the other branches of the eubacteria.

Although the primary structure of proteins, nucleic acids, and carbohydrates can be readily determined, no sequencing method has been described yet for the second most abundant biopolymer on earth (i.e. lignin). Within secondary-thickened plant cell walls, lignin forms an aromatic mesh arising from the combinatorial radical-radical coupling of monolignols and many other less abundant monomers. This polymerization process leads to a plethora of units and linkage types that affect the physicochemical characteristics of the cell wall. Current methods to analyze the lignin structure focus only on the frequency of the major monomeric units and interunit linkage types but do not provide information on the presence of less abundant unknown units and linkage types, nor on how linkages affect the formation of neighboring linkages. Such information can only be obtained using a sequencing approach. Here, we describe, to our knowledge for the first time, a sequencing strategy for lignin oligomers using mass spectrometry. This strategy was then evaluated on the oligomers extracted from wild-type poplar (Populus tremula 3 Populus tremuloides) xylem. In total, 134 lignin trimers to hexamers were observed, of which 36 could be completely sequenced. Interestingly, based on molecular mass data of the unknown monomeric and dimeric substructures, at least 10 unknown monomeric units or interunit linkage types were observed, one of which was identified as an arylglycerol end unit.Lignin is an aromatic heteropolymer that is mainly present in secondary-thickened plant cell walls, allowing the transport of water and nutrients and providing the necessary strength for the plant to grow upwardly Vanholme et al., 2008Vanholme et al., , 2010. In angiosperms, lignin is predominantly composed of guaiacyl (G) and syringyl (S) units that are derived from combinatorial radical-radical coupling of the monolignols coniferyl and sinapyl alcohol, respectively Fig. 1A). Following oxidation of the monolignols by peroxidase and/or laccase, the resulting electron-delocalized radical has unpaired electron density at its 1-, 3-, O-4-, 5-, and 8-positions (Fig. 1B); note that much of the lignin literature uses Greek letters for the side chain, a, b, and g for the 7-, 8-, and 9-positions. As radical coupling at the 8-position is favored, coupling with another monolignol radical affords, after rearomatization, a mixture of dehydrodimers with 8-8-, 8-5-, and 8-O-4-linkages (Fig. 1C). Following dimerization, polymerization will continue by the coupling of the 8-position of an incoming monolignol radical to the O-4-position of the dimer's phenolic end. In the case of a G dimer, coupling can also occur, albeit at a lower frequency, to the 5-position. Thus, chain elongation creates 8-5-and 8-O-4-linkages (Adler, 1977). Besides the monolignols and other monomers that are present in minor amounts , the plasticity of lignin polymerization permits the incorporation of any phenolic that enters the lignification site, subject to its chemical cross-coupling propensit...

Lignin is an aromatic heteropolymer, abundantly present in the walls of secondary thickened cells. Although much research has been devoted to the structure and composition of the polymer to obtain insight into lignin polymerization, the lowmolecular weight oligolignol fraction has escaped a detailed characterization. This fraction, in contrast to the rather inaccessible polymer, is a simple and accessible model that reveals details about the coupling of monolignols, an issue that has raised considerable controversy over the past years. We have profiled the methanol-soluble oligolignol fraction of poplar (Populus spp.) xylem, a tissue with extensive lignification. Using liquid chromatography-mass spectrometry, chemical synthesis, and nuclear magnetic resonance, we have elucidated the structures of 38 compounds, most of which were dimers, trimers, and tetramers derived from coniferyl alcohol, sinapyl alcohol, their aldehyde analogs, or vanillin. All structures support the recently challenged random chemical coupling hypothesis for lignin polymerization. Importantly, the structures of two oligomers, each containing a g-p-hydroxybenzoylated syringyl unit, strongly suggest that sinapyl p-hydroxybenzoate is an authentic precursor for lignin polymerization in poplar.