Structural Characterization of Modified Lignin in Transgenic Tobacco Plants in Which the Activity of 4-Coumarate:Coenzyme A Ligase Is Depressed

Abstract

Transgenic tobacco (Nicotiana tabacum 1.) plants in which the activity of 4-coumarate:coenzyme A ligase is very low contain a novel lignin in their xylem. Details of changes in hydroxycinnamic acids bound to cell walls and in the structure of the novel lignin were identified by base hydrolysis, alkaline nitrobenzene oxidation, pyrolysis-gas chromatography, and '3C-nuclear magnetic resonance analysis. In the brownish tissue of the transgenic plants, the levels of three hydroxycinnamic acids, p-coumaric, ferulic, and sinapic, which were bound to cell walls, were apparently increased as a result of down-regulation of the expression of the gene for 4-coumarate:coenzyme A ligase. Some of these hydroxycinnamic acids were linked to cell walls via ester and ether linkages. The accumulation of hydroxycinnamic acids also induced an increase in the leve1 of condensed units in the novel lignin of the brownish tissue. Our data indicate that the behavior of some of the incorporated hydroxycinnamic acids resembles lignin monomers in the brownish tissue, and their accumulation results in dramatic changes in the biosynthesis of lignin in transgenic plants.The deposition of lignin in vascular cell walls is a key step in the differentiation of these cells into the functional elements that participate in the transport of water and in the structural support of plants. The biosynthesis of lignin has been studied extensively and the major enzymes involved in the synthesis of precursors to lignin have been identified (Higuchi, 1985; Lewis and Yamamoto, 1990). In the past decade many genes for enzymes related to the biosynthesis of lignin have been cloned from a variety of plant species, and the expression of these genes at various stages of lignification has been characterized (Sederoff et al., 1994; Whetten and Sederoff, 1995). In several recent studies transgenic plants carrying chimeric genes for the enzymes involved in lignin biosynthesis were generated and the altered lignins in these transformants were analyzed (Elkind et al

Essential Role of Caffeoyl Coenzyme A O-Methyltransferase in Lignin Biosynthesis in Woody Poplar Plants

“…Coloration of xylem or wood has been reported in transgenic plants or mutants with repression of other lignin pathway genes such as COMT, 4-coumarate: coenzyme A ligase, and cinnamyl alcohol dehydrogenase (Halpin et al, 1994;Atanassova et al, 1995;Doorsselaere et al, 1995;Campbell and Sederoff, 1996;Kajita et al, 1997;Ralph et al, 1997;Tsai et al, 1998). Xylem or wood in plants with repression of COMT or cinnamyl alcohol dehydrogenase often shows strong red coloration, which has been attributed to the accumulation of hydroxycinnamyl aldehydes (Halpin et al, 1994;Higuchi et al, 1994;Ralph et al, 1997;Stewart et al, 1997;Tsai et al, 1998).…”

“…Xylem or wood in plants with repression of COMT or cinnamyl alcohol dehydrogenase often shows strong red coloration, which has been attributed to the accumulation of hydroxycinnamyl aldehydes (Halpin et al, 1994;Higuchi et al, 1994;Ralph et al, 1997;Stewart et al, 1997;Tsai et al, 1998). In plants with repression of 4-coumarate-coenzyme A ligase, xylem displayed a brownish color, probably due to accumulation of hydroxycinnamic acids (Kajita et al, 1997). It is obvious that the coloration of wood with repression of CCoAOMT could not be caused by hydroxycinnamyl aldehydes because the CCoAOMT-mediated reaction is at the early step of the phenylpropanoid pathway.…”

Differential Substrate Inhibition Couples Kinetically Distinct 4-Coumarate:Coenzyme A Ligases with Spatially Distinct Metabolic Roles in Quaking Aspen

“…Questions remain as to why certain species appear to possess multiple, apparently similar, 4CL isoforms, whereas others such as potato (Solanum tuberosum) and pine (Pinus taeda) do not (BeckerAndré et al, 1991;Voo et al, 1995;Zhang and Chiang, 1997). If the possibility is accepted that isoforms expressed in specialized tissues of certain species have specific and distinct roles, then it is also possible that those isoforms are more specialized and differ more strikingly and with greater consequences in vivo than would be concluded from the in vitro studies to date.Analysis of transgenic tobacco (Nicotiana tabacum) and aspen plants revealed strikingly unequal effects of 4CL down-regulation on in vivo utilization of its three most preferred substrates, PA, CA, and FA (Kajita et al, 1997;Hu et al, 1999 Article, publication date, and citation information can be found at www.plantphysiol.org/cgi …”

“…Analysis of transgenic tobacco (Nicotiana tabacum) and aspen plants revealed strikingly unequal effects of 4CL down-regulation on in vivo utilization of its three most preferred substrates, PA, CA, and FA (Kajita et al, 1997;Hu et al, 1999 Article, publication date, and citation information can be found at www.plantphysiol.org/cgi…”

Genetic Transformation in Conifers

“…Prese~~tly, it is difficult to anticipate the consequences of genetic manipulation of the biosynthetic pathways of lignin on growth, develop~ner~tal and morphogenetic behavior of pli~nts. Several attempts have bee11 made to genetically ma~lipulate lignin biosynthesis via the transge~~ic approi~cli (Sederoff et (I/., 1994;Atanasova et al, 1995;Doorsselaere et al, 1995;Kajita et al, 1997). In addition to co~~tributing to the strength of wood, lignin also plays a crucial role in the ability of wood to resist pathogen infection and rotting.…”