Untersuchungen zu Monolignolbiosynthese-Mutanten und den CCR Genen in Arabidopsis thaliana

  • Examinations of monolignolbiosynthesis mutants and CCR genes in Arabidopsis thaliana

Masur, Clarissa; Schlaich, Nikolaus Ludwig (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2010)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2010

Abstract

Producing plants with reduced or suitably altered lignin are desirable industrial goals allow reduced energy input in paper mills and to obtain biomass that can be more efficiently fermented. Lignin is a water-insoluble complex phenolic polymer made up of condensed phenylpropanoid subunits. The enzyme Cinnamyl CoA reductase (CCR) catalyses the synthesis of cinnamaldehydes from the corresponding CoA esters of the cinnamic acids prior to their further reduction by cinnamylalcohol dehydrogenases to monolignols.The monolignol subunits undergo stereoselective oxidative coupling under the control of peroxidases and an auxillary (dirigent) protein to produce a random polymer. Lignin is present in secondary plant cell walls and is an essential component of conducting and supportive structural tissue (e.g. wood) in the plant body. Lignin is very resistant to enzymatic attack and due to its impervious nature, lignin deposition in primary cell walls is a component of plant defence against infection. The purpose of this work, which was part of a collaborative project between several groups, was to address different aspects of the role of lignin in defence in the model plant A. thaliana. Ten Arabidopsis thaliana lignin biosynthesis mutants which had altered lignin amount and composition were provided by the other partners for testing. The interaction phenotype of Pseudomonas syringae pv. tomato DC3000 (virulent and avirulent strains), the necrotrophic fungus Alternaria brassicicola and the non-host obligate biotroph Blumeria graminis f. sp. hordei with mutant plants was investigated microscopically and compared to wild type plants. The control and localization of the expression of the CCR1 and CCR2 genes coding for two CCR isozymes was investigated using reporter construct lines provided by the other partners. One can say that, in general, increased pathogen growth was correlated with altered and reduced lignin content. Increased CCR1 and CCR2 expression in leaves was shown after infection in uidA reporter gene lines and confirmed by semi-quantitative PCR and Northern blot analysis. In addition the tissue and developmental specific expression of CCR1 and CCR2 in flowers was shown. The results presented here and the overall results of the collaborative project clearly show, that deleting monolignol biosynthetic genes can in fact reduce lignin content and/or composition. However, this comes with the risk of increased susceptibility to various pathogens.

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