Imbalanced Lignin Biosynthesis Promotes the Sexual Reproduction of Homothallic Oomycete Pathogens

Lignin is incorporated into plant cell walls to maintain plant architecture and to ensure long-distance water transport. Lignin composition affects the industrial value of plant material for forage, wood and paper production, and biofuel technologies. Industrial demands have resulted in an increase in the use of genetic engineering to modify lignified plant cell wall composition. However, the interaction of the resulting plants with the environment must be analyzed carefully to ensure that there are no undesirable side effects of lignin modification. We show here that Arabidopsis thaliana mutants with impaired 5-hydroxyguaiacyl O-methyltransferase (known as caffeate O-methyltransferase; COMT) function were more susceptible to various bacterial and fungal pathogens. Unexpectedly, asexual sporulation of the downy mildew pathogen, Hyaloperonospora arabidopsidis, was impaired on these mutants. Enhanced resistance to downy mildew was not correlated with increased plant defense responses in comt1 mutants but coincided with a higher frequency of oomycete sexual reproduction within mutant tissues. Comt1 mutants but not wild-type Arabidopsis accumulated soluble 2-O-5-hydroxyferuloyl-l-malate. The compound weakened mycelium vigor and promoted sexual oomycete reproduction when applied to a homothallic oomycete in vitro. These findings suggested that the accumulation of 2-O-5-hydroxyferuloyl-l-malate accounted for the observed comt1 mutant phenotypes during the interaction with H. arabidopsidis. Taken together, our study shows that an artificial downregulation of COMT can drastically alter the interaction of a plant with the biotic environment

Comparison of macromolecular interactions in the cell walls of hardwood, softwood and maize by fluorescence and FTIR spectroscopy, differential polarization laser scanning microscopy and X-ray diffraction

Interactions between macromolecules in the cell walls of different plant origin were compared, namely spruce wood (Picea omorika (PaniA double dagger) PurkiAe) as an example of softwood, maple wood (Acer platanoides L.) as a hardwood and maize stems (Zea mays L.) as a herbaceous plant from the grass family and widely used agricultural plant. Interactions of macromolecules in isolated cell walls from the three species were compared by using Fourier transform infrared spectroscopy, X-ray diffraction and fluorescence spectroscopy. Linear dichroism of the cell walls was observed by using differential polarization laser scanning microscope (DP-LSM), which provides information of macromolecular order. This method has not previously been used for comparison of the cell walls of various plant origins. It was shown that the maize cell walls have higher amount of hydrogen bonds that lead to more regular packing of cellulose molecules, simpler structure of lignin, and a higher crystallinity of the cell wall in relation to the walls of woody plants. DP-LSM and fluorescence spectroscopy results indicate that maize has simpler and more ordered structure than both woody species. The results of this work provide new data for comparison of the cell wall properties that may be important for selection of appropriate plant for possible applications as a source of biomass. This may be a contribution to the development of efficient deconstruction and separation technologies that enable release of sugar and aromatic compounds from the cell wall macromolecular structure