Piet Herdewijn

Modifications in lignin and accumulation of phenolic glucosides in poplar xylem upon down-regulation of caffeoyl-coenzyme A O-methyltransferase, an enzyme involved in lignin biosynthesis.

Caffeoyl-coenzyme AO-methyltransferase (CCoAOMT) methylates, in vitro, caffeoyl-CoA and 5-hydroxyferuloyl-CoA, two possible precursors in monolignol biosynthesis in vivo. To clarify the in vivo role of CCoAOMT in lignin biosynthesis, transgenic poplars with 10% residual CCoAOMT protein levels in the stem xylem were generated. Upon analysis of the xylem, the affected transgenic lines had a 12% reduced Klason lignin content, an 11% increased syringyl/guaiacyl ratio in the noncondensed lignin fraction, and an increase in lignin-attached p-hydroxybenzoate but otherwise a lignin composition similar to that of wild type. Stem xylem of the CCoAOMT-down-regulated lines had a pink-red coloration, which coincided with an enhanced fluorescence of mature vessel cell walls. The reduced production of CCoAOMT caused an accumulation ofO 3-β-d-glucopyranosyl-caffeic acid,O 4-β-d-glucopyranosyl-vanillic acid, andO 4-β-d-glucopyranosyl-sinapic acid (GSA), as authenticated by 1H NMR. Feeding experiments showed thatO 3-β-d-glucopyranosyl-caffeic acid and GSA are storage or detoxification products of caffeic and sinapic acid, respectively. The observation that down-regulation of CCoAOMT decreases lignin amount whereas GSA accumulates to 10% of soluble phenolics indicates that endogenously produced sinapic acid is not a major precursor in syringyl lignin biosynthesis. Our in vivo results support the recently obtained in vitroenzymatic data that suggest that the route from caffeic acid to sinapic acid is not used for lignin biosynthesis.

Typing of the EPS coat of Erwinia amylovora strains in relation to their phytopathological properties

The structure and the production of the extracellular polysaccharide (EPS) coat of different E. amylovora isolates were investigated. Mass spectrometry and NMR analysis according to Nimtz et al. (1996) elucidated a different structure in the amylovoran of E. amylovora pathogens on Malaceae and on Rubus host plants. Tests with the E. amylovora pathogens on Malaceae showed a direct correlation between the amount of EPS produced and the aggressiveness of the strains.