Characterization of two Physcomitrella patens Caffeoyl coenzyme A O-methyltransferase-like proteins

Lignin is one of the most abundant biopolymers. It accounts for up to 25% of plant biomass in the biosphere. Lignified cell walls represent an important evolutionary step in plant adaptation to land life. This adaptation provided structural support, nutrient transport, protection from UV radiation, desiccation stress and protection from herbivores and pathogens. Due to lignin’s long half-life, it has become a major carbon sink, causing depletion of the CO2 levels and an increase in O2 levels. Currently lignin research is important for the forage and biofuel industries. It has been seen that a reduction in lignin content leads to higher digestibility and higher release of cellulose from plants. Caffeoyl coenzyme A O-methyltransferases (CCoAOMTS) are a class of enzymes that transfer a methyl group from S-adenosylmethionine to an alcohol group. These enzymes are necessary for lignin production in plants. Previous work has shown that knocking down the function of this enzyme in higher plants caused a decrease in lignin content. Physcomitrella patens is a moss, which is considered not to synthesize lignin but it contains genes for the full lignin biosynthesis pathway. Currently there is some evidence of lignin-like compounds occurring in moss, but evidence of a truly lignified cell wall does not exist. This study looks at two specific enzymes from Physcomitrella patens, Pp-OMT1 and Pp-OMT2. These enzymes resemble CCoAOMTs. Both enzymes were tested for substrate specificity and compared to a true caffeoyl coenzyme A O-methyltransferase from Arabidopsis thalina, AtCCoAOMT1. Furthermore kinetics of Pp-OMT2 and AtCCoAOMT1 were compared. Our results showed that Pp-OMT2 is likely to be a true CCoAOMT while Pp-OMT1 is not. M.S.Includes bibliographical referencesby Sergei Pilipetski