Phenotyping transgenic poplar downregulating PtaUGT72E1 to assess the role of this gene in lignin accumulation

In plants, UDP - glycosyltransferases (UGT) are a superfamily of enzymes catalysing the transfer of glycosyl groups to a wide range of molecules like hormones, xenobiotics and secondary metabolites, ... These enzymes are crucial in many environmental adaptation mechanisms. In Arabidopsis thaliana, the UGT72E family was shown to function with monolignols, deriving from the phenylpropanoid pathway. Monolignols are the precursors of many essential compounds for plant growth and development, like intracellular di-, tri- or oligolignols which are considered to have plant defense properties. In the cell wall, they can polymerised to form lignin. It is a complex polymer, which has a role in plant support and allows, thanks to its hydrophobic character, the conduction of water and solutes in the xylem. Currently, our knowledge on the regulation mechanisms of monolignol polymerization into lignin and lignans remains limited. The glycosylation of monolignols and their storage in the vacuole are considered as central mechanisms for monolignol homeostasis. The purpose of this work is to gain a better knowledge on the role of UGT72E in woody plants, producing a large amount of lignin, by characterizing PtaUGT72E1 in Populus tremula x P. alba (clone INRA 717-1B4). One of the strategies chosen is the phenotyping of transgenic poplar over-expressing and down-regulating PtaUGT72E1. A particular focus was made on stem lignification. Two methods were chosen to analyse this aspect: fluorescent analysis of safrani ne staining and Raman spectroscopy. Both methods confirm the alteration of lignin deposition in the xylem cellular wall in transgenic lines: a decrease of lignification was recorded in the over-expressing lines and an increase of lignification in the down-regulating lines. These results highlight a possible role for PtaUGT72E1 in the regulation of the lignification of vascular tissues in poplar.