Genome mapping and gene expression of NDP-sugar pathways in the giant duckweed Spirodela polyrhiza and its relevance for bioenergy

Abstract

Duckweeds are fast-growing aquatic plants suitable for bioenergy due to fermentable-rich biomass with low lignin. The duckweed sub-families Lemnoideae and Wolffioideae are also distinguished by the distribution of two pectin classes (apiogalacturonan and xylogalacturonan), which seem to be related to their growing capacity and the starch content. The plant cell wall is built from pathways of nucleotide sugars syntheses that culminate in cell wall synthesis and deposition. Therefore, understanding these pathways through mapping the genes involved and their expression would be important to develop tools to improve bioenergy production. Here we used the available information of NDP-sugar metabolism to search for orthologous genes involved in the synthesis of cell wall polysaccharides in Spirodela polyrhiza . We detected 190 genes and mapped them onto the plant chromosomes . The genes were roughly arranged in groups according to their category: "Starch and sucrose metabolism," "Pectins," "Hemicelluloses," and "Cellulose." We followed the expression of thirty-eight of the orthologues’ transcripts – the higher expression being starch ( SBE ), pectin ( GAUT1, MUR, USP , and GER ), and mannan ( CSLA ) syntheses - corroborating the chemical composition of S. polyrhiza cell wall . We further investigated the carbohydrate metabolism pathways and discussed the implications of altering the NDP pathways for bioenergy and biorefinery. We conclude that S. polyrhiza displays suitable features for future genetic transformations leading to the adaptation of its cell wall for biofuels. However, such strategies will have to consider the trade-offs between fermentation and ethanol production benefits and the potential adverse effects of genetic transformation on plant growth and development.