Date Published: December 23, 2014
Publisher: Public Library of Science
Author(s): Li Tan, Yunqiao Pu, Sivakumar Pattathil, Utku Avci, Jin Qian, Allison Arter, Liwei Chen, Michael G. Hahn, Arthur J. Ragauskas, Marcia J. Kieliszewski, Joshua L. Heazlewood.
Extensins are one subfamily of the cell wall hydroxyproline-rich glycoproteins, containing characteristic SerHyp4 glycosylation motifs and intermolecular cross-linking motifs such as the TyrXaaTyr sequence. Extensins are believed to form a cross-linked network in the plant cell wall through the tyrosine-derivatives isodityrosine, pulcherosine, and di-isodityrosine. Overexpression of three synthetic genes encoding different elastin-arabinogalactan protein-extensin hybrids in tobacco suspension cultured cells yielded novel cross-linking glycoproteins that shared features of the extensins, arabinogalactan proteins and elastin. The cell wall properties of the three transgenic cell lines were all changed, but in different ways. One transgenic cell line showed decreased cellulose crystallinity and increased wall xyloglucan content; the second transgenic cell line contained dramatically increased hydration capacity and notably increased cell wall biomass, increased di-isodityrosine, and increased protein content; the third transgenic cell line displayed wall phenotypes similar to wild type cells, except changed xyloglucan epitope extractability. These data indicate that overexpression of modified extensins may be a route to engineer plants for bioenergy and biomaterial production.
Plants are the major source of food and chemicals on earth. With our intensifying desire for sustainable energy, the engineering of plants, in particular their cell walls, to achieve greater biofuel production is a major focus of current cell wall research. Genetic manipulation of plants using gene transformation or selective breeding allows the production plants possessing higher biomass and digestibility –.
Overexpression of extensin analogs in tobacco primary cell walls resulted in changes of wall properties that were distinct for each transgenic cell line. The arrangement and sizes of the extensin motifs, AGP motifs, and elastin motifs on the polypeptide affected the effects on overall wall structure for each line. The 442-EGFP walls showed no change in wall cellulose crystallinity; however, wall saturated with 442-EGFP may have prevented the formation of endogenous extensin network, which significantly changed wall physical and chemical properties. In contrast, the 224-EGFP walls exhibited a higher ratio of xyloglucans to celluloses and lower cellulose crystallinity, most likely due to the spatial alterations caused by deposition of the more extended 224-EGFP fusion glycoproteins. However, the 242-EGFP walls only displayed changes in xyloglucan extractability. These results indicate that regulated expression of modified extensins in planta may be a way to manipulate wall architecture to achieve higher biomass and higher biofuel production.