Even though improved saccharification of transgenic trees has been obtained without growth penalties, most often increased saccharification is associated with impaired growth. A critical aspect of improving saccharification of Populus trees has been the risk for growth penalties when modifying wood properties for reduced recalcitrance. Advantages of Populus trees include their high biomass production rate (25 Mg ha −1 year −1), genetic diversity, market opportunities, and advanced genomic tools. The most commonly studied species belong to the Populus family, including poplar and aspen trees. Numerous initiatives have been taken to improve saccharification in forest feedstocks by transgenic means.
Identification of novel genes and/or pathways that control wood properties and growth of trees, therefore, provides a foundation not only for genetic improvement of the quality and quantity of wood, but also for improved saccharification efficiency and convertibility of woody biomass. Although wood is rather well characterized chemically and anatomically, the knowledge on genetic pathways that could be manipulated to reduce feedstock recalcitrance without compromising the properties and formation of wood is still scarce. In this process, the major challenge is the recalcitrance of the biomass mainly due to prevention of access of enzymes to cellulose by hemicelluloses and lignin, high degree of cellulose polymerization, covalent cross-linkages between lignin and hemicelluloses, and other factors that remain to be determined. One way to deconstruct the biomass is through pretreatment and enzymatic saccharification, which results in the release of sugars from cellulose and hemicelluloses. Wood and other lignocellulosic feedstocks can serve as an abundant renewable source of sugars and other platform molecules for the production of advanced biofuels, green chemicals, and bio-based materials. Furthermore, multi-omic analyses, including transcriptomic, proteomic and metabolomic analyses, performed here provide a toolbox for future studies on the function of VAP27 proteins in plants. The results demonstrate the usefulness of gene-mining programs to identify novel genes with the potential to improve biofuel production in tree biotechnology programs. Tendencies to increased glucose yields by up to 24% were present on a whole tree biomass basis after acidic pretreatment and enzymatic saccharification also in the transgenic trees grown for 5 years on the field when compared to the wild-type control. The glucose yield after enzymatic saccharification with a prior hydrothermal pretreatment step with sulfuric acid was not increased in the greenhouse-grown transgenic trees on a dry-weight basis, but increased by 26–50% when calculated on a whole biomass basis in comparison to the wild-type control.
Analytical-scale enzymatic saccharification without any pretreatment revealed for all greenhouse-grown transgenic lines, compared to the wild type, a 20–44% increase in the glucose yield per dry weight after enzymatic saccharification, even though it was statistically significant only for one line. The transgenic lines carried an overexpression construct for Populus tremula × tremuloides vesicle-associated membrane protein (VAMP)-associated protein PttVAP27-17 that was selected from a gene-mining program for novel regulators of wood formation. In this study, we report on transgenic hybrid aspen ( Populus tremula × tremuloides) lines that showed potential to increase biomass production both in the greenhouse and after 5 years of growth in the field.
Targeted modification of the chemical composition of the feedstock can improve saccharification but this gain is often abrogated by concomitant reduction in tree growth. Bioconversion of wood into bioproducts and biofuels is hindered by the recalcitrance of woody raw material to bioprocesses such as enzymatic saccharification.
0 kommentar(er)
