Vessel- and ray-specific monolignol biosynthesis as an approach to engineer fiber-hypolignification and enhanced saccharification in poplar |
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Authors: | Barbara De Meester Ruben Vanholme Lisanne de Vries Marlies Wouters Jan Van Doorsselaere Wout Boerjan |
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Affiliation: | 1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, Ghent, 9052 Belgium;2. Higher Institute for Nursing and Biotechnology, VIVES University College, Wilgenstraat 32, Roeselare, 8800 Belgium |
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Abstract: | Lignin is one of the main factors determining recalcitrance to processing of lignocellulosic biomass towards bio-based materials and fuels. Consequently, wood of plants engineered for low lignin content is typically more amenable to processing. However, lignin-modified plants often exhibit collapsed vessels and associated growth defects. Vessel-specific reintroduction of lignin biosynthesis in dwarfed low-lignin cinnamoyl-CoA reductase1 (ccr1) Arabidopsis mutants using the ProSNBE:AtCCR1 construct overcame the yield penalty while maintaining high saccharification yields, and showed that monolignols can be transported between the different xylem cells acting as ‘good neighbors’ in Arabidopsis. Here, we translated this research into the bio-energy crop poplar. By expressing ProSNBE:AtCCR1 into CRISPR/Cas9-generated ccr2 poplars, we aimed for vessel-specific lignin biosynthesis to: (i) achieve growth restoration while maintaining high saccharification yields; and (ii) study the existence of ‘good neighbors’ in poplar wood. Analyzing the resulting ccr2 ProSNBE:AtCCR1 poplars showed that vessels and rays act as good neighbors for lignification in poplar. If sufficient monolignols are produced by these cells, monolignols migrate over multiple cell layers, resulting in a restoration of the lignin amount to wild-type levels. If the supply of monolignols is limited, the monolignols are incorporated into the cell walls of the vessels and rays producing them and their adjoining cells resulting in fiber hypolignification. One such fiber-hypolignified line had 18% less lignin and, despite its small yield penalty, had an increase of up to 71% in sugar release on a plant base upon saccharification. |
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Keywords: | lignin lignin engineering lignin modification-induced dwarfism good neighbors for lignification Populus tremula × P. alba fiber hypolignification saccharification ProSNBE CRISPR/Cas9 CCR |
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