Expression of fungal acetyl xylan esterase in Arabidopsis thaliana improves saccharification of stem lignocellulose |
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| Authors: | Prashant Mohan‐Anupama Pawar Marta Derba‐Maceluch Sun‐Li Chong Leonardo D Gómez Eva Miedes Alicja Banasiak Christine Ratke Cyril Gaertner Grégory Mouille Simon J McQueen‐Mason Antonio Molina Anita Sellstedt Maija Tenkanen Ewa J Mellerowicz |
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| Affiliation: | 1. Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Ume? Plant Science Centre, Ume?, Sweden;2. Department of Food and Environmental Sciences, University of Helsinki, Helsinki, Finland;3. Center for Novel Agricultural Products Department of Biology, University of York, York, UK;4. Centro de Biotecnología y Genómica de Plantas (UPM‐INIA), Universidad Politécnica de Madrid, Pozuelo de Alarcón, Madrid, Spain;5. Institute of Experimental Biology, University of Wroclaw, Wroclaw, Poland;6. Institut Jean‐Pierre Bourgin UMR 1318 INRA/AgroParisTech, Saclay Plant Sciences, Centre de Versailles‐Grignon, Versailles Cedex, France;7. Department of Plant Physiology, Umea University, Ume? Plant Science Centre, Ume?, Sweden |
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| Abstract: | Cell wall hemicelluloses and pectins are O‐acetylated at specific positions, but the significance of these substitutions is poorly understood. Using a transgenic approach, we investigated how reducing the extent of O‐acetylation in xylan affects cell wall chemistry, plant performance and the recalcitrance of lignocellulose to saccharification. The Aspergillus niger acetyl xylan esterase AnAXE1 was expressed in Arabidopsis under the control of either the constitutively expressed 35S CAMV promoter or a woody‐tissue‐specific GT43B aspen promoter, and the protein was targeted to the apoplast by its native signal peptide, resulting in elevated acetyl esterase activity in soluble and wall‐bound protein extracts and reduced xylan acetylation. No significant alterations in cell wall composition were observed in the transgenic lines, but their xylans were more easily digested by a β‐1,4‐endoxylanase, and more readily extracted by hot water, acids or alkali. Enzymatic saccharification of lignocellulose after hot water and alkali pretreatments produced up to 20% more reducing sugars in several lines. Fermentation by Trametes versicolor of tissue hydrolysates from the line with a 30% reduction in acetyl content yielded ~70% more ethanol compared with wild type. Plants expressing 35S:AnAXE1 and pGT43B:AnAXE1 developed normally and showed increased resistance to the biotrophic pathogen Hyaloperonospora arabidopsidis, probably due to constitutive activation of defence pathways. However, unintended changes in xyloglucan and pectin acetylation were only observed in 35S:AnAXE1‐expressing plants. This study demonstrates that postsynthetic xylan deacetylation in woody tissues is a promising strategy for optimizing lignocellulosic biomass for biofuel production. |
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| Keywords: | acetyl xylan esterase biofuels saccharification O‐acetylation glucuronoxylan secondary cell wall |
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