Expression of fungal acetyl xylan esterase in Arabidopsis thaliana improves saccharification of stem lignocellulose

Abstract

SummaryCell 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 b-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.

Defense Responses in Aspen with Altered Pectin Methylesterase Activity Reveal the Hormonal Inducers of Tyloses

“…Deregulation of many different cell wall biosynthetic processes has been shown to constitutively activate JAand ET-dependent and -independent stress signaling pathways (Ellis et al, 2002;Hernández-Blanco et al, 2007) and to increase resistance to abiotic stresses (Keppler and Showalter, 2010) or pathogens (Vogel et al, 2002(Vogel et al, , 2004Hernández-Blanco et al, 2007;Manabe et al, 2011;Pogorelko et al, 2013;Pawar et al, 2016). The induction of tyloses as a result of cell wall defects has been studied only in transgenic poplars with reduced lignin biosynthesis (Kitin et al, 2010), but the current study on PME deregulated plants suggest that increased susceptibility to tyloses formation is likely to be a concern in other cell wall-related mutants and transgenic plants.…”

Genome Analysis of a Zygomycete Fungus Choanephora cucurbitarum Elucidates Necrotrophic Features Including Bacterial Genes Related to Plant Colonization

“…This family is only conserved in zygomycetes among all fungal clades29, but it is also found in bacterial and plant genomes (http://www.cazy.org/CE6.html). The CE6 family is annotated with “acetyl xylan esterase” and it improves the saccharification of stem lignocellulose by deacetylating xylan41. The gene tree of CE6 family indicated that the fungal CE6 genes were more diverged from the common ancestor of plants and the bacterial CE6 family (Supplementary Figure S10).…”

Advances in Genetic Manipulation of Lignocellulose to Reduce Biomass Recalcitrance and Enhance Biofuel Production in Bioenergy Crops

“…Size reduction not only increases the specific surface area of biomass but also reduces cellulose DP and Crl, but it depends on biomass compositions [140][141][142][143][144][145][146][147][148][149][150][151][152]. Liu et al [132] investigated the effect of steam explosion pretreatment on corn stalk particle size for enhancing enzyme digestibility and the result shown that the amount of secondary product was higher and sugar recovery was lower for larger biomass particle size; although, during enzymatic hydrolysis sugar conversion and yield were higher.…”