Arabidopsis GELP7 is plasma membrane-localized acetyl xylan esterase, and its overexpression improves saccharification efficiency.

Abstract

Acetyl substitution on the xylan chain is critical for stable interaction with cellulose and other cell wall polymers in the secondary cell wall. Xylan acetylation pattern is governed by Golgi and extracellular localized acetyl xylan esterase (AXE). We investigated the role of Arabidopsis clade Id from the GDSL esterase/lipase or GELP family in polysaccharide deacetylation. The investigation of the AtGELP7 T-DNA mutant line showed a decrease in stem esterase activity and an increase in stem acetyl content. We further generated overexpressor AtGELP7 transgenic lines, and these lines showed a decrease in xylan acetylation in comparison with wild type plants. Therefore, we have named this enzyme as AtAXE1. The subcellular localization studies showed that the AtAXE1 enzyme is secreted out, associated with the plasma membrane and involved in xylan de-esterification post-synthesis. The cellulose digestibility was improved in AtAXE1 overexpressor lines without pre-treatment, after alkali and xylanases pre-treatment. Furthermore, we have also established that the AtGELP7 gene is upregulated in the overexpressor line of AtMYB46, which is a secondary cell wall specific transcription factor. This transcriptional regulation can drive AtGELP7 or AtAXE1 to perform de-esterification of xylan in a tissue-specific manner.