CRISPR‐Cas9 editing of CAFFEOYL SHIKIMATE ESTERASE 1 and 2 shows their importance and partial redundancy in lignification in Populus tremula × P. alba. Issue 11 (6th August 2021)

• Record Type: Journal Article
• Authors: de Vries, Lisanne; Brouckaert, Marlies; Chanoca, Alexandra; Kim, Hoon; Regner, Matthew R.; Timokhin, Vitaliy I.; Sun, Yi; De Meester, Barbara; Van Doorsselaere, Jan; Goeminne, Geert; Chiang, Vincent L.; Wang, Jack P.; Ralph, John; Morreel, Kris; Vanholme, Ruben; Boerjan, Wout
• Is Part Of: Plant biotechnology journal. Volume 19:Issue 11(2021)
• Page Start: 2221
• Page End: 2234
• Publication Date: 2021-08-06
• Subjects: poplar -- CRISPR‐Cas9 -- CSE -- lignin -- phenylpropanoids -- metabolic engineering; Plant biotechnology -- Periodicals; Plant genetic engineering -- Periodicals; 630.272
• DOI: 10.1111/pbi.13651
• Languages: English
• ISSNs: 1467-7644

Abstract

Summary: Lignins are cell wall‐located aromatic polymers that provide strength and hydrophobicity to woody tissues. Lignin monomers are synthesized via the phenylpropanoid pathway, wherein CAFFEOYL SHIKIMATE ESTERASE (CSE) converts caffeoyl shikimate into caffeic acid. Here, we explored the role of the two CSE homologs in poplar ( Populus tremula × P. alba ). Reporter lines showed that the expression conferred by both CSE1 and CSE2 promoters is similar. CRISPR‐Cas9‐generated cse1 and cse2 single mutants had a wild‐type lignin level. Nevertheless, CSE1 and CSE2 are not completely redundant, as both single mutants accumulated caffeoyl shikimate. In contrast, the cse1 cse2 double mutants had a 35% reduction in lignin and associated growth penalty. The reduced‐lignin content translated into a fourfold increase in cellulose‐to‐glucose conversion upon limited saccharification. Phenolic profiling of the double mutants revealed large metabolic shifts, including an accumulation of p ‐coumaroyl, 5‐hydroxyferuloyl, feruloyl and sinapoyl shikimate, in addition to caffeoyl shikimate. This indicates that the CSEs have a broad substrate specificity, which was confirmed by in vitro enzyme kinetics. Taken together, our results suggest an alternative path within the phenylpropanoid pathway at the level of the hydroxycinnamoyl‐shikimates, and show that CSE is a promising target to improve plants for the biorefinery.