title: Engineering secondary cell wall deposition in plants.
abstract: Lignocellulosic biomass was used for thousands of years as animal feed and is now considered a great sugar source for biofuels production. It is composed mostly of secondary cell walls built with polysaccharide polymers that are embedded in lignin to reinforce the cell wall structure and maintain its integrity. Lignin is the primary material responsible for biomass recalcitrance to enzymatic hydrolysis. During plant development, deep reductions of lignin cause growth defects and often correlate with the loss of vessel integrity that adversely affects water and nutrient transport in plants. The work presented here describes a new approach to decrease lignin content while preventing vessel collapse and introduces a new strategy to boost transcription factor expression in native tissues. We used synthetic biology tools in Arabidopsis to rewire the secondary cell network by changing promoter-coding sequence associations. The result was a reduction in lignin and an increase in polysaccharide depositions in fibre cells. The promoter of a key lignin gene, C4H, was replaced by the vessel-specific promoter of transcription factor VND6. This rewired lignin biosynthesis specifically for vessel formation while disconnecting C4H expression from the fibre regulatory network. Secondly, the promoter of the IRX8 gene, secondary cell wall glycosyltransferase, was used to express a new copy of the fibre transcription factor NST1, and as the IRX8 promoter is induced by NST1, this also created an artificial positive feedback loop (APFL). The combination of strategies-lignin rewiring with APFL insertion-enhances polysaccharide deposition in stems without over-lignifying them, resulting in higher sugar yields after enzymatic hydrolysis.
authors.affiliation: Joint BioEnergy Institute, Physical Biosciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Prajakta
authors.initials: P
authors.lastname: Mitra
authors.forename: Ling
authors.initials: L
authors.lastname: Zhang
authors.forename: Lina
authors.initials: L
authors.lastname: Prak
authors.forename: Yves
authors.initials: Y
authors.lastname: Verhertbruggen
authors.forename: Jin-Sun
authors.initials: JS
authors.lastname: Kim
authors.forename: Lan
authors.initials: L
authors.lastname: Sun
authors.forename: Kejian
authors.initials: K
authors.lastname: Zheng
authors.forename: Kexuan
authors.initials: K
authors.lastname: Tang
authors.forename: Manfred
authors.initials: M
authors.lastname: Auer
authors.forename: Henrik V
authors.initials: HV
authors.lastname: Scheller
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D056804:Biofuels; D002473:Cell Wall / Q000378:metabolism*; D025461:Feedback, Physiological; D018506:Gene Expression Regulation, Plant; D005818:Genetic Engineering; D008031:Lignin / Q000096:biosynthesis*; D058526:Plant Vascular Bundle / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D056804:Biofuels; C510498:NST1 protein, Arabidopsis; D014157:Transcription Factors; C585090:VND6 protein, Arabidopsis; D008031:Lignin