title: Disruption of Mediator rescues the stunted growth of a lignin-deficient Arabidopsis mutant.
abstract: Lignin is a phenylpropanoid-derived heteropolymer important for the strength and rigidity of the plant secondary cell wall. Genetic disruption of lignin biosynthesis has been proposed as a means to improve forage and bioenergy crops, but frequently results in stunted growth and developmental abnormalities, the mechanisms of which are poorly understood. Here we show that the phenotype of a lignin-deficient Arabidopsis mutant is dependent on the transcriptional co-regulatory complex, Mediator. Disruption of the Mediator complex subunits MED5a (also known as REF4) and MED5b (also known as RFR1) rescues the stunted growth, lignin deficiency and widespread changes in gene expression seen in the phenylpropanoid pathway mutant ref8, without restoring the synthesis of guaiacyl and syringyl lignin subunits. Cell walls of rescued med5a/5b ref8 plants instead contain a novel lignin consisting almost exclusively of p-hydroxyphenyl lignin subunits, and moreover exhibit substantially facilitated polysaccharide saccharification. These results demonstrate that guaiacyl and syringyl lignin subunits are largely dispensable for normal growth and development, implicate Mediator in an active transcriptional process responsible for dwarfing and inhibition of lignin biosynthesis, and suggest that the transcription machinery and signalling pathways responding to cell wall defects may be important targets to include in efforts to reduce biomass recalcitrance.
authors.affiliation: 1] Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA [2] Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis, Indiana 46268, USA (N.D.B.); Department of Agronomy, University of Wisconsin-Madison, 1575 Linden Drive, Madison, Wisconsin 53706, USA (J.M.).
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Bonawitz
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Jeong Im
authors.initials: JI
authors.lastname: Kim
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tobimatsu
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Peter N
authors.initials: PN
authors.lastname: Ciesielski
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Nickolas A
authors.initials: NA
authors.lastname: Anderson
authors.affiliation: Department of Agricultural and Biological Engineering and the Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Ximenes
authors.affiliation: 1] Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA [2] Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis, Indiana 46268, USA (N.D.B.); Department of Agronomy, University of Wisconsin-Madison, 1575 Linden Drive, Madison, Wisconsin 53706, USA (J.M.).
authors.forename: Junko
authors.initials: J
authors.lastname: Maeda
authors.affiliation: 1] Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA [2] Department of Biological Systems Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA [3] DOE Great Lakes Bioenergy Research Center, and Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin 53726, USA.
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Bryon S
authors.initials: BS
authors.lastname: Donohoe
authors.affiliation: 1] Department of Agricultural and Biological Engineering and the Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, Indiana 47907, USA [2] Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Ladisch
authors.affiliation: Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Clint
authors.initials: C
authors.lastname: Chapple
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D056804:Biofuels; D018533:Biomass; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D008031:Lignin / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D056892:Mediator Complex / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D030821:Plants, Genetically Modified; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D056804:Biofuels; D056892:Mediator Complex; D021122:Protein Subunits; D002482:Cellulose; D008031:Lignin