The Mediator complex subunits MED25/PFT1 and MED8 are required for transcriptional responses to changes in cell wall arabinose composition and glucose treatment in Arabidopsis thaliana.
BACKGROUND
Plant cell walls are dynamic structures involved in all aspects of plant growth, environmental interactions and defense responses, and are the most abundant renewable source of carbon-containing polymers on the planet. To balance rigidity and extensibility, the composition and integrity of cell wall components need to be tightly regulated, for example during cell elongation.


RESULTS
We show that mutations in the MED25/PFT1 and MED8 subunits of the Mediator transcription complex suppressed the sugar-hypersensitive hypocotyl elongation phenotype of the hsr8-1 mutant, which has cell wall defects due to arabinose deficiency that do not permit normal cell elongation. This suppression occurred independently of light and jasmonic acid (JA) signaling. Gene expression analyses revealed that the expression of genes induced in hsr8-1 that encode enzymes and proteins that are involved in cell expansion and cell wall strengthening is reduced in the pft1-2 mutant line, and the expression of genes encoding transcription factors involved in reducing hypocotyl cell elongation, genes encoding cell wall associated enzymes and proteins is up-regulated in pft1-2. PFT1 was also required for the expression of several glucose-induced genes, including those encoding cell wall components and enzymes, regulatory and enzymatic components of anthocyanin biosynthesis, and flavonoid and glucosinolate biosynthetic pathways.


CONCLUSIONS
These results establish that MED25 and MED8 subunits of the Mediator transcriptional complex are required for the transcriptional regulation of genes involved in cell elongation and cell wall composition in response to defective cell walls and in sugar- responsive gene expression.
Cell and Developmental Biology Department, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. mathilde.seguela@versailles.inra.fr.|INRA, Institut Jean-Pierre Bourgin, UMR1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, 78000, Versailles, France. mathilde.seguela@versailles.inra.fr.
Mathilde
M
Seguela-Arnaud
Cell and Developmental Biology Department, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. caroline.smith@jic.ac.uk.
Caroline
C
Smith
Nottingham Arabidopsis Stock Centre, University of Nottingham, School of Biosciences, Loughborough, LE12 5RD, UK. marcos@arabidopsis.org.uk.
Marcos Castellanos
MC
Uribe
Nottingham Arabidopsis Stock Centre, University of Nottingham, School of Biosciences, Loughborough, LE12 5RD, UK. sean@arabidopsis.org.uk.
Sean
S
May
Cell and Developmental Biology Department, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. harry.fischl@lincoln.ox.ac.uk.|Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK. harry.fischl@lincoln.ox.ac.uk.
Harry
H
Fischl
Cell and Developmental Biology Department, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. neil.mckenzie@jic.ac.uk.
Neil
N
McKenzie
Cell and Developmental Biology Department, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. michael.bevan@jic.ac.uk.
Michael W
MW
Bevan
D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001089:Arabinose / Q000378:metabolism*; D002473:Cell Wall / Q000201:enzymology / Q000378:metabolism; D004268:DNA-Binding Proteins; D018506:Gene Expression Regulation, Plant; D005947:Glucose / Q000378:metabolism*; D018546:Hypocotyl / Q000235:genetics; D056892:Mediator Complex / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism
D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C000607370:MED8 protein, Arabidopsis; D056892:Mediator Complex; D009687:Nuclear Proteins; C475686:PFT1 protein, Arabidopsis; D001089:Arabinose; D005947:Glucose