Identification of MEDIATOR16 as the <i>Arabidopsis</i> COBRA suppressor MONGOOSE1

Significance The cobra mutants of Arabidopsis , such as cob-6 , have impaired growth associated with a defect in cellulose synthesis. Mutations in MEDIATOR16 ( MED16 ) reduce the number of misregulated genes in cob-6 mutants and suppress the phenotypes. This observation implicates MED16 in transcriptional responses to cell wall defects. Ectopic expression of two pectin methylesterase inhibitors (PMEIs) identified in a suppressor screen partially suppressed the growth defect in the cob-6 mutant. The results confirm that the PMEIs have significant in vivo activity, and provide evidence that pectin esterification can modulate cell wall properties.