Identification of MEDIATOR16 as the Arabidopsis COBRA suppressor MONGOOSE1

Abstract

We performed a screen for genetic suppressors of cobra, an Arabidopsis mutant with defects in cellulose formation and an increased ratio of unesterified/esterified pectin. We identified a suppressor named mongoose1 (mon1) that suppressed the growth defects of cobra, partially restored cellulose levels, and restored the esterification ratio of pectin to wild-type levels. mon1 was mapped to the MEDIATOR16 (MED16) locus, a tail mediator subunit, also known as SENSITIVE TO FREEZING6 (SFR6). When separated from the cobra mutation, mutations in MED16 caused resistance to cellulose biosynthesis inhibitors, consistent with their ability to suppress the cobra cellulose deficiency. Transcriptome analysis revealed that a number of cell wall genes are misregulated in med16 mutants. Two of these genes encode pectin methylesterase inhibitors, which, when ectopically expressed, partially suppressed the cobra phenotype. This suggests that cellulose biosynthesis can be affected by the esterification levels of pectin, possibly through modifying cell wall integrity or the interaction of pectin and cellulose.cell wall | cellulose | freezing tolerance | pectin | transcription

Cellulose Deficiency Is Enhanced on Hyper Accumulation of Sucrose by a H+-Coupled Sucrose Symporter

“…4B). The iC4-sC4 ratio is analogous to crystallinity and has been reported to be altered in several cellulose-deficient mutants (Harris et al, 2012;Sorek et al, 2015). In our experiment, the wild type was found to have an iC4:sC4 ratio of 0.65 and shv3svl1 was found to have an iC4:sC4 ratio of 0.68, indicating that microfibril structure, in terms of this metric, is essentially unaltered in the shv3svl1 mutant (Fig.…”

“…Quantitative 13 C direct polarization magic-angle-spinning solid-state NMR spectroscopy was performed as described by Sorek et al (2015). Because of the technical limitation imposed by the necessity of uniform 13 C labeling, we could not compare the structure of cellulose from seedlings grown in the absence of exogenous sugars by this method.…”

Apple fruit superficial scald resistance mediated by ethylene inhibition is associated with diverse metabolic processes

“…COBRA is a glycosylphosphatidylinositol‐anchored protein involved in the biosynthesis of cellulose, a major polysaccharide in both primary and secondary cell walls (Li et al ., ; Cao et al ., ). Transgenic A. thaliana lines overexpressing the COBRA‐encoding cob‐6 gene showed an improved tolerance to cold stress (Sorek et al ., ). These lines also showed a reduced level of pectin esterification, which might contribute to the induction of cold stress resistance.…”

The Plastid Lipocalin LCNP Is Required for Sustained Photoprotective Energy Dissipation in Arabidopsis

“…Mapping by sequencing in Arabidopsis has recently been proven successful in several studies to determine the causative mutation of a specific phenotype (Schneeberger et al, 2009;Sorek et al, 2015). To this aim, we backcrossed the mutant #205 to the parental strain soq1 npq4 used for the EMS mutagenesis and selected individuals that lacked qH from the F2 progeny (which represent onequarter of the individuals with genotype soq1 npq4 and homozygous for the new mutation).…”