Alleles Causing Resistance to Isoxaben and Flupoxam Highlight the Significance of Transmembrane Domains for CESA Protein Function

Abstract

The cellulose synthase (CESA) proteins in Arabidopsis play an essential role in the production of cellulose in the cell walls. Herbicides such as isoxaben and flupoxam specifically target this production process and are prominent cellulose biosynthesis inhibitors (CBIs). Forward genetic screens in Arabidopsis revealed that mutations that can result in varying degrees of resistance to either isoxaben or flupoxam CBI can be attributed to single amino acid substitutions in primary wall CESAs. Missense mutations were almost exclusively present in the predicted transmembrane regions of CESA1, CESA3, and CESA6. Resistance to isoxaben was also conferred by modification to the catalytic residues of CESA3. This resulted in cellulose deficient phenotypes characterized by reduced crystallinity and dwarfism. However, mapping of mutations to the transmembrane regions also lead to growth phenotypes and altered cellulose crystallinity phenotypes. These results provide further genetic evidence supporting the involvement of CESA transmembrane regions in cellulose biosynthesis.

Endosidin20 is a broad-spectrum cellulose synthesis inhibitor with an herbicidal function

“…Three mutations, CESA3 G998D ( ixr1-1 ), CESA3 T942I ( ixr1-2 ) and CESA6 R1064W ( ixr2-1 ) have been found to cause reduced sensitivity to isoxaben (Scheible et al, 2001; Desprez et al, 2002). Isoxaben is thus believed to target CESA directly to inhibit cellulose biosynthesis and has been widely used in cellulose biosynthesis research (Scheible et al, 2001; Desprez et al, 2002; Shim et al, 2018). The originally identified mutations lead to reduced sensitivity to isoxaben are located at the C-terminal region of CESAs while most of the mutations that cause reduced sensitivity to ES20 are located at the central cytoplasmic domain.…”

Interactions between Cellulose and (1,3;1,4)-β-glucans and Arabinoxylans in the Regenerating Wall of Suspension Culture Cells of the Ryegrass Lolium multiflorum

“…This indicates that cellulose deposition is not required for the other NCPs to be deposited or to form their natural, in muro , architecture. While these results do not preclude the presence of amorphous cellulose, isoxaben inhibits cellulose synthases [ 56 , 57 , 66 ], which would suggest that cellulose deposition is largely prevented. The increase in NCPs after this treatment may be a response by this grass species to the reduction in cellulose to increase the wall strength [ 67 ].…”

Updating Insights into the Catalytic Domain Properties of Plant Cellulose synthase (CesA) and Cellulose synthase-like (Csl) Proteins

“…Chemical genetics identified mutants resistant or tolerant against various CBI. Single amino acid substitutions, mostly in the transmembrane regions of CesA , have been reported to confer resistance to CBI, suggesting a critical role of these residues and their proximity to the binding site of the inhibitor [ 91 ]. These CBI-resistant mutant alleles often display reduction in cellulose crystallinity but they do not exhibit any other evident cellulose deficiency [ 61 , 91 ].…”

“…Single amino acid substitutions, mostly in the transmembrane regions of CesA , have been reported to confer resistance to CBI, suggesting a critical role of these residues and their proximity to the binding site of the inhibitor [ 91 ]. These CBI-resistant mutant alleles often display reduction in cellulose crystallinity but they do not exhibit any other evident cellulose deficiency [ 61 , 91 ]. A possible explanation is that the structural changes of CBI binding sites most likely do not disrupt the cellulose synthase catalytic activity.…”

“…A possible explanation is that the structural changes of CBI binding sites most likely do not disrupt the cellulose synthase catalytic activity. There are only a few cases of residue modifications in the catalytic domain of CesA associated with resistance to CBI [ 91 ]. This could be attributed to topological association of these residues with the transmembrane regions, reflecting the complexity of the CesA protein structure and the perplexed mode of CBI binding to specific regions.…”