CELLULOSE BIOSYNTHESIS INHIBITORS: THEIR USES AS POTENTIAL HERBICIDES AND AS TOOLS IN CELLULOSE AND CELL WALL STRUCTURAL PLASTICITY RESEARCH
Authors: Acebes, Antonio Encina, Penélope García-Angulo et al.
Abstract: Cellulose biosynthesis inhibitors (CBIs) form a heterogeneous group of structurally unrelated compounds that specifically affect the assembly or the deposition of cellulose. With the exception of thaxtomin A, the only naturally occurring CBI, all other CBIs are synthetic compounds. A number of them (dichlobenil, isoxaben and flupoxam) are used as herbicides and, as such, are listed as group L in the Herbicide Resistance Action Committee classification of herbicides. Recently, targets for isoxaben and dichlobenil have been provided. Other compounds, such as triazofenamide, CGA 325'615, the aminotriazine AE F150944 or the thiazolidinone named compound 1 have proven to be CBIs, but they have not yet been commercialized. Finally, some drugs seems to display a dual effect, acting as CBIs in some cases (i.e., depending on the species or their concentration), or as auxin herbicide (quinclorac) or plant growth retardant (ancymidol) in other circumstances. CBIs have been used to elucidate cellulose biosynthesis—unraveling the organization of cellulose synthase (CESA) complex including the assembly between CESA subunits—and the relation between cortical microtubules and cellulose deposition, as some CBIs interfere with the microtubule-guided deposition of cellulose microfibrils. In recent years, several Arabidopsis CBI-resistant mutants have been reported. Frequently, but not always, their mutations were related to genes directly involved in cellulose biosynthesis. In other cases, the effects of CBIs on plant growth have been used to associate the phenotype of a set of mutants to the impairment in their cellulose biosynthesis machinery. The habituation of cell cultures to grow in the presence of high concentrations of different CBIs has been proven to be a powerful tool for insight into the mechanisms underlying the plasticity of plant cell wall structure and composition. CBI-habituated cell cultures reflect the ability of cells to adapt their metabolism and modify their cell walls in order to cope with these new stressful conditions. New perspectives in CBI uses imply the selection of habituated cells having walls with a reduction in their cellulose content; the manipulation of levels and/or modification of matrix polysaccharides, rendering cell walls with new physicochemical properties; the study of the relationship between cellulose synthesis and other C-sink processes such as phenylpropanoid synthesis; or the elucidation of putative new targets implied in cellulose biosynthesis.