Loss-of-Function Mutation of REDUCED WALL ACETYLATION2 in Arabidopsis Leads to Reduced Cell Wall Acetylation and Increased Resistance to Botrytis cinerea      

Abstract

Nearly all polysaccharides in plant cell walls are O-acetylated, including the various pectic polysaccharides and the hemicelluloses xylan, mannan, and xyloglucan. However, the enzymes involved in the polysaccharide acetylation have not been identified. While the role of polysaccharide acetylation in vivo is unclear, it is known to reduce biofuel yield from lignocellulosic biomass by the inhibition of microorganisms used for fermentation. We have analyzed four Arabidopsis (Arabidopsis thaliana) homologs of the protein Cas1p known to be involved in polysaccharide O-acetylation in Cryptococcus neoformans. Loss-of-function mutants in one of the genes, designated REDUCED WALL ACETYLATION2 (RWA2), had decreased levels of acetylated cell wall polymers. Cell wall material isolated from mutant leaves and treated with alkali released about 20% lower amounts of acetic acid when compared with the wild type. The same level of acetate deficiency was found in several pectic polymers and in xyloglucan. Thus, the rwa2 mutations affect different polymers to the same extent. There were no obvious morphological or growth differences observed between the wild type and rwa2 mutants. However, both alleles of rwa2 displayed increased tolerance toward the necrotrophic fungal pathogen Botrytis cinerea.

The Role of the Plant-Specific ALTERED XYLOGLUCAN9 Protein in Arabidopsis Cell Wall PolysaccharideO-Acetylation

“…the Golgi lumen, implying that AXY9 acts downstream from the RWA proteins, which have been proposed to transport an activated form of acetate into the Golgi (Manabe et al, 2011). Acetyl-CoA has been shown to be an upstream donor of acetyl groups for the acetylation of pectin; however, it has not been shown whether acetyl-CoA itself is transported into the Golgi or if there is an alternative intermediate carrier molecule (Pauly and Scheller, 2000).…”

“…For this reason, and because the RWA proteins are integral membrane proteins with 10 predicted transmembrane domains, it has been hypothesized that they may act as transporters for an activated form of acetate into the Golgi apparatus (Manabe et al, 2011). It has been demonstrated that acetyl-CoA is involved in the pathway of pectin acetylation (Pauly and Scheller, 2000); however, it is not clear if acetyl-CoA is transported into the Golgi or there is an alternative donor substrate that acts as a carrier.…”

“…While the TBL gene products seem to affect single wall polysaccharides, Arabidopsis mutants defective for one or more of the four RWA genes have decreased acetylation of multiple polysaccharides and growth phenotypes ranging from mild to severe (Lee et al, 2011;Manabe et al, 2011Manabe et al, , 2013. For this reason, and because the RWA proteins are integral membrane proteins with 10 predicted transmembrane domains, it has been hypothesized that they may act as transporters for an activated form of acetate into the Golgi apparatus (Manabe et al, 2011).…”

Two Trichome Birefringence-Like Proteins Mediate Xylan Acetylation, Which Is Essential for Leaf Blight Resistance in Rice

“…RWAs consist of 10 transmembrane helices homologous to the CnCas1p from Cryptococcus (Manabe et al, 2011). Arabidopsis (Arabidopsis thaliana) possesses four RWA homologs in its genome, and mutation of RWA2 results in an overall reduction of acetylation on several polymers (Manabe et al, 2011). The quadruple mutant of all four RWA genes exhibited similar but more severe defects (Lee et al, 2011), indicating that RWAs might function as transporters by supplying acetyl-donor(s) for polysaccharide O-acetylation into the Golgi apparatus (Gille and Pauly, 2012).…”

“…RWAs consist of 10 transmembrane helices homologous to the CnCas1p from Cryptococcus (Manabe et al, 2011). Arabidopsis (Arabidopsis thaliana) possesses four RWA homologs in its genome, and mutation of RWA2 results in an overall reduction of acetylation on several polymers (Manabe et al, 2011).…”