Arabidopsis and Brachypodium distachyon Transgenic Plants Expressing Aspergillus nidulans Acetylesterases Have Decreased Degree of Polysaccharide Acetylation and Increased Resistance to Pathogens      

Abstract

The plant cell wall has many significant structural and physiological roles, but the contributions of the various components to these roles remain unclear. Modification of cell wall properties can affect key agronomic traits such as disease resistance and plant growth. The plant cell wall is composed of diverse polysaccharides often decorated with methyl, acetyl, and feruloyl groups linked to the sugar subunits. In this study, we examined the effect of perturbing cell wall acetylation by making transgenic Arabidopsis (Arabidopsis thaliana) and Brachypodium (Brachypodium distachyon) plants expressing hemicellulose-and pectin-specific fungal acetylesterases. All transgenic plants carried highly expressed active Aspergillus nidulans acetylesterases localized to the apoplast and had significant reduction of cell wall acetylation compared with wild-type plants. Partial deacetylation of polysaccharides caused compensatory up-regulation of three known acetyltransferases and increased polysaccharide accessibility to glycosyl hydrolases. Transgenic plants showed increased resistance to the fungal pathogens Botrytis cinerea and Bipolaris sorokiniana but not to the bacterial pathogens Pseudomonas syringae and Xanthomonas oryzae. These results demonstrate a role, in both monocot and dicot plants, of hemicellulose and pectin acetylation in plant defense against fungal pathogens.The cell wall is one of the most important compartments of the plant cell. This external cell skeleton plays an important role in cell and tissue shape determination. Besides its structural role, this extracellular complex is involved in the control of important functions such as cell-cell interactions, whole-plant growth, development, and interaction with the environment. The plant cell wall is mainly composed of highly dynamic heteropolysaccharides assembled in macromolecular Besides the diversity of monosaccharide composition, cell wall polysaccharides are also modified with methyl, acetyl, and feruloyl groups, which are mainly O-linked to sugars. These functional groups are believed to protect polysaccharides from the action of specific glycosyl hydrolases and to cross link cell wall constituents controlling cell extensibility (Perrone et al., 2002;Gou et al., 2012). For example, methylesterification/

Brachypodium as an emerging model for cereal–pathogen interactions

“…Pogorelko et al (2013) found that transgenic brachypodium lines (ecotype Bd21) expressing a xylan-specific acetylesterase from Aspergillus nidulans (designated AnAXE) showed significantly decreased cell-wall acetyl content, indicating that cellwall xylans were deacetylated in the transgenic lines. Cell-wall morphology and thickness was not altered in the AnAXEexpressing transgenics compared with the wild-type Bd21, as assessed by microscopic examination.…”

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

“…O-Acetylation of xylan was recently demonstrated to occur primarily on alternating xylosyl residues, allowing for the adsorption of xylan onto cellulose microfibrils, with the acetyl groups facing outward and increasing the hydrophobicity of the microfibrils (Busse-Wicher et al, 2014). Interestingly, expression of a fungal xylan acetylesterase in Arabidopsis was reported to result in a 50% decrease in stem O-acetyl content, a similar reduction to that in the tbl29/esk1 mutant, without resulting in a growth phenotype for the plants (Pogorelko et al, 2013;Xiong et al, 2013). This suggests that the timing or distribution of xylan O-acetylation depletion has functional implications for the wall.…”

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

“…A CE7 AcXE gene has recently been modified by site-directed mutagenesis to create a perhydrolytic enzyme with improved activity for the production of perhydrolytic acids applicable in laundry care and disinfectant formulations [163]. AcXEs have also been employed in deacetylation of other acetylated polysaccharides [40] as well as in the post-synthetic (in planta) deacetylation of xylan to enhance lignocellulose saccharification [7,8,164,165]. In synthetic carbohydrate chemistry, AcXEs can potentially be harnessed in catalyzing regioselective transacetylation reactions [23,24,166].…”