PAE

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Introductions

Pectin consists of complex polysaccharides that are present in the primary cell walls of plants and are abundant in the green parts of terrestrial plants. Pectin is the main component of the intermediate lamellae, which bind the cells. Pectin is deposited into the cell wall through vesicles produced in the Golgi apparatus by cytosolic action. The amount, structure and chemical composition of pectin vary between plants, within plants over time and in different parts of the plant. Pectin is an important cell wall polysaccharide that allows primary cell wall extension and plant growth. During fruit ripening, pectin is broken down by pectinase and pectin esterase, a process in which the fruit becomes softer as the middle lamellae break down and cells separate from each other. A similar process of cell separation caused by pectin breakdown occurs in the abscission zone of petioles of deciduous plants.

Pectin acetylesterases (PAEs)

Pectin is a plant cell wall polysaccharide that can be acetylated on C2 and/or C3 of galacturonic acid residues. The acetylation degree of pectin can be regulated by pectin acetylesterase. PAE is a kind of pectinesterase. Pectin esterase includes pectin methylesterase and pectin acetylesterase. Pectin methylesterase (PME) acts on the C-6 carboxyl group of galacturonic acid residues of polygalacturonic acid, removes methyl esters, and catalyzes the conversion of pectin ester acid to pectin acid. Pectin acetylesterase acts on the C-2 or C-3 carboxyl group of galacturonic acid to acetylate it.

Research Progress

The plant pectin acetylesterases (PAEs) belong to the carbohydrate esterase family 13, and their enzymatic activity for pectin deacetylation was first characterized in vitro. These proteins can hydrolyze the acetyl ester bonds of pectins, but the substrate specificity have not been demonstrated. Overexpressing PAE in tobacco showed decreased acetylation level of pectin and affected the growth of pollen tubes and the germination of pollen grains. Besides playing a key role in plant growth, development, and reproduction, PAEs are involved in the plant-microbe interactions. Overexpression of fungal PAE in Arabidopsis thaliana leads to resistance to specific fungal pathogens and the up-regulation of some genes involved in pectin O-acetylation, suggesting that pathogen PAE may be perceived by host plant and therefore induce host resistance. The paeY mutant of Erwinia chrysanthemi was less capable of host invasion compared to the wild-type strain, indicating the importance of PAE in the soft-rot disease progress. PAEs from pathogenic fungi consume host pectin as a carbon source. Distinct growth profiles of the twelve fungi on pectins and pectin structural elements may (at least partially) be due to differences in carbohydrate-active enzymes contents, including PAEs, in these fungal genomes.

Function

It has been shown that pectin methylesterase (PME) regulates pectin demethylation, which increases the number of free radicals in pectin and thus the ability of the cell wall to adsorb and bind more heavy metal ions.PAE may be involved in the enrichment and detoxification of heavy metals by the plant cell wall through the regulation of pectin acetylation as well as PME. PAE may be involved in the enrichment and detoxification of heavy metals by the plant cell wall through the regulation of pectin acetylation.