RGII

RGII, short for rhamnogalacturonan II, is a highly conserved and structurally complex pectic polysaccharide that forms part of the plant cell wall. It is one of the major domains of pectin, alongside rhamnogalacturonan I and homogalacturonan, and is characterized by a relatively small, branched molecule with a backbone of galacturonic acid residues decorated by diverse side chains.

The precise composition of RGII varies among plant species, but its side chains typically include a range of rare and unusual sugars. This structural complexity is a focus of plant cell wall biology, as RGII contributes to the integrity and properties of the wall, including porosity and mechanical strength. RGII is synthesized in the Golgi apparatus and secreted to the cell wall, where it becomes covalently incorporated into the pectin matrix.

A notable feature of RGII is its ability to form borate cross-links between RGII molecules, producing borate diesters that help stabilize the cell wall. This boron-dependent cross-linking influences wall architecture and has been implicated in processes such as cell expansion and plant growth, particularly under varying boron availability.

RGII is widespread in land plants, appearing in many tissues and developmental stages. In research and industry, RGII-rich pectin fractions are of interest for understanding cell wall mechanics, plant physiology, and the textural properties of plant-derived foods. See also pectin, RG-I, homogalacturonan, and boron in plants.