Rhamnogalacturonan II is a complex pectic polysaccharide that is an important component of the plant primary cell wall. A molecular genetic based approach is being adopted in Arabidopsis thaliana to identify the key roles of RGII during root development.
The plant primary cell wall is comprised of a complex set of polysaccharides including pectin, cellulose and hemicelluloses that are crucial for normal development. There are 3 major forms of pectin, homogalacturonan (HGA), rhamnogalacturonan I (RGI) and rhamnogalacturonan II (RGII). RGII is the least abundant pectin which has the same glacturonic acid backbone as HGA but is substituted with 4 side chains comprised of 12 different monosaccharides linked by 20 different glycosyl linkages. Some of these monosaccharides including D-apiose, 2-keto-3-deoxy-D-manno-octulosonic acid (Kdo) and 2-keto-3-deoxy-D-lyxo-heptulosaric acid (Dha) are rare in plants and possibly unique to RGII. Although RGII is a low abundance cell wall component, its structure is conserved in all vascular plants suggesting its function is important and that the structure is a critical feature for function. Despite the likely importance of RGII, little is known about its biosynthesis or function.
An ethanol inducible transactivation based system is being used to provide spatial and temporal control of the downregulation of genes involved in the synthesis of CMP-Kdo, an activated precursor that is used as a substrate during RGII biosynthesis. This will allow the role of RGII during specific developmental programmes such as root elongation, root hair formation and lateral root induction to be studied.
This work is funded by a BBSRC DTA studentship (2008-2012).